4 Common Causes of Inadequate Drainage on Low-Slope Roofs

Photo 1. Roof decks with poor slope, drains that are up slope and deck defection can result in excessive ponding. Images: Hutchinson Design Group Ltd.

The stone church in rural Portugal was constructed some 700 years ago. The roofs of the transepts are large stone slabs: 5 feet wide, 10 feet to 12 feet long, and 8 inches thick. How they even made it into place is amazing, but to those like us who think in terms of water, what is even more amazing is the carved-out drainage channels. Moving water off the roof was important to builders 700 years ago in Europe, just as it was to the builders of Machu Picchu and Angkor Wat. Along with many indigenous building methods, the movement of water off roofs and away from buildings is becoming a lost design element.

It is not uncommon to walk upon recently installed roofs and see ponding at gutters, roof drains and across the roof. There are many reasons for this degradation of roof system design, including ignorance. A lack of knowledge by designers, a “roofer or builder will figure it out” mentality, and poor installation procedures can all be to blame.

Ponding water provides visual evidence to the owner that something isn’t quite right, and in some instances, it can result in roof structure collapse. If breaches in the roof membrane exist, standing water can result in excess moisture intrusion. (See Photo 1.) Additionally, water on the roof promotes algae growth that can attack some materials. It also allows for ice to form in winter, creating life safety issues as well as external forces affecting the roof cover.

So, what can you do?

In this article we’ll look at four key conditions on the roof that I see as the most erroneously conceived and installed:

  1. The roof system’s transition to the gutters
  2. Two-way structurally sloped roof decks with roof drains above the low point
  3. Four-way structurally sloped roof decks with drains above the low point
  4. Roof drains on level roof decks with tapered insulation

Accumulated Debris at Gutters

As perhaps you know and will see within this article, there are many things that irk me; one is walking on a new roof and seeing a 3- to 4-foot wide swath of black accumulated dirt and airborne components in front of the gutter. This situation

Photo 2. Owners do not like seeing ponding in front of their gutters, especially when it’s egregious. Proper design and installation would have prevented this problem. Images: Hutchinson Design Group Ltd.

results from restricted water drainage, and it is especially noticeable on reflective roof covers. (See Photo 2.) This restriction of water drainage can be due to several possible factors, including roof edge wood blocking that is too high, insulation that is too low, and the accumulation of roofing material above the slope plane. The roof deck itself can also be set too low.

When designing roof edge gutters, there are key design elements to consider:

  • Wood blocking:In addition to being of appropriate width and anchorage, wood blocking should be sloped to drain, even with sloped roof decks with an elevation 1/4 inch to 3/8 inch below the anticipated roof insulation height. The greatest error I see with most architects is that they do not draw the detail to scale. Insulation is not of the correct thickness, the wood is too big or too small, or it is depicted as one giant block floating atop the wall with no mention of anchorage.
  • Insulation:Please read the ASTM standard for polyisocyanurate and you will learn that the ISO has an allowable dimensional change. Thus, if you specified two layers of 2.25-inch ISO to match three layers of two-by wood blocking, you might be in for a surprise. You might get to the field and see that your two layers of insulation are 3/8 of an inch below the top of the wood, and the manufacturer whom you’ve complained to will pull out the ASTM standard and say, “We are within tolerances.”
  • Material layering:When the roof membrane is taken over the wood (yes you should do this) and sealed to the wall substrate, and the gutter is set in mastic and then stripped in, the accumulated material thickness can exceed 3/8 of an inch. Not much, you say, but on a roof with a 1/4-inch-per-linear-foot slope, that can result in 18 inches of ponding right in front of the gutter. Ouch.

Design recommendations for achieving complete drainage at the roof edge with gutter include:

  • Communicate with the structural engineer.Coordinate with the structural engineer to determine the elevation of the wall (less wood blocking) with the structure and roof deck. If perimeter steel angles attached to the wall rise above the roof deck, discuss with the structural engineer turning the angle downward or changing the angle to one with a vertical leg that doesn’t rise above the roof deck. Angles that rise above the roof deck create a void when

    Photo 3. Even when using tapered insulation and on four-way sloped roof decks, it is advantageous to accentuate the slope into the drain. Here a 1/2-inch-per-foot tapered insulation sump matches up to the tapered insulation with the help if a 1/2-inch tapered edge strip. Images: Hutchinson Design Group Ltd.

    the first layer of insulation is set that is most often not sealed, resulting in a thermal short and a place where dew points can be reached and condensation can occur. If reinforcing paper facers are on the insulation, mold growth can result.

  • Properly detail the wood blocking. I prefer and recommend the use of two layers of wood blocking. First off, do not use treated wood; use untreated Douglas fir. The wood should be at a minimum 8 inches wide (preferably wider) so that the gutter flange can have nail locations back far enough to allow for 3-inch minimum overlap on the stripping-in ply.

Often it is best if the top of the wall is sealed prior to the installation of the wood to prevent air/moisture transport to the wood, and on precast, to prevent the migration of “damp” into the wood. The first layer of wood should be anchored to the structure (wall or framing). While not always required, I prefer to set anchors at 2 feet on center, staggered. This spacing prevents the warping of the wood. The second layer of wood should match the first in width. I suggest that this second layer of blocking be sloped, and placing a continuous shim along the roof side on the first layer will provide the proper slope. The shim width and thickness are dependent on the wood size, but for two-by-ten wood blocking, a shim of 1/2 inch by 1.5 inches will work well. The second layer of wood blocking should be set with joints offset from the lower layer and then screw fastened at 12 inches on center, staggered. Joints on both layers should be scarfed at 45degrees and screwed tight. On your detail, the height of the wood blocking at the interior side above the roof deck should be dimensioned. This will allow contractors to identify height concerns well before the installation of the insulation so adjustments can be made if necessary. I suggest that this distance be 1/4 inch to 3/8 inch below the top surface of the roof insulation or cover board atop the insulation. (See Figure 1.)

  • Make sure the insulation is higher than the wood blocking.We will not discuss insulation types, substrate boards (vapor barriers) and cover boards in this article; please see earlier articles on the topic. In designing the roof edge and discussing/coordinating with the structural engineer, the goal is to have the insulation system: substrate board, vapor retarder, cover board. The thickness should be 3/8 of an inch greater than the interior top corner of the wood blocking. One key item to remember is that spray-and-bead polyurethane adhesive adds 3/8 of an inch thickness per layer. Designing the insulation to be higher than the wood blocking is important, as it compensates for that allowable dimensional change mentioned above, as well as the thickness created by the layers of gutter flange and roofing. The goal is to create a condition in which water will flow over and into the gutter.

Two-Way Structurally Sloped Roof Decks

Often long, narrow roof areas are designed with a two-way structurally sloped roof deck designed to move water from the outer roof edge to a central point. Prudent designers would like the roof drains to be located at the low point of the structurally sloped roof deck. Typically, though, there is a steel beam at the low point, which prevents the installation of the roof drain at the low point. Consequently, the roof drains must be located on the plumbing drawings up slope from the low point. I have tried for years to explain to plumbing engineers that water doesn’t typically flow uphill, but to no avail, so we as the roof system designer have to fix it. How? By moving the low point.

How is this design goal accomplished?

Let’s start with our roof system design for the following example: a new construction project in Chicago (R-30 minimum) with a steel roof deck, two-way structural slope and the low point over a steel beam. The plans call for the drains to be installed 2 feet up slope, and thus they will be more than 1/2 inch above the low point.

The goal will be to move the structural low point to the drain line. With a structural slope, to meet the thermal value we are looking at two layers of 2.6-inch insulation. Run the first layer of 2.6-inch insulation throughout the roof. Then the fun begins: Draw a line down the center of the roof drains. From this centerline, come out 4 feet on each side with a 1/2-inch-per-foot tapered edge board (Q panel, for those who know). The next layer of 2.6-inch insulation abuts the taper. The tapered insulation at the drain line effectively moves the low point to the drains. (See Figure 2.)

Now that the water is being moved to a new low point, it then needs to be moved to the drains. This is accomplished by saddles. (See Figure 3.) Sounds simple enough, but 95 percent of the saddles I see are incorrect, and water ponds on them, over them and along them. This situation leaves, once again, a bad taste in the mouth of the owner, general contractor, construction manager, and architect — even though it’s the designer’s problem. So, I will now, for the first time, reveal my secret developed years ago: The taper of the saddles mustbe twicethe roof deck slope. If the deck slopes 1/4 inch per foot, the saddles must slope at 1/2 inch per foot. If the deck slopes at 3/8 inch per foot, as it often does, the saddle needs to be at 3/4 inch per foot. And, architects and designers, the slope of the saddle is to the valley line, not the drain. The width of the saddle is the key and determining the width of the saddle is my secret.

It’s a simple formula:

(Distance Between Drain)x 33% = X

2

Increase X to the next number divisible by 4

Example: If the drains are 60 feet apart, divide 60 by 2 to get 30 feet; multiply 30 feet by 33% = 9.9 feet. Increase 9.9 to the next number divisible by 4 to get the answer: 12 feet.

Thus, the saddles at the mid-point apex should extend out three full tapered insulation boards. It’s best if you dimension this width on the detail.

On large buildings, the saddle width and thickness can be quite high, so be sure to double-check the insulation height with the height of the roof edge. I could tell you about a roof where the insulation rose several inches above the perimeter height because someone didn’t draw the detail to scale, but that is a story for another time.

Roof Drains in Four-Way Slope Roof Decks

Structurally sloped roof decks can be beneficial in that they can create positive drainage flow. But with four-way structurally sloped roof decks, the drain is not necessarily at the low point of the roof. How far off the low point is dependent on the plumbing contractor. I have seen drains installed several feet upslope. The plumbing drawings should have a note to the fact that the roof drain sump pan should be installed as close to the low point as possible.

Even when the drain is installed very close to the low point, it is still high and will result in water ponding in front of the drain. Thus, the low point needs to be artificially moved to the drain.

This is accomplished with a drain sump. Best practices suggest that the roof insulation be installed in two layers. This will allow for the installation of the sump.

Using Chicago as an example, which calls for R-30 or 5.2-inches of insulation, the first layer of insulation 2.6 inches thick is installed across the roof deck, to the roof drain. It should be cut to the roof drain extension ring. Fill the void between the roof drain and the insulation with spray foam; trim to the insulation. Next the tapered insulation sump is installed. To match the next layer of insulation, we use 1/2-inch-per-foot tapered insulation. It starts at 1/2 inch and, with a 4-foot panel, rises to a thickness of 2.5 inches. Placed around the drain, the sump created is 8 feet by 8 feet. The next layer of insulation is 2.5 inches and abuts the backside of the tapered insulation.

The 1/2-inch-per-foot slope is used as it doubles the slope of the structurally sloped roof deck, which in this case has a slope of 1/4 inch per foot.

Level Roof Decks With Tapered Insulation

Whether re-roofing or new construction, getting the drainage correct on level roof decks is still a challenge for most designers. Perhaps they don’t realize decks are not level; they have camber, they deflect, they undulate, and the drains are often near columns so the drain pipe can run along it. When the drain is near a column where no deflection takes place, it can often be high.

I like to first ensure the proper drain assembly has been selected and designed by the plumbing engineer: the roof drain, reversible collar, threaded extension ring, clamping ring, cast iron dome. (For more detail, see “Roof Drain Installation Tips” on page XX of this issue.) The sump pan should be selected and designed by the plumbing engineer and provided by the roof drain manufacturer — not by the metal deck supplier. (That the industry cannot get this correct is one on my pet peeves.) Do not raise drains off the deck with threaded rods. (See my article “Concise Details and Coordination Between Trades Will Lead to a Quality Long-Term Solution for Roof Drains,” RoofingMay/June 2016). If designing in a vapor retarder, it needs to extend to the roof drain flange and be clamped by the reversible collar. The first layer of insulation should be cut to fit and extend under and to the extension ring. Any voids should be sealed with spray foam.

To compensate for all the potential deck irregularities, I like to accentuate the slope into the roof drain by increasing the taper. More often than not, this means designing a 1/2-inch-per-foot slope sump into the drain. With a 4-foot board, this results in an 8-foot-by-8-foot sump. (See Figure 4 and Photo 3.) After detailing this sump, the main roof four-way tapered insulation can be designed and the heights at the perimeter calculated and noted on the plans. Just a reminder that the code-required thermal value needs to be attained four feet from the drain. So, for Chicago we detail to achieve R-30 at the backside of the tapered sump.

Final Thoughts

A new roof installation that results in ponding water at the drainage point is an unfortunate occurrence. Owners can be upset: “What is that?” “I didn’t pay to have water retained at the drains!” “Who is coming up and cleaning all this stuff off my roof?” Ponding water can be a standard of care issue for designers and result in damages. Learning to properly design rooftop drainage is not difficult, but it requires some thinking and some rooftop experience. Getting up on the roof during installations will help you visualize the needs to achieve proper drainage.

Making sure the roof system drains properly requires discussions with the structural engineers for new construction. I also find it helpful to have the plumbing contractor at pre-con meetings to review the interrelationship of the roofing and drains.

Getting water off the roof as quickly as possible has been a key priority for centuries — no matter the roof cover material. If the builders using stone can achieve complete and full drainage, then I challenge you to achieve it with the materials we use today.

Are You Meeting Thermal Insulation Code Requirements?

Photo 1. Conditions such as this, in which the fastener plates melt the snow, visually demonstrate the heat loss that is a known entity to roof installers and knowledgeable roofing professionals.

You may have overheard conversations such as this:

New Building Owner: “You promised energy conservation and savings.”

Mechanical Engineer: “We sized the mechanical unit based on the code required effective thermal value.”

New Building Owner: “But why are my cost 30 percent above your estimates and I am needing to run my units constantly and they still barely maintain a comfortable environment?”

Mechanical Engineer: “We have checked all the set points and systems and they are all working, albeit with a bit of laboring. We don’t know why there is not enough heat.”

New Building Owner: “Well, someone is going to have to pay for this!”

Scenarios and liability questions like this are being repeated across the northern North American continent, and to mechanical engineers, architects and owners, the cause is a mystery. Perhaps they should have talked to seasoned roofing professionals and consultants. They could’ve told them that many mechanically attached roofs, incorrectly promoted and sold as energy-saving systems, were actually energy pigs. One only needed to walk a mechanically attached roof with a few inches of snow on it to see the heat loss occurring. It doesn’t take scientific studies and long-winded scenarios to prove this — just get up on the roof and see it. (See Photo 1.)

Photo 2. When a light dusting of snow blew off this 2 million-square-foot facility in central Illinois, every single mechanical fastener and insulation joint could be identified by the ice visible at their locations. This roof needed to be replaced due to condensation issues several years after installation at a cost of more than $10 million.

I spoke on this topic back in 2007 at the RCI Cool Roofing Symposium. I always like being a soothsayer, and several recent studies are demonstrating and attempting to quantify this energy loss that most roofers could tell you was there.

For years the NRCA suggested a loss of thermal value of 7 percent to 15 percent through the joints in a single-layer insulation application and through mechanical fasteners used to secure the insulation. (The NRCA has since removed this figure and suggests that professionals be consulted to determine thermal heat loss.) The NRCA recommended a cover board to reduce this effect. This was at a time when roof covers were predominantly BUR, modified bitumen or adhered single plies. The upsurge in mechanically attached single-ply membranes, brought on by low-cost installation and the promise of energy savings, changed the game. No one was asking, if there could be a loss of 7-15 percent when mechanically attaching insulation, what could the effective R-value loss be when we install thousands of fasteners and plates 12 inches on center (or less) down a membrane lap seam? Gee, haven’t we seen that before?

Code Requirements

The code and standard bodies — ICC, IECC, ASHRAE — have been repeatedly raising required thermal insulation values over the past decade in an attempt to conserve energy; that is their intent. They listened to astute designers and

Photo 3.This is close-up of the roof shown in Photo 2. Heat loss through the screws and fastener plates and through joints in the single layer of insulation melted the snow. The water froze when the temperatures dropped and the ice was revealed when a light wind pillowed the membrane and the remaining snow blew away.

prescribed two layers of insulation, and then again to determine the minimum R-value and not allow averages. The intent is clear. The required R-value per ASHRAE zone is to be achieved.

Their goals were laudable, but not all roof systems achieved the in-place R-values required. So, this article is in part an attempt to educate code officials and explain the need for a change.

Words can explain the phenomenon of thermal loss, but photos are worth a thousand words, and since my editor has told me that I cannot have a 4,000-word article, I leave it to the photos to do the talking. (See Photos 2, 3 and 4.)

Scientific Studies

In their Buildings 2016 article titled “Three-Dimensional Heat Transfer Analysis of Metal Fasteners in Roofing Systems,” Singh, Gulati, Srinivasan and Bhandari (Singh) studied the effect of heat transfer through thermal bridging (mechanical fasteners) in various roof assembly scenarios.

Their study exposes a shortfall in many standards that have as their goal a reduction in energy loss through building envelope systems through prescriptive approaches. For roofing assemblies, standards prescribe a minimum R-value, but they do not take into consideration the heat loss that happens though metal fasteners. There are no guidelines or recommendations in regards to thermal loss, including the loss of heat through roof system fasteners. It’s actually ignored.

Figure A: The effect of mechanical fasteners below the roof cover in mechanically attached roofs is not negligible as considered by general standards. As can be seen here for systems 1A and 1 B, in which mechanical fasteners are used in the lap seams of the roof cover (systems 3A and 3B have the fasteners below a layer of insulation), the actual thermal value loss caused by mechanical fasteners can be as high as 48 percent, as seen in system 1A with a high density of mechanical fasteners. As the mechanical fastener density decreases (1B), the heat loss also decreases. Thus, a correlation appears to exist in which heat loss due to thermal bridging is proportional to the fastener density.

The results of the Singh study, as seen in the graph (Figure A), show that the effects of thermal shorts, e.g., mechanical fasteners used to secure the roof cover, is not negligible. In fact, thermal shorts can result in a loss of 48 percent of the effective value. Read that again! The thermal value of the roof insulation layer on which the mechanical engineer has in part sized the mechanical equipment — and which the owner is counting on for significant energy savings — could be about half of what was assumed. Add in gaps and voids, and the loss in the effective R-value could top 50 percent. What that means is that to achieve the code required R-30, say in Chicago, mechanically fastened roof systems need to have R-45 in the design to meet the effective code required R-value. This last sentence is for the code bodies — are you listening?

The value of this study cannot be underestimated, as thousands of buildings have been constructed since its publication that would not meet an effective R-value check in a commissioning study.

Changing the Code

The energy inefficiency of mechanically attached roof systems in ASHRAE zones 4 and above has been known to roofing crews for decades. Now, with the requisite scientific studies completed, the codes need to be revised to reflect the inherent thermal loss through mechanical fasteners. Additionally, studies from Oak Ridge National Laboratory highlight the energy increase required with inherent air changes below the membrane, confirming the need for air/vapor barriers on the deck on mechanically attached roof assemblies. (See “The Energy Penalty Associated with the Use of Mechanically Attached Roofing Systems,” by Pallin, Kehrer and Desjarlais.)

Photo 4: Heat loss also occurs through adhered roofs when the insulation is mechanically attached.

As a starting point for code groups and officials, I suggest the following code revisions:

  1. State that if a mechanically attached roof cover is being used that the prescribed thermal R-value shall be increased by 50 percent.
  2. State that if a mechanically attached roof cover is being used that an air barrier below the insulation must be used and that it shall be fully adhered to penetrations and roof perimeters.

Closing Thoughts

The goal of energy conservation is a laudable one. The American Institute of Architects’ goal of zero-energy building by 2030 will never be met until real-world empirical information can be presented at code hearings. (For those of you who do not attend code hearings or know the process, information is usually disseminated in two-minute sound bites without documentation.) This lack of information sharing is a travesty and has resulted in numerous code changes that have been detrimental to the goal of energy savings. Time has come for a new way of thinking.

Single-Ply Roofing Best Practices: Doing Everything Right the First Time.

Figure 1: Designing resilient roof systems is the best of practices. When developing details, we find it very helpful to draft out the roof system (for each different system), noting materials and installation methods. Photos: Hutchinson Design Group

Single-ply membranes have risen from being the “new guy” in the market in the early ’80s to become the roof cover of choice for most architects, consultants and contractors. Material issues have for the most part been resolved, and like no other time in recent history, the industry is realizing a period of relative calm in that regard. Whether EPDM, TPO or PVC, the ease of installation, the cleanliness of the installation (versus the use of hot or cold bitumen), the speed at which they can be installed, and the material costs all blend to make these materials a viable option for watertight roofing covers. But with this market share comes issues and concerns, some of which are hurting owners, giving forensic consultants such as myself too much business, enriching attorneys, and costing contractors and, at times, designers dearly.

Following are some of my thoughts on various issues that, in my opinion, are adversely affecting single-ply membrane roof systems. Paying attention to these issues will bring about best practices in single-ply applications.

Specifying the Roof by Warranty

OMG, can architects do any less? Don’t get me started. The proliferation of “canned” Master Specs which call for a generic 10-year or 20-year warranty and then state to install the product per manufacturer’s guidelines is disheartening. Do

Figure 2: Coordinating with the mechanical engineer in the detailing of the pipe penetrations is critical. Here you can see all the components of the curb, penetrations, roofing and waterproofing are noted. We recommend that the same detail be on the mechanical sheets so that at least an 18-inch curb is known to all. Photos: Hutchinson Design Group

designers realize that manufacturers’ specifications are a market-driven minimum? When architects leave out key details, they are simply relying on the roofing contractor to do what is right. This deserves another OMG. The minimum requirements for a warranty can be very low, and the exclusions on a warranty quite extensive. Additionally, a design that calls for products to be installed based on achieving a warranty may result in a roof system that does not meet the code. Owners are often oblivious to the warranty requirements, and all too often fail to ensure the standard of care until the service life is shortened or there is storm damage — sometimes damage the roof should have withstood if it were properly designed and detailed.

If one is not knowledgeable about roof system design, detailing and specification, then a qualified roof consultant with proven experience in single-ply membranes should be retained. Roof systems and their integration into the impinging building elements need to be designed, detailed and specified appropriately for the building’s intended use and roof function. By way of example, we at Hutchinson Design Group typically design roof systems for a 40- to 50-year service life (see Figure 1); the warranty at that point is nice, but almost immaterial. Typical specifications, which are project specific, cover all the system components and their installation. They are typically 30 pages long and call out robust and enhanced material installations.

More Than the Code

I recently had a conversation with a senior member of a very large and prominent architectural firm in the Chicago area and inquired about how they go about designing the roof systems. The first thing he said was, “We do what is required by code.”

Photo 1: The roof drain sump pans shown here were provided and installed by the plumbing contractor, not the steel deck installer. Having the roof drain level with the top of the roof deck allows for a proper integration of the roof drain and roof system.

What I heard was, “We give our clients the absolute poorest roof the code allows.” An OMG is allowed here again. Does it really need to be said again that the code is a minimum standard — as some would say, the worst you are allowed to design a building by law? Maybe you didn’t realize it, but you are allowed to design above the code. I know this will shock a few of you, but yes, it’s true. Add that extra anchor to prevent wood blocking from cupping. Add extra insulation screw fasteners to improve wind uplift resistance; if too few are used, you may meet the code, but your insulation will be susceptible to cupping. Add that extra bead of polyurethane adhesive. (If I specify 4 inches on center, then perhaps by mid-day, on a hot and humid day, I might get 6 inches on center — as opposed to specifying 6 inches or 8 inches on center, and getting 12 inches on center in spots.) Plan for construction tolerances such as an uneven decks and poorly constructed walls. Allow for foot traffic by other trades. These types of enhancements come from empirical experiences — otherwise known as getting your butt in the ringer. Architects need more time on the roof to observe what goes on.

It’s About Doing What is Right

Doing it right the first time isn’t all that difficult, and it’s certainly less stressful than dealing with the aftermath of doing so little. The cost of replacing the roof in the future could easily be more than double the original cost. Twenty years ago, I

Figure 3: Coordinating with the plumbing engineer, like coordinating with the mechanical engineer, is a requirement of best practices. In this drain detail, we can see the sump pan is called out correctly, and the roof drain, integration of the vapor barrier, extension ring, etc., are clearly defined. Photos: Hutchinson Design Group

chaired an international committee on sustainable low-slope roofing. At that time, the understanding of sustainability was nil, and I believe the committee’s Tenets of Sustainability, translated into 12 languages, helped set the stage for getting designers to understand that the essence of sustainability is long-term service life. That mantra seems to have been lost as a new generation of architects is at the helm. This is unfortunate, as it comes at a time when clients no longer ask for sustainable buildings. Why? Because they are now expected. The recent rash of violent and destructive storms — hurricanes, hail, intense rain, high winds and even wildfires — have resulted in calls for improvement. That improvement is called resiliency. If you have not heard of it, you are already behind. Where sustainability calls for a building to minimize the impact of the building (roof) on the environment, resiliency requires a building (roof) to minimize the impact of the environment on the building. This concept of resiliency requires designing a roof system to weather intense storms and to be easily repaired when damaged. (Think of Puerto Rico and consider how you would repair a roof with no power, limited access to materials, and manpower that might not be able to get to your site.)

Achieving resiliency requires the roof system designer to:

  1. Actually understand that roofs are systems and only as good as their weakest link. Think metal stud parapet and horizontal base anchor attachment; only forensic consultants and attorneys like to see screws into modified gypsum boards.
  2. Eliminate your old, out-of-date, incorrect details. Lead vent flashing and roof cement cannot be used with single-ply membrane.
  3. Design the roof system integration into associated barrier systems, such as where the roofing membrane (air/vapor retarder) meets the wall air barrier. You should be able to take a pencil and draw a line over the wall air barrier, up the wall and onto the roof without lifting it off the sheet. If you cannot, you need to redesign. Once you can, you need to consider constructability and who may get there first — the roofer or air barrier contractor. Then think material compatibility. Water-based air barrier systems don’t react well when hit with a solvent-based primer or adhesive.

    Photo 2: This roof drain is properly installed along with 6 inches of insulation and a cover board. The drain extension ring is 1/2 inch below the top of the cover board so that the water falls into the drain and is not held back by the clamping ring, resulting in ponding around the roof drain.

    Perhaps the roofing needs to be in place first, and then the air barrier brought over the top of the roofing material. This might require a stainless-steel transition piece for incompatible materials. Maybe this requires a self-adhering membrane over the top of the roof edge prior to the roofing work, as some membranes are rather rigid and do not bend well over 90-degree angles. You as the designer need to design this connectivity and detail it large and bold for all to see.

  4. Design the roof system’s integration into the impinging building elements, including:
  • Roof curbs for exhaust fans: Make sure they are insulated, of great enough height, and are not installed on wood blocking.
  • Rooftop unit (RTU) curbs: The height must allow for future re-roofing. Coordinate with the mechanical engineer regarding constructability – determine when the curb should be set and when the HVAC unit will be installed. Roof details should be on both the architectural and mechanical drawings and show the same curb, drawn to scale. Be sure the curb is insulated to the roof’s required R-value. Avoid using curb rails to support mechanical equipment. The flashing on the interior side of the rails may be inaccessible once the equipment is placed. Use a large curb where all four sides will remain accessible.
  • Piping penetrations: Detail mechanical piping penetrations through the roof and support of same, where insulation and waterproofed pipe curbs are needed (see Figure 2). If you are thinking pourable sealer pocket, stop reading and go sign up for RCI’s Basics of Roof Consulting course.
  • Roof curbs, RTU, pipe curbs and rails: Coordinate their location and show them on the roof plan to be assured that they are not inhibiting drainage.
  • Roof drains: Coordination with the plumbing engineer is essential. Sump pans should be installed by the plumbing contractor, not the steel deck installer (see Photo 1), and the location should be confirmed with the structural engineer. Be sure drains are located in the low point if the roof deck is structurally sloped — and if not, know how to design tapered insulation systems to move water up that slope. Do not hold drains off the deck to meet insulation thickness; use threaded extensions. Be sure any air/vapor barrier is integrated into the curb and that the insulation is sealed to the curb. I like to hold the drain flange a half-inch down below the insulation surface so that the clamping ring does not restrain water on the surface. Owners do not like to see a 3-foot black ring at the drain, where ponding water accumulates debris (see Figure 3 and Photo 2).
  1. Understand the roof’s intended use once the building is completed. Will the roof’s surface be used for anything besides weather protection? What about snow removal? Will there be excessive foot traffic? What about mechanical

    Photo 3: Gaps between the roof insulation and roof edges, curbs and penetrations are prevalent on most roofing projects and should be sealed with spray foam insulation as seen here. It will be trimmed flush once cured.

    equipment? Photovoltaic panels? Yes, we have designed roofs in which a forklift had to go between penthouses across the roof. Understanding how the roof will be used will help you immensely.

  2. Understand the construction process and how the roof might be used during construction. It is amazing how few architects know how a building is built and understand construction sequencing and the impact it can have on a roof. I firmly believe that architects think that after a lower roof is completed, that the masons, carpenters, glazers, sheet metal workers, welders, pipe fitters, and mechanical crews take time to fully protect the newly installed systems (often of minimal thickness and, here we go again, without a cover board — OMG) before working on them. I think not. Had the architect realized that temporary/vapor retarders could be installed as work surfaces, getting the building into the dry and allowing other trades to trash that rather than the finished roof, the roof system could be installed after those trades are off the roof.
  3. Coordinate with other disciplines. Roof systems cannot be designed in a vacuum. The architect needs to talk to and involve the structural, mechanical and plumbing engineers to ensure they realize the importance of essential details. For example, we cannot have steel angle around the drain whose flange rests on the bar joist, thus raising the roof deck surface at the roof drain. Ever wonder why you had ponding at the drain? Now you know. I attempt to always have a comprehensive, specific roofing detail on the structural, mechanical and plumbing sheets. I give the other disciplines my details and ask that they include them on their drawings, changing notes as required. That way, my 20-inch roof curb on the roof detail is a 20-inch curb on the mechanical sheets — not a standard 12-inch curb, which would more often than not be buried in insulation.
  4. Detail, detail, detail, and in case you glossed over this section, detail again. Make sure to include job-specific, clearly drawn details. Every condition of the roof should be detailed by the architect. Isn’t that what the client is paying for? Do not, as I once saw, indicate “RFO” on the drawings. Yes, that acronym stands for “Roofer Figure Out.” Apparently, the roofer did not figure it out. I enjoyed a nice Hawaiian vacation as a result of my work on that project, courtesy of the architect’s insurance company. How do you know that a condition works unless you design it and then draw it to scale?

    Figure 4: Insulation to curbs, roof edge and penetrations will not be tight, and to prevent a thermal short, the gaps created in construction need to filled with spray foam, as noted and shown here in this vent detail. Photos: Hutchinson Design Group

    I’ve seen roof insulation several inches above the roof edge because, OMG, the architect wanted gravel stop and forgot about camber. Not too big a deal (unless of course it’s a large building) to add several more layers of wood blocking and tapered edge strips at the now high wood blocking in the areas that were flush, but now the face of the roof edge sheet metal needs to increase. But what if the increase is above the allowable ANSI-SPRI ES1 standard and now a fascia and clip are required? You can see how the cost spirals, and the discussion ensues about who pays for what when there is a design error.

  5. Develop comprehensive specifications that indicate how the roof system components are to be installed. This requires empirical knowledge, the result of time on the roof observing construction. It is a very important educational tool that can prevent you, the designer, from looking like a fool.

Components

Best practices for single-ply membranes, in addition to the design elements above, also involve the system components. Below is a listing of items I feel embodies best practices for single-ply roof system components:

  1. Thicker membranes: The 45-mil membrane is insufficient for best practices, especially when one considers the thickness of the waterproofing over scrim on reinforced sheets. A 60-mil membrane is in my opinion the best practices minimum. Hear that? It’s the minimum. You are allowed to go to 75, 80 or 90 mils.
  2. Cover boards: A cover board should be specified in fully adhered and mechanically attached systems. (Ballasted systems should not incorporate a cover board.) Cover boards have enhanced adhesion of the membrane to the substrate over insulation facers and hold up better under wind load and hail. Cover boards also protect the insulation

    Photo 4: The greatest concern with the use of polyurethane adhesives is that the insulation board might not be not fully embedded into the adhesive. Weighting the boards at the corners and center with a minimum of 35 pounds for 10 minutes has proven to work well in achieving a solid bond.

    from physical damage and remain robust under foot traffic, while insulation tends to become crushed. Cover boards are dominated by the use of mat-faced modified gypsum products. Hydroscopic cover boards such as fiberboards are not recommended.

  3. Insulation: Now here is a product that designers seldom realize has many parts to be considered. First, let’s look at compression strength. If you are looking to best practices, 25 psi minimum is the way to go. The 18-psi insulation products with a fiber reinforced paper facer can be ruled out entirely, while 20 psi products are OK for ballasted systems. Now let’s look at facers. If you think about it for a second, when I say “paper-faced insulation,” you should first think “moisture absorbing” and secondly “mold growth.” Thus paper-faced products are not recommended to be incorporated if you are using best practices. You should be specifying the coated glass-faced products, which are resistant to moisture and mold resistant. A note to the manufacturers: get your acts together and be able to provide this product in a timely manner.

Additional considerations regarding insulation:

  • Insulation joints and gaps: You just can’t leave joints and gaps open. Show filling the open joints at the perimeter and curbs and around penetrations with spray foam in your details and specify this as well (see Photo 3 and Figure 4).
  • Mechanical attachment: Define the method of attachment and keep it simple. On typical projects, I commonly specify one mechanical fastener every 2 square feet over the entire roof (unless more fasteners are needed in the corners). Reducing the number of fasteners in the field compared to the perimeter can be confusing for contractors and the quality assurance observer, especially when the architect doesn’t define where that line is. The cost of the additional screws is nominal compared with the overall cost of the roof.
  • Polyurethane foam adhesive: Full cover spray foam or bead foam adhesive is taking over for asphalt, at least here in the Midwest, and I suspect in other local markets as well. The foam adhesive is great. It sticks to everything: cars, skylights, clerestories, your sunglasses. So, it is amazing how many insulation boards go down and don’t touch the foam. You must specify that the boards need to be set into place, walked on and then weighted in place until set. We specify five 35-pound weights (a 5-gallon pail filled with water works nicely), one at each corner and one in the middle for 10 minutes (see Photo 4). Yes, you need to be that specific.
  1. Photo 5: The design of exterior walls with metal studs that project above the roof deck is a multi-faceted, high-risk detail that is often poorly executed. Here you can see a gap between the deck and wall through which warm moist air will move and result in the premature failure of this roof. The sheathing on the wall cannot hold the horizontal base anchor screw, and the joints in the board allow air to pass to the base flashing, where is will condense. This is the type of architectural design that keeps on giving — giving me future work.

    Vapor/air barrier: A vapor air barrier can certainly serve more than a function as required for, say, over wet room conditions: pools, locker rooms, kitchens, gymnasiums. We incorporate them in both new construction and re-roofing as a means of addressing construction trade phasing and, for re-roofing, allowing time for the proper modification of existing elements such as roof edges, curbs, vents, drains, skylights and pipe curbs. Be sure to detail the penetrations and tie-ins with wall components.

  2. Deck type: Robust roof decks are best. Specify 80 ksi steel roof decks. Try staying away from joint spacing over 5 feet. Decks should be fully supported and extend completely to roof edges and curbs.
  3. Roof edge design: A key aesthetic concern, the termination point for the roof system, the first line of defense in regard to wind safety — the roof edge is all of these. The construction of the roof edge on typical commercial construction has changed drastically in the last 20 years, from brick and block to metal stud. Poorly designed metal stud parapets will be funding my grandkids’ college education. The challenge for the metal stud design is multifaceted: It must close off the chimney effect, prevent warm moist air from rising and condensing on the steel and wall substrate, create an acceptable substrate on the stud face in which to accept base anchor attachment, and — oh, yes — let’s not forget fire issues. Tread lightly here and create a “big stick” design (see Photo 5).
  4. Roof drains and curbs: As discussed above, there is a great need for coordination and specific detailing here. The rewards will be substantial in regard to quality and efficiency, minimizing time spent dealing with “what do we do now” scenarios.
  5. Slope: Design new structures with structural roof deck slope, then fine tune with tapered insulation.

Final Thoughts

Best practices will always be a balancing act between cost and quality. I believe in the mantra of “doing it right the first time.”

The industry has the material and contractors possess the skill. It’s the design and graphic communication arm that needs to improve to keep everyone working at the top of their game.

Designers, get out in the field and see the results of your details. See firsthand how a gypsum-based substrate board on a stud wall does not hold screws well; how a lap joint may not seal over the leading edge of tapered insulation; how the roof either ponds water at the roof drain or doesn’t meet code by drastically sumping; or how the hole cut in the roof membrane for the drain might be smaller than the drain bowl flange, thus restricting drainage. Seeing issues that the contractors deal with will help you as the designer in developing better details.

Contractors, when you see a detail that doesn’t work during the bidding, send in an RFI and not only ask a question, but take the time to inform the architect why you don’t think it will work. On a recent project here in Chicago, the architect omitted the vapor retarder over a pool. The contractor wrote an explicit explanation letter and RFI to the architect during bidding, and the architect replied, “install as designed.” In these situations, just walk away. For me, this is future work. A local contractor once told me, “I don’t get paid to RFI, I get paid to change order.” He also said, “If I ever received a response to an RFI, I would frame it!”

Manufacturers, too, can raise the bar. How about prohibiting loose base flashings at all times, and not allowing it when the salesman says the competition is allowing it. Have contractors on the cusp of quality? Decertify them. You don’t need the hassles. Owners don’t need the risk.

Seek out and welcome collaboration among contractors, roof systems designers, knowledgeable roof consultants, and engineers. Learning is a lifelong process, and the bar is changing every year. Too often we can be closed off and choose not to listen. At HDG, I am proud to say we have the building owners’ best interests at heart.

By all working together, the future of single-ply membranes can be enhanced and the systems will be retained when the next generation of roof cover arrives — and you know it will.

Roofing in Romania, Part II: Past as Prologue

[Editor’s Note: In May, Thomas W. Hutchinson presented a paper at the 2017 International Conference on Building Envelope Systems and Technologies (ICBEST) in Istanbul, Turkey, as did his good friend, Dr. Ana-Maria Dabija. After the conference, Hutchinson delivered a lecture to the architectural students at the University of Architecture in Bucharest, Romania, and spent several days touring Romania, exploring the country’s historic buildings and new architecture. Convinced that readers in the United States would appreciate information on how other countries treat roofing, he asked Dr. Dabija to report on roof systems in Romania. The first article, “Roofing in Romania: Lessons From the Past,” was published in the July/August issue of Roofing. In this follow-up article, Dr. Dabija continues her exploration of the forces shaping the architecture of Romania.]

A late 19th or early 20th century residential building in Bucharest. Photo: Ana-Maria Dabija.

(Photo 1) A late 19th or early 20th century residential building in Bucharest. Photo: Ana-Maria Dabija.

In buildings as well as in other fields of activity, there are at least three determinant factors in the choice of products:

  1. The technology. A key driving force is the technology that improves a product or system. Some systems are not at all new—the ones that use solar power, for instance—but are periodically forgotten and rediscovered; this is another story. The history of past performance is important here as well, as is the skill of the contractors installing the material or system. Technological advancements can mark important developments in industry, but the field is littered with “new and improved” products that never panned out, failed and are out of the market.
  2. The economy. The state of the economy is directly related to the state of the technology; better efficiency in the use of a type of resource leads to the use of more of that resource, as well as to a change of human behavior that adapts to the specific use of the resource. This dynamic is referred to as “the Jevons paradox” or “the rebound effect.” In a nutshell, William Stanley Jevons observed, in his 1865 book “The Coal Question,” that improvements in the way fuel is used increased the overall quantity of the utilized fuel: “It is a confusion of ideas to suppose that the economical use of fuel is equivalent to diminished consumption. The very contrary is the truth.” On the other hand, it seems that innovation is mainly accomplished in periods of crisis, as a crisis obliges one to re-evaluate what one has and to make the best of it.
  3. The political will. As one of the great contemporary architects, Ludwig Mies van der Rohe, stated, “Architecture is the will of the epoch translated into space.”

Like many other things, buildings can be read from the perspective of these factors. And so we go back to square one: history.

(Photo 2) Palace of the National Bank of Romania (1883-1900), designed by architects Cassien Bernard, Albert Galleron, Grigore Cerkez, and Constantin Băicoianu. Photo: Ana-Maria Dabija.

Our excursion in the history of the roofing systems in Romania moves from the 19th century to the present. As mentioned in the previous article, the use of metal sheets and tiles began sometime in the late 17th century (although lead hydro-insulation seems to have been used in the famous Hanging Gardens of Babylon in the sixth or seventh century, B.C.).

The Industrial Revolution that spread from the late 18th to the mid 19th century included the development of iron production processes, thus leading to the flourishing of a new range of building materials: the roofing products. The surfaces that can be covered with metal elements—tiles or sheets—span from low slopes to vertical. More complicated roofs appeared, sometimes combining different systems: pitched or curved roofs use tiles while low slopes are covered with flat sheets.

Copper, painted or galvanized common metal, zinc or other alloys cut in tiles and sheets, with different shapes or fixings—the metal roofs of the old buildings are a gift to us, from a generation that valued details more than we do, today (Photo 1).

(Photo 3) The Palace of the School of Architecture in Bucharest, designed by architect Grigore Cerchez. Photo: Ana-Maria Dabija.

In the second half of the 19th century, in 1859, two of the historic Romanian provinces—Walachia and Moldova—united under the rule of a single reigning monarch, and, in 1866, a German prince, Karl, from the family of Hohenzollern, became king of the United Principalities. In 1877 the War of Independence set us free from the Turkish Empire and led to the birth of the new kingdom of Romania. The new political situation led to the need of developing administrative institutions as well as cultural institutions, which—in their turn—needed representative buildings to host them. In only a few decades these buildings rose in all the important cities throughout the country.

The influence of the French architecture style is very strong in this period as, in the beginning, architects that worked in Romania were either educated in Paris or came from there. It is the case with the Palace of the National Bank of Romania (Photo 2), designed by two French architects and two Romanian ones.

(Photo 4) A detail of the inner courtyard and roof at the Central School by architect Ion Mincu, 1890. Photo: Ana-Maria Dabija.

The end of the 19th century is marked by the Art Nouveau movement throughout the whole world, with particular features in architecture revealing themselves in different European countries. In Romania, the style reinterprets the features of the architecture of the late 1600s, thus being called (how else?) the Neo-Romanian style. A few fabulous examples of this period that can be seen in Bucharest include the Palace of the School of Architecture (Photo 3), the Central School (Photo 4), the City Hall (Photo 5). Most of the roofs of this period use either clay tiles or metal tiles and metal sheets (Photos 6 and 7).

In parallel with the rise of the Art Nouveau style in Europe, the United States created the Chicago School, mainly in relation to high-rise office buildings. This movement was reinterpreted in the international Modernist period (between the two World Wars).

As a consequence of the Romanian participation in the First World War, in 1918 Basarabia (today a part of the Republic of Moldova, the previous Soviet state of Moldova), Bucovina (today partly in Ukraine) and Transylvania were united with Romania. The state was called Greater Romania. The capital city was Bucharest. Residential buildings as well as administrative buildings spread on both sides of the grand boulevards of the thirties, built in a genuine Romanian Modernist style (Photo 8).

(Photo 5) Bucharest City Hall, by architect Petre Antonescu 1906-1910. Photo Joe Mabel, Creative Commons Attribution.

Influences from the Chicago School are present in the roof types. Flat roofs began to be used, sometimes even provided with roof gardens (although none have survived to our day). It is probable that the hydro-insulation was a “layer cake” of melted bitumen, asphalt fabric and asphalt board, everything topped with a protection against UV and IR radiation. The “recipe” was mostly preserved and used until the mid-90s.

In the second half of the 20th century, the most common roofs were the bitumen membranes, installed layer after layer. Residential buildings and most administrative buildings had flat roofs. Still, in the center of the cities, more elaborate architecture was designed, so next to a church with a metallic roof, you might find a residential block of flats with pitched roofs covered with metal tiles, behind which the lofts are used as apartments (Photo 9).

Most of the urban mass dwellings, however, were provided with flat roofs (Photo 10). Even the famous House of the People (Photo 11)—the world’s second-largest building after the Pentagon—has flat roofs with the hydro-insulation made of bitumen (fabric and board layers).

(Photo 6) Residential buildings built in the late 19th or early 20th century in the center of Bucharest. Photo: Ana-Maria Dabija.

Corrugated steel boards or fiberboards were mainly used in industrial buildings and sometimes in village dwellings, replacing the wooden shingles as a roofing solution that could be easily installed (Photo 12).

After 1989, when the communist block collapsed, products from all over the world entered the market. The residential segment of the market exploded, as wealthy people wanted to own houses and not apartments. Pitched roofs became an interesting option, and the conversion of the loft in living spaces was also promoted. Corrugated steel panels, with traditional or vivid colors, invaded the roofs, serving as a rapid solution both for new and older buildings that needed to be refurbished. Skylights, solar tunnels and solar panels also found their way onto the traditional roofs as the new developments continued (Photo 13).

Today the building design market is mainly divided between the residential market and the office-retail market. Where roofs are concerned, unlike the period that ended in 1989 (with a vast majority of buildings with flat roofs, insulated with bitumen layers), most individual dwellings and collective dwellings with a small number of floors (3-4) are provided with pitched roofs, mainly covered with corrugated steel panels.

(Photo 7) The Minovici Villa, architect Cristofi Cerchez, 1913. Photo: Camil Iamandescu, Creative Commons Attribution.

For the high-rise buildings, the bitumen membranes (APP as well as SBS) are still the most common option, but during the past decade, elastomeric polyurethane and vinyl coatings have also been installed, with varying degrees of success. EPDM membranes, more expensive than the modified bitumen ones, are used on a smaller scale. PVC membranes have also been a choice for architects, as in the case of the “Henry Coandă” Internațional Airport in Bucharest. Bitumen shingles also cover the McDonalds buildings and other steep-slope roofs. In the last few years, green roofs became more interesting so, more such solutions are beginning to grow on our buildings.

The roof is not only the system that protects a building against weathering; today it is an important support for devices that save or produce energy. It will always be the fifth façade of the building, and it will always represent a water leakage-sensitive component of the envelope that should be dealt with professionally and responsibly. To end the article with a witty irony, the great American architect Frank Lloyd Wright is supposed to have said, “If the roof doesn’t leak, the architect hasn’t been creative enough.”

(Photo 8) The Magheru Boulevard in Bucharest. Photo: Ana-Maria Dabija.

(Photo 9) Apartment buildings of the late 20th century in Bucharest. Photo: Ana-Maria Dabija

(Photo 10) Mass dwelling building of the mid-1980s. Photo: Ana-Maria Dabija.

(Photo 11) The House of the People (today the House of the Parliament) is still unfinished. The main architect is Anca Petrescu. Photo: Mihai Petre, Creative Commons Attricbution CC BY-SA 3.0.

(Photo 12) Corrugated fiberboard on a traditional house in the Northern part of Romania. Photo: Alexandru Stan.

(Photo 13) The roof of the historic building of the Palace of the School of Architecture, with skylights, sun tunnels and BIPV panels. Photo: Silviu Gheorghe.

Roofing in Romania: Lessons From the Past

[Editor’s Note: In May, Thomas W. Hutchinson presented a paper at the 2017 International Conference on Building Envelope Systems and Technologies (ICBEST) in Istanbul, Turkey, as did his good friend, Dr. Ana-Maria Dabija. After the conference, Hutchinson delivered a lecture to the architectural students at the University of Architecture in Bucharest, Romania, and spent several days touring Romania, exploring the country’s historic buildings and new architecture. Convinced that readers in the United States would appreciate information on how other countries treat roofing, he asked Dr. Dabija to report on roof systems in Romania in the first of what is hoped to be a series of articles on roofing in foreign countries.]

Photo 1. Sanctuary in Sarmizegetusa Regia. Photo: Oroles. Public Domain.

Photo 1. Sanctuary in Sarmizegetusa Regia. Photo: Oroles. Public Domain.

Romania is somewhere in the Southeastern part of Europe, in a stunning landscape: an almost round-shaped country, with a crown of mountains—Carpathians—that close the Transylvanian highlands, with rivers that flow towards the plains, that merge into the Danube and flow to the Black Sea.

Conquered by the Romans in 106 A.D, crossed by the migrators between the fourth and the eighth centuries, split in three historic provinces—Walachia, Moldova and Transylvania—and squeezed between empires, Romania absorbed features from all the people and civilizations that passed through or stayed in its territories.

The language—Latin in its structure—has ancient Dacian words that blend in with words from languages from other countries that had influence in our history: Greek, French, Turkish, English, Slavonic, Serbian, German, Hungarian. Traditional foods vary by region; for instance, in Transylvania you won’t find fish, while at the seaside, in the Danube Delta, on the banks of the rivers, fish is traditional. Each historic province uses different ingredients and developed recipes that can be found in Austria and Hungary, in Greece and Turkey, in Russia and Ukraine.

The same applies to buildings. In Transylvania, the Austrian Empire hallmarked the houses in the villages, the mansions, the palaces, the churches, the administrative buildings. One of the most popular sites for foreign tourists is the Bran Castle, infamous home of Dracula. In Walachia, the buildings have strong Balkan influences. Close to the Black Sea, the Turkish and the Greek communities that settled there brought the style of the countries they came from. Moldova was under the influence of the Russian Empire reaching back to Peter the Great.

Photo 2. Densuș church, Hațeg County, has a roof made of stone plates. Photo: Alexandru Baboș, Creative Common Attribution.

Photo 2. Densuș church, Hațeg County, has a roof made of stone plates. Photo: Alexandru Baboș, Creative Common Attribution.

Romania is situated in the Northern hemisphere, about halfway between the Equator and the North Pole. The climate features hot, dry summers with temperatures that can rise to 113 degrees Fahrenheit in the South, and cold winters, with temperatures that can drop to minus 22 degrees in the depressions of Transylvania, with heavy snow and strong winds. There are some spots with milder temperatures, close to the sea and in the western part of the country.

Why all this introduction? Because specific geographic conditions lead to specific building systems. People living in areas with abundant rain and snow need materials and systems that resist and shed water; after all, the steeper the slope, the faster the water is evacuated off the roof.

Cultural influences color the patrimony, but climatic conditions define the geometry and the materials that are used for roofs. As there are different climatic conditions as well as diverse cultural influences, the building typologies of the roofs are, in their turn, diverse.

Ancient Settlements

Photo 3. Below-ground cottage in the Village Museum in Bucharest. Photo: Ana-Maria Dabija.

Photo 3. Below-ground cottage in the Village Museum in Bucharest. Photo: Ana-Maria Dabija.

Although these territories were inhabited for millennia, the roofs did not “travel” in time as long as the walls. The six ancient citadels of the Dacians, located almost in the center of Romania in the southwestern side of the Transylvanian highlands, still preserve ruins of the limestone, andesite or wooden columns of the shrines, altars, palaces and agoras. No roofs survived. (See Photo 1.) We can only presume that the materials that were used for the roofing were wood shingles or thatch, which would explain both why artefacts of the roofs could not be found and also why the deterioration is so advanced.

After Rome conquered Dacia, emperor Trajanus built a citadel that was supposed to represent continuity with the previous civilization: the Sarmizegetusa Ulpia Traiana. It seems to have had an active life, considering the temples, palaces and dwellings that we inherited, including an amphitheater for 5,000 people. Still, no roofing traces survived.

Pages: 1 2 3 4 5

Roof Rot: Ignorance Is an Easy Way to Damage Low-slope Residential Roofs

Change often brings with it unintended consequences, and the issue of reflective roof surfaces in North America is no exception. In the late 1990s, U.S. cities in northern climates started to mandate the use of reflective roof—more for politics, feel-good, pseudo-environmental reasons than sustainable, resilient and durable reasons. In my estimation, cool roofs often did more to lower the quality of buildings than enhance them. Furthermore, code and standard changes were made with no understanding of the result and no education to the architects of America.

Figure 1: Reduced attic space resulted in a roof section comprised of the following components from the interior to the roof cover.

Figure 1: Reduced attic space resulted in a roof section comprised of the following components from the interior to the roof cover.

Although the resulting unintended consequences affected commercial and residential buildings, it was the often-catastrophic results on low-slope residential buildings that went untold and left homeowners with tens of thousands of dollars of corrective work on basically new residences.

Following is a summary of how these concerns evolved in wood-framed residential construction. I’ve included case studies of failures, potential solutions and lessons learned.

HISTORY

During the industrialization of America’s large cities throughout the 1800s, the need for labor caused populations to explode. To house the labor migration, row houses (3- to 4-story structures, often with a garden level and four or more narrow units) were constructed approximately 3-feet apart, block after block, creating medium-sized apartment blocks. Most of these row houses were wood-framed, masonry veneer with low-slope roof structures. The interior walls and ceilings were finished in cementitious plaster, which provided a durable, fire-resistive finish. The plaster also performed as an effective air and vapor barrier, preventing interior conditioned air from penetrating into the non-insulated walls and ceilings where it could condense within the walls and roof on cold days.

Photo 1: A contractor was called out to fix the “soft roof” and found this catastrophic situation.

Photo 1: A contractor was called out to fix the “soft roof” and found this catastrophic situation.

Heating costs were low, so little—if any—insulation was installed in the walls and roof. Roofs were composed of built-up asphalt and coal tar, both smooth and aggregate surfaced. Attic spaces often 4 to 6 feet in height were vented via static vents. Any conditioned air that passed to the attic was able to dissipate through these static vents. This method of construction performed without significant attic condensation, and the roof systems and roof structure served these buildings for decades.

In the mid 1990s, researchers (theoretical researchers with no architectural, engineering, roofing, construction or practical building technology experience or knowledge) at research institutes conducted studies into the effects of minimizing solar gain through the roof via a reflective surface. Based on the researchers’ algorithmic findings and recommendations (regardless of their validity), environmental groups used the concept to promote change. Large cities started introducing new energy codes with reflective roofing requirements and prescribed reflectance values. These new codes contained greater insulation requirements, which was a benefit. However, in this one code adoption, roof systems, such as coal-tar pitch, that had performed for centuries were no longer permitted. Consequently, roofing contractors went out of business and so did some roofing material manufacturers because of unproven and suspect research.

Photos and Details: Hutchinson Design Group Ltd.

Pages: 1 2 3 4

Architects and Roof System Designers: Your Details and Drawings Are Seriously Lacking Design Intent

Dear Mr. and Ms. Architect and Roof System Designer:
The following are comments I hear over and over:

  • “Seventy-five percent of the time I cannot determine what roof assembly an architect wants from a spec.”
  • “One always feels they have to play private detective and try to figure out what [a roof system designer] actually wants.”

As an architect and registered roof consultant, I take great pride in my roof system designs and detailing, which are project specific, at minimum meet the code, and more often than not exceed code with all conditions and building components that impinge on the roof detailed for the specific project. In listening to construction managers, general contractors, roofing contractors and suppliers talk, you would think that architects barely know that the roof is on top of the building! It seems most do not even have basic knowledge and certainly don’t know when water may flow uphill. This is embarrassing to hear! It starts in the university with the curriculum placing all emphasis on building design and not how to actually construct a building. In many ways, this is good for my firm as we are busy fixing what should never have required fixing.

Peer review of several projects designed by very large (and what you would assume to be very sophisticated firms) and even small boutique firms reveals the following:

A. The roof system design is not code compliant in regard to tapered insulation.

B. The roof system itself is not code compliant, but contract documents require “contractor to verify or be responsible for code compliance”. This begs the question: Who is being paid to design? Is it the architect or the contractor?

C. Structural and, especially, structural lightweight concrete pose significant roofing challenges and architects have no clue about that, resulting in roof systems in danger of imminent failure.

D. The accuracy of construction documents in general is very, very low. Even I cannot often determine what roof assembly an architect wants from a specification.

  • 1. For example, architects do not list products in the specs that will be used in the assembly.
  • 2. Substrate boards, cover boards and vapor barriers are frequently listed in the specs but never shown on the plan.

E. The detailing of wall air barriers to roof vapor or air barriers is not shown and certainly no definition of responsibility prescribed as to who is to tie these materials together.

F. Understanding of material limitations is non-existent.

  • 1. Weather, wind, cold, snow, humidity and temperature affect the installation of roof system components. I especially get a kick out of seeing water-based adhesives being specified for construction taking place in winter; this means future work for my firm.

G. Roof edges and how they terminate at high walls is never detailed.

H. Roof drains and curbs are improperly or not detailed.

I. Specifications are inadequate—often boilerplate generic—and do not match the drawings. I’ve also seen non-specific details that are not to scale or do not reflect actual conditions.

  • 1. Design wind speed is not given when appropriate.
  • 2. Warranty requirements are in- correct, not thought-out or not specified at all.

J. Architects or consultants sometimes have multiple designs listed in the specification, leaving it to the con- tractor to issue RFIs that, more often than not, are not answered.

  • 1. These inconsistencies lead to frustration and, in many cases, the contractors just decide it is not worth the time or effort to even bid the project or add a good deal of money to cover undefined items.

K. I’ve witnessed owners who have hired professionals to design build- ings costing hundreds of millions of dollars, and yet these “professionals” often do not exhibit the standard of care expected.

  • 1. Poor designs compound when met with an irresponsible contractor who will not do his or her due diligence and investigate what is needed to install a quality system.

Illustrations: courtesy of Hutchinson Design Group Ltd.

Pages: 1 2 3 4

The Integration of Roof and Brick Requires Concise Details

PHOTO 1: The through-wall flashing stainless-steel drip can be observed projecting nicely from the wall—but the termination of the roof base flashing more than 1-inch below resulted in a section of the brick wall that allows water to pass into the wall below the through-wall flashing and behind the roof base flashing, resulting in the damage seen in Photo 2.

PHOTO 1: The through-wall flashing stainless-steel drip can be observed projecting nicely from the wall—but the termination of the roof base flashing more than 1-inch below resulted in a section of the brick wall that allows water to pass into the wall below the through-wall flashing and behind the roof base flashing, resulting in the damage seen in Photo 2.

Projects are perceived to be successful by their ability to prevent disturbance from weather, including rain. Have you ever heard two architects talking about Frank Lloyd Wright?

“What a genius! His spatial conception is magnificent, even after 100 years.”

“But all his buildings leak!”

I used to give a talk to University of Illinois architecture students in which I told them the quickest way to go out of business is to be sued. The quickest way to be sued is to have a building allow moisture intrusion. If he were alive today, Frank Lloyd Wright—God rest his soul—would be in jail (and a few current architects may be well on their way). Owners are not very kind when their “babies” leak.

Many roof termination interfaces are never even thought about by designers and are left to the roofing contractor to work out. This is not a recommended practice. One such condition—that every architect should be able to detail—is how the roof base flashing terminates at a masonry wall that has through-wall flashing and weeps at the base of the wall above the roof. I believe so fervently that architects should be proficient in detailing these conditions that I believe it should be required to procure their license.

WHY THE IMPORTANCE

The interface of roof base flashing and masonry through-wall systems occurs on a majority of commercial construction projects. If this transition is not performed correctly, moisture intrusion behind the roof base flashing to the interior will occur (see Photo 2). When this occurs, besides angering owners, it befuddles the architect. Photo 1 (left) shows a nice through-wall flashing drip extended out from the wall, weeps and roofing terminated with a termination bar and sealant. What could be wrong?

PHOTO 2: Moisture intrusion at the base of this wall was the result of water circumventing the through-wall flashing and roof base flashing termination seen in Photo 1. A big concern with conditions, such as this, is the propensity of the materials to promote mold growth.

PHOTO 2: Moisture intrusion at the base of this wall was the result of water circumventing the through-wall flashing
and roof base flashing termination seen in Photo 1. A big concern with conditions, such as this, is the propensity of the materials to promote mold growth.

The exposed brick above the termination bar and below the stain- less-steel drip of the through-wall flashing is susceptible to water flowing down the surface of the brick. Water passing through the brick above is supposed to be weeped out; however, at the exposed brick above the termination bar, the water moves into the wall and has nowhere to go but inward.

The cost to repair these conditions can be, depending on the conditions, expensive. Repairs often require brick removal and through-wall flashing mitigation. In this particular case, be- cause there is a stainless-steel drip, my team recommended a stainless-steel counterflashing be pop-riveted to the drip and extended over the termination bar.

CHALLENGES

Why is the interface of roof base flashing and masonry through-wall systems so difficult for architects and roof consultants to detail? I believe it is because they have no clue it needs to be detailed as an interface, especially because detailing of appropriate through-wall systems is so sporadic. I endeavor in this article to change at least the knowledge part.

The detailing of this condition not only requires the ability to interface two building systems, but also requires considerable time to ensure specification of wall sectional details and roofing details are appropriately placed where the responsible trades will see them.

PHOTO 3: Still under construction, the stainless-steel counterflashing has been installed. The roof base flashing will terminate below the stainless-steel counterflashing receiver. Hutch prefers brick below the through-wall flashing and above the roof deck, though the masonry mortar joints below the through-wall flashing should have been struck flush.

PHOTO 3: Still under construction, the stainless-steel counterflashing has
been installed. The roof base flashing will terminate below the stainless-steel counterflashing receiver. Hutch prefers brick below the through-wall flashing and above the roof deck, though the masonry mortar joints below the through-wall flashing should have been struck flush.

NEW CONSTRUCTION

New construction provides us a clean slate to “do it right the first time”. The first order of business is to determine the height of the base flashing. This can be tricky with tapered insulation and slope structures with saddles. Let’s consider the following examples (see Detail 4, page 3):

EXAMPLE 1
We are dealing with a flat roof, tapered insulation, cover board and bead-foam insulation in ASHRAE Climate Zone 5, which has an R-30 minimum.

  • The roof drain is 32-feet away from the wall. Code requires 5.2 inches of insulation at 4 feet from the drain, so let’s assume 5 inches at the drain.
  • 1/4-inch tapered starts at 1/2 inch at 32 feet. That’s 8 inches, plus the starting thickness of 1/2 inch, which equals 8 1/2 inches.
  • Cover-board thickness is 1/2 inch.
  • Bead foam thickness is 3/16 inch for each layer. Let’s assume five layers, so 1 foot of bead foam.
  • Thus, the surface of the roof at the wall will be 15 inches above the roof deck.

Because you would like to work at the masonry coursing level and given that concrete masonry units (CMU) are nominal 8 inches, you are looking at placing the through-wall flashing 24 inches above the roof deck.

This 24-inch dimension of where to place the through-wall flashing needs to be placed on the building section and/or wall section because the mason, which will be onsite prior to the roofing contractor, will need to know this information.

This 24-inch height begs another termination question: What occurs at the roof edge with this height? Hold that thought for now. Terminations at intersections will be discussed in future articles.

Pages: 1 2 3

Code-mandated Thermal Insulation Thicknesses Require Raising Roof Access Door and Clerestory Sill Details

PHOTO 1: The new roof has been installed at SD 73 Middle School North and it can clearly be seen that the door and louver need to be raised. On this project, there were four such conditions.

PHOTO 1: The new roof has been installed at SD 73 Middle School North and it can clearly be seen that the door and louver need to be raised. On this project, there were four such conditions.

The most common concern I hear related to increasing insulation thickness (a result of increased thermal values of tapered insulation), especially in regard to roofing removal and replacement, is, “OMG! What about the roof access door and/or clerestory?” You can also include, for those knowledgeable enough to consider it, existing through-wall flashing systems and weeps.

I’m a bit taken aback by this concern; I have been dealing with roof access doors and clerestory sills for the past 30 years and, for the most part, have had no problems. My first thought is that roof system designers are now being forced to take these conditions seriously. This is a big deal! They just have no clue.

In the next few pages, I’ll review several possible solutions to these dilemmas, provide some detailing suggestions and give you, the designer, some confidence to make these design and detailing solutions. For the purpose of this article, I will assume reroofing scenarios where the challenge is the greatest because the conditions requiring modification are existing.

THE ACCESS DOOR

For many and perhaps most contractors who sell and, dare I say, design roofs, it is the perceived “large” expense of modifying existing conditions that is most daunting. Often, these conditions are not recognized until the door sill is several inches below the new roof sur- face. Not a good predicament. Planning for and incorporating such details into the roof system design will go a long way to minimizing costs, easing coordination and bringing less tension to a project.

PHOTO 2: The sill has been raised and new hollow metal door, frame and louver have been installed at SD 73 Middle School North. Door sill and louver sill flashing are yet to be installed, as are protective rubber roof pavers.

PHOTO 2: The sill has been raised and new hollow metal door, frame and louver have been installed at SD 73 Middle School North. Door sill and louver sill flashing are yet to be installed, as are protective rubber roof pavers.

Door access to the roof is the easiest method to access a roof. These doors are typically off a stair tower or mechanical penthouse and most often less than 12 inches above the existing roof as foresight was not often provided (see photos 1, 2 and 6 through 9). With tapered insulation thickness easily exceeding 12 inches, one can see that door sills can be issues with new roof systems and need to be considered.

Designers should first assess the condition of the door and frame, typically hollow metal. Doors and frames that are heavily rusted should not be modified and reused, but discarded, and new ones should be specified. The hardware too needs to be assessed: Are the hinges free of corrosion and distortion? Is the closure still in use or detached and hanging off the door frame? The condition of door sweeps, knobs, lockset and weather stripping should also be determined. Ninety-nine percent of the time it is prudent to replace these parts.

As the roof system design develops, the designer should start to get a feel for the thickness of insulation at the door. It is very important the designer also consider the thicknesses that vapor retarders, bead and spray-foam adhesives, cover and board and protective pavers will add. These can easily be an additional 4 inches.

PHOTO 3A: The new roofing at SD 73 Elementary North was encroaching on this clerestory sill and required that it be raised. As part of this project, the steel lintel was exposed. It was prepped, primed and painted and new through-wall flashing was installed.

PHOTO 3A: The new roofing at SD 73 Elementary North was encroaching on this clerestory sill and required that it be raised. As part of this project, the steel lintel was exposed. It was prepped, primed and painted and new through-wall flashing was installed.

Once the sill height is determined, the design of the sill, door and frame can commence. If the sill height to be raised is small—1 1/2 to 3 inches—it can often be raised with wood blocking cut to fit the hollow metal frame, flashed with the roofing membrane, metal sill flashing and a new door threshold installed, and the door and frame painted. This will, of course, require the removal of the existing threshold and door which will need to be cut down to fit and then bottom-sealed with a new metal closure (see details A and B, page 3).

When the door sill needs to be raised above 3 inches, the design and door considerations increase. Let’s consider that the door and frame is set into a masonry wall of face brick with CMU backup. Although most hollow metal doors are 7 feet 2 inches to match masonry coursing, after the modification the door may be shorter. For example, if a door is 7 feet 2 inches and you must raise the sill 5 inches, the new door and frame will need to be 6 foot 9 inches.
PHOTOS & ILLUSTRATIONS: Hutchinson Design Group Ltd.

Pages: 1 2 3

Concise Details and Coordination between Trades Will Lead to a Quality Long-term Solution for Roof Drains

PHOTO 1: Roof drains should be set into a sump receiver provided and installed by the plumbing contractor.

PHOTO 1: Roof drains should be set into a sump receiver provided and installed by the plumbing contractor.

The 2015 IECC roof thermal insulation codes have forced roof system designers to actually think through the roof system design rather than rely on generic manufacturers’ details or the old built-up roof detail that has been used in the office. Don’t laugh! I see it all the time. For the purpose of this article, I will deal with new construction so I can address the coordination of the interrelated disciplines: plumbing, steel and roof design. In roofing removal and replacement projects, the process and design elements would be similar but the existing roof deck and structural framing would be in place. The existing roof drain would need to be evaluated as to whether it could remain or needs to be replaced. My firm typically replaces 85 percent of all old roof drains for a variety of reasons.

The new 2015 IECC has made two distinctive changes to the 2012 IECC in regard to the thermal insulation requirements for low-slope roofs with the continuous insulation on the exterior side of the roof deck:

  • 1. It increased the minimum requirement of thermal R-value in each of the ASHRAE regions.
  • 2. It now requires that this minimum R-value be attained within 4 feet of the roof drain.

Item two is the game changer. If you consider that with tapered insulation you now need to meet the minimum near the drain, as opposed to an aver- age, the total insulation thickness can increase substantially.

PHOTO 2: Roof drains need to be secured to the roof deck with under-deck clamps so they cannot move.

PHOTO 2: Roof drains need to be secured to the roof deck with under-deck clamps so they cannot move.

THE ROOF DRAIN CHALLENGE

The challenge I see for designers is how to properly achieve a roof system design that will accommodate the new insulation thicknesses (without holding the drain off the roof deck, which I believe is below the designer’s standard of care), transition the roof membrane into the drain and coordinate with the related disciplines.

For the purpose of this tutorial, let’s make the following assumptions:

  • Steel roof deck, level, no slope
  • Internal roof drains
  • Vapor/air retarder required, placed on sheathing
  • Base layer and tapered insulation will be required
  • Cover board
  • Fully adhered 60-mil EPDM
  • ASHRAE Zone 5: Chicago area

FIGURE 1: Your detail should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck.

FIGURE 1: Your detail should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck.

Once the roof drain locations have been selected (for those new to this, the roof system designer should select the roof drain locations to best suit the tapered insulation layout), one should try to locate the roof drain in linear alignment to reduce tapered insulation offsets. The drain outlets should be of good size, 4-inch minimum, even if the plumbing engineer says they can be smaller. Don’t place them hundreds of feet apart. Once the roof drain location is selected, inform the plumbing and structural engineers.

STRUCTURAL ENGINEER COORDINATION
The first order of business would be to give the structural engineer a call and tell him the plumbing engineer will specify the roof drain sump pan and that the structural engineer should not specify an archaic, out-of-date sump pan for built-up roofs incorporating minimal insulation.

When located in the field of the roof, the roof drains should be at structural mid spans, not at columns. When a structural roof slope is used and sloped to an exterior roof edge, the roof drains should be located as close to walls as possible. Do not locate drains sever- al or more feet off the roof edge; it is just too difficult to back slope to them. Inform the structural engineer that the steel angles used to frame the opening need to be coped to the structure, not laid atop the structure. There’s no need to raise the roof deck right where all the water is to drain.

FIGURE 2: A threaded roof drain extension is required to make up the distance from deck up to the top of the insulation and must be screwed to a proper location (top of the insulation is recommended). To do so, the insulation below the drain will need to be slightly beveled. This is shown in the detail.

FIGURE 2: A threaded roof drain extension is required
to make up the distance from deck up to the top of the insulation and must be screwed to a proper location (top of the insulation is recommended). To do so, the insulation below the drain will need to be slightly beveled. This is shown in the detail.

PLUMBING COORDINATION
Now call the plumbing engineer and tell him you need a metal sump receiver (see Photo 1), underdeck clamp (see Photo 2), cast-iron roof drain with reversible collar, threaded extension ring capable of expanding upward 5 inches, and cast-iron roof drain clamping ring and dome.

Send the structural and plumbing engineer your schematic roof drain detail so they know exactly what you are thinking. Then suggest they place your detail on their drawings. Why? Because you cannot believe how much the plumbing roof-related details and architectural roof details often differ! Because details differ, the trade that works on the project first—plumbing— leaves the roofing contractor to deal with any inconsistencies.

Your detail at this point should show the steel roof deck, steel angle framing coped to the structure, the metal sump receiver (manufactured by the roof drain manufacturer), roof drain and underdeck clamp to hold the roof drain to the roof deck (see Figure 1).

PHOTOS AND ILLUSTRATIONS: HUTCHINSON DESIGN GROUP LLC

Pages: 1 2