Case Study Reveals Key Lessons in Roof Design

Photo 1. In order to manufacture materials inside the facility, humidity had to be added to the space in the form of hanging moisture dispensaries. This increased the relative humidity to 90 percent with interior temperatures reaching 90 degrees. Images: Hutchinson Design Group Ltd.

The client said, “The roof leaks in the dead of winter.” Interesting when the exterior ambient temperature is below zero. The client’s firm had purchased the metal building several years earlier and water had come in every winter. A key piece of evidence was that the original building was used for storage. The new entity purchased the building for manufacturing. Not just manufacturing, but manufacturing of medical-grade textiles that require the use of humidity to reduce static electricity. Not just humidity, but 90 percent relative humidity (RH), where visible water is sprayed into the air. (See Photo 1.) Interior temperatures routinely reached 90 degrees. Now, let’s see: 90 degrees with 90 percent RH inside, zero degrees outside, and 6 inches of vinyl face batt insulation compressed at the purlins with aged, open lap seams. Not good. The mission, if I chose to accept it, was to eliminate the leaking on a roof that was watertight.

Proposed Solutions

During my first meeting with the client, I was provided with proposals from roofing contractors and, sad to say, several roof consultants. Proposed solutions ranged from coating the metal, to flute filler and cover board with a mechanically attached thermoplastic membrane, to flute filler, 2 inches of insulation and adhered thermoplastic. None of the proposals identified the interior’s relative humidity and heat as a concern, and thus these issues were not addressed. So, a good part of the morning was spent educating the client as to why none of the proposed solutions would work. Imagine spending big bucks on a roof solution that would have only exacerbated that situation.

Photo 2. Rising humidity passed breaches in the vinyl vapor barrier in the insulation and condensed on the underside of the metal roof panels. The water would then drip down on to the insulation, and eventually the vapor retarder seams would open and water would pour in.

The existing building was a metal building by Kirby (similar to a Butler Building if that helps). The roof was a trapezoidal seam metal roof panel 24 inches wide on a low slope to an offset ridge. The panel runs from ridge to eave were 200 feet to the north and 100 feet to the south. The roof drained to a gutter on the north and lower metal roof on the south. The east and west roof edges were standard metal building rake metal. The walls were vertical metal siding with exposed screws. The roof and metal wall panels were set over vinyl faced insulation draped over purlins. While there was exhausting of the interior air — typically used in the summer — and some provisions for adding exterior air in the winter and summer, there was no overall mechanical control of the interior.

The Key Issue

While a freezer building has extreme energy low trying with every ounce of its being to pull hot humid air in, this structure has extreme energy high trying to “get out.” The warm, humid air is seeking every crack, split in the insulation facer, and open lap seam to move toward equalization. This warm, humid air was making its way to the underside of the metal roof panels, condensing, and running down the underside of the panel until it dropped off.

Figure 1. Typical Roof System Section

After time, the accumulation of the water in the batt insulation created a large belly until the adjacent lap seam broke and large amounts of water came cascading down. Soiled product had to be discarded. With rolls 5 feet wide and a 6 feet diameter, the losses could be substantial. Water on the floor was also a safety issue. Additionally, when this damage occurred the insulation layer now had an opening which sucked in even more interior air; the condensation increased and water dripping to the floor was an even bigger problem. This was occurring in numerous conditions, with the greatest accumulation of water in the insulation near the ridge. (See Photo 2.)

Determining the Solution

Prior to delving into a potential solution, a parti, or overall concept of architectural design, had to be developed. In this case I decided that the metal roof would become the vapor retarder for the new roof. Simple enough. If the metal roof is to become the new vapor retarder, the key was to keep it warm enough so that even if it came in contact with the interior air, it would not result in condensation. We did this by determining the dew point for several insulation scenarios and found that with the batt insulation still in place and 90 percent RH with a temperature of 90 degrees inside, with an exterior design temperature of minus 10 degrees, 6 inches of insulation above the 2.5-inch flute filler was required.

Photo 3. For budget reasons, the liquid flashing seal of the trapezoidal seams was eliminated. As the metal roof had to act as the vapor retarder, a self-adhered membrane was installed first over the trapezoidal seam and fit into the articulated seam with “finger” rollers, and then placed over the center of the panels and fit around the panel striations.

All roof system designs need to be thought of holistically, as the success depends on the sum of all the components working together. So, let’s start with the roof panel and structural system. Designers of metal buildings are notorious for minimizing each and every structural member to lower costs. A structural check found that the existing structure was able to handle the weight of a new roof system. Prior to proceeding, a mechanical fastener pull-out test was performed by Pro-Fastening Systems of Buffalo Grove, Illinois, an Olympic Distributor (need a special or standard anchor, these guys have it). The tests showed that the 22-gauge metal panel was able to engage the buttress thread screw.

To be effective, a vapor retarder needs to be airtight — or for you purists, have extremely low or no permeability at all — and this metal roof had to function as a vapor retarder. The steel roof panel itself is impermeable, but the seams, though mechanically locked, have the potential under interior pressure to allow air to pass through. The seams had to be sealed. The mechanical fasteners penetrating the metal roof panel needed to be sealed as well. The roof transitions at the vertical rake walls, gutter and low roof also needed to be sealed. After looking at the standing seams, it was decided that they could not be assumed to be airtight, so we selected to seal them with a liquid flashing. As the mechanical fasteners would penetrate the panel, a bituminous self-adhering and hopefully self-sealing vapor retarder was placed on the panel. (See Figure 1 and Photo 3.) Transverse laps, removing the ridge cap and infilling the opening were all addressed. The rakes presented unique challenges which took some good thinking on how to seal. Ultimately, it was decided that a combination of removing the rake metal and installing a prefabricated roof curb and membrane vapor retarder would do the trick. (See Figure 2.)

Figure 2. Rake Edge Detail

My initial thought was to begin the thermal layer with a layer of expanded polystyrene (EPS) on the deck designed to fit the trapezoidal seam profile. This left a void at the seams, so the void between the seam and EPS was sealed with spray foam insulation. (See Photo 4.) The insulation was then mechanically fastened. The thickness of the EPS was 3/8 of an inch greater in height than the standing seam to compensate for varying seam heights. Over the EPS, one layer of 2.6-inch fiberglass-coated faced, 25 psi polyisocyanurate insulation was designed to be mechanically fastened to the roof panel. The top layer of insulation was a 2.6-inch fiberglass-coated faced, 25 psi polyisocyanurate insulation, which was designed to be set in full spatter cover flexible polyurethane foam adhesive. A cover board with the receiver facer to which the membrane would be attached was designed to be set in a full coverage of splatter applied polyurethane insulation. (See Photo 5.)

Photo 4. The EPS was cut to fit the panel profile. The joint at the seam was sealed with spray foam insulation.

As the installation was to take place in late fall and during the winter, adhesive use was determined to be challenging if not impossible, so the roof cover selected was a 90-mil Carlisle FleeceBACK black EPDM. The fleece on the membrane would engage with a unique hook and loop facer and reduced by 95 percent the amount of adhesive required. (See Photo 6.) Six-inch seam taped end lap seams with self-adhering cover strips were designed, while the butt seams were also double sealed with 6-inch and 12-inch cover strips.

The rake edge was designed to be sealed at the top of the metal panels and raised with an insulated metal curb. (See Photos 7 and 8.) The wall panels’ reverse batten seams and bowed inward panel were designed to be sealed with a foam closure set in sealant. The architectural sheet metal on the rakes was a four-piece system of fascia and coping. The roof edge gutter was enlarged and reinforced to hold up to solid ice.

Construction

Photo 5. Once the EPS “flute filler” was in place, two layers of 2.6-inch coated fiberglass insulation were mechanically fastened into the standing seam panels. The high-density cover board was then installed in spray foam adhesive.

The project was bid out and AR Commercial of Aurora, Illinois, was selected. Work on the project began in October 2018 and was completed in April 2019. (See Photo 9.) Like any project, various miscellaneous items not anticipated arose, such as extreme cold early in the fall that precipitated the decision to mechanically attach the insulation in lieu of cold adhesive application. I also forgot about the residual water in the existing batt insulation. While we designed for 90 percent RH and temperatures of 90 degrees, we didn’t anticipate the 100 percent RH condition where the soaked batt insulation was located, which resulted in condensation occurring during the deep freeze. You’re never too old to learn something new. The batts were cut open, dried and all is good.

Sometimes you need a good roof over your head to keep you dry, even when it doesn’t rain.

Photo 6. The FleeceBACK 90-mil EPDM sheets were aligned, rolled out, broomed in and rolled.
Photo 7. Following the removal of the existing rake metal, the roof vapor retarder was extended down and over the existing construction and onto the metal roof panel. The contractor came up with an innovative two-piece roof edge curb that allowed for ease of installation.
Photo 8. Following the installation of the interior curb side, which was accomplished with a jig for continuous alignment, the curb was insulated and the exterior cap piece installed.
Photo 9. The finished roof prevented condensation from occurring even when the ambient temperature dropped to minus 28 degrees with wind chills near minus 50 degrees.

About the author: Thomas W. Hutchinson, AIA, FRCI, RRC, CRP, CSI, is a principal of Hutchinson Design Group Ltd. in Barrington, Illinois. For more information, visit www.hutchinsondesigngroup.com.

Regular Roof Inspections Help ‘Keep the Door Open’

A roof inspector makes field observations. Photo: Kemper System America Inc.

Regular roof inspections give consultants and contractors a chance to maintain relationships with building owners and managers and create value beyond any immediate repairs.

Commercial roofs should be inspected at least twice a year, typically in the spring and fall. Roof inspections are also advised after major weather events, though contractors may already be deluged with repair requests. Of course, building managers will be more receptive to discussing regular inspections during such times, even though time is short. A service flyer and readily available letter-of-agreement can help quickly close the deal, and be used after any major job throughout the year to create recurring business. Customers should clearly understand the service offer and any special provisions for emergency repairs or exceptions such as during wider emergencies.

Common Sources of Roof Leaks

  • Cracks in or around flashings and penetrations
  • Breaks in and around gutterways and drains
  • Poor drainage or debris-clogged drainage systems
  • Storm damage, tree branches, ice dams, etc.
  • Incidental damage by other trades during construction or maintenance
  • Excessive foot traffic at rooftop access points and around HVAC units and other rooftop infrastructure
  • Old or deteriorating roofing materials

While roof leaks can be caused in several ways, many common sources of leaks can be prevented with liquid-applied coating and membrane systems that fully adhere to substrates and are both self-terminating and self-flashing. Membrane systems are fully reinforced and create a seamless surface. High-quality systems are designed to withstand ponding water, ice, snow, UV light, as well as most chemicals. Unreinforced roof coatings can be used for repairs or complete restoration of the roof surface.

If only a small area is damaged, a limited repair is best, and usually possible with compatible materials over an existing system in good condition.Check if a warranty is in place, and if possible contact the manufacturer before the repair. Perform any repairs within the guidelines of the warranty.

For wider areas, a roof recovery is often possible right over the existing roofing. If interior leaks from a field area are evident, core samples can verify the condition of the existing roof assembly down to the deck. Built-up roofs (BUR), in particular, are susceptible to sun and temperature cycling. Tiny spider cracks and micropores can develop in the surface, and the layers below can absorb moisture and deteriorate. Water always travels to its lowest point and, if left unchecked, will damage the underlying structure.

On low-slope roofs, areas of ponding water are a prime target for inspections. If the roof is covered by aggregate or overburden, it must be cleared from around the lowest point of any low-lying areas, and other areas of suspected damage. A visual inspection can locate the source of an active leak, but there may be more than one source or a larger issue that may not always be visible. Broader sampling is needed to evaluate the general condition of the roof and the scope of any deterioration.

Quality workmanship and materials help avoid callbacks and ensure long-term relationships. After completing any necessary repairs, a PMMA, polyurethane or elastomeric membrane or coatings system can be installed to extend the service life of an existing roof. Elastomeric-based coatings are generally the best value for straightforward repairs and can be ideal for recovering metal roofs. Roof restoration, in general, can enhance building performance with “Cool Roof” products, especially those with a high solar reflectance index (SRI).

At the end of the day, an ounce of prevention and a prompt response to issues can help building owners avoid expensive headaches. People remember expert advice and quality service, especially in times of need. They also may tell others — which is another way regular inspections can help keep the door open to recurring business.

Pipe Flashing Seals in Extreme Environments

316L Stainless Steel Ultimate Pipe Flashing combats the effects of salt water, chloride, extreme sunlight exposure and pipe thermal movement.

316L Stainless Steel Ultimate Pipe Flashing combats the effects of salt water, chloride, extreme sunlight exposure and pipe thermal movement.

Lifetime Tool & Building Products has released its 316L Stainless Steel Ultimate Pipe Flashing, which combats the effects of salt water, chloride, extreme sunlight exposure and pipe thermal movement, the major causes of plumbing pipe flashing failures resulting in roof leaks. Made of true marine-grade stainless steel, the product provides a precision seal to the pipe with a flexible bushing made from an ultra-pure silicone elastomer, which accommodates daily movement from thermal changes on the roof. The pipe seal is reinforced with a solid PVC collar engineered to provide lifelong compression of the seal to the pipe.

Silicone Roof Patch Repairs Roof Leaks With One-Step Application

GacoPatch creates a seal within 30 minutes of application.

GacoPatch creates a seal within 30 minutes of application.

Gaco Western has developed GacoPatch, a fiber reinforced silicone roof patch designed for repairing roof leaks in a one-step application. Primers, seam tapes and top coats are not required.

A waterproof seal is created within 30 minutes of applying GacoPatch, protecting roofs from leaks. GacoPatch is suitable as a standalone roof patch and will not degrade under UV, temperature extremes or ponded water. The 2.5-gallon wide top pail makes GacoPatch application easy to do with a trowel or a brush.
 
GacoPatch comes with a 25-year limited material warranty.
 
GacoPatch is available through your local Gaco dealer. MSRP is $98.97. Visit here to find product locally.

Silicone Roof Coating Fixes Roof Leaks

Gaco Western's GacoElastomeric Silicone Roof Coating

Gaco Western’s GacoElastomeric Silicone Roof Coating

Gaco Western‘s GacoElastomeric Silicone Roof Coating offers customers a better choice for fixing roof leaks. Because acrylic elastomerics have issues with ponded water and UV degradation, they do not provide a lasting solution.

Not only does GacoElastomeric withstand ponded water, it remains flexible over time whereas acrylics become hard and brittle. It has higher solids than acrylics so more coating stays on the roof to provide better coverage and because of the unique chemistry it can be rained on after just two hours and won’t wash off the roof.

Forty Years of Roof Leaks Solved with Standing-seam Copper

Because the show must go on, what served as a canopy-style roof at the Miller Outdoor Theater, Houston, needed repairs in short order. Byrne Metals, Humble, Texas, installed more than 18,000 square feet of copper 238T standing-seam panels during the five-month off season by calling in the rollformer from McElroy Metal that runs panels right onto the roof deck.

Improvements included replacements of the east and west wings, a new soffit for the main sloped roof and the new 20-ounce copper standing-seam roof.

Improvements included replacements of the east and west wings, a new soffit for the main sloped roof and the new 20-ounce copper standing-seam roof.

“Everyone else who had tried to fix the problems focused on trying not to change the appearance,” says Karl Schaack, P.E., president of Price Consulting, Houston. “We realized providing a leak-free solution required some change in the appearance. We got a little pushback at first, but when we explained our design, they were just happy to know it wasn’t going to leak anymore.”

“It was a very challenging job,” says Neil Byrne, president of Byrne Metals. “This is an iconic structure in Houston, originally built in 1968. At the time, it won several awards for its design.”

Unfortunately, right from the start, the design didn’t hold up against the Texas rains. For more than 40 years, anyone who was hired to fix the problem, failed.

Schaack chose 238T symmetrical panels from McElroy Metal for the project. “It’s rigid and it meets high-wind requirements,” he says. “The 238T is symmetrical so if a panel gets damaged, you only have to replace one panel.”

BEFORE: The multi-million dollar renovation in Hermann Park served to correct canopy deficiencies that caused leaks above the stage and audience.

BEFORE: The multi-million dollar renovation in Hermann Park served to correct canopy deficiencies that caused leaks above the stage and audience.

The multi-million dollar renovation in Hermann Park served to correct canopy deficiencies that caused leaks above the stage as well as the audience, putting a real damper on the theater’s cultural and educational event offerings.

Byrne Metals went to work as soon as the 2013 season concluded in early November. Improvements included replacements of the east and west wings, a new soffit for the main sloped roof and the new 20-ounce copper standing-seam roof. The profile was McElroy Metal’s 238T symmetrical standing-seam panel. “Using copper helped the new roof blend in with the original framework,” Schaack says. “Especially as it ages, it will look great, like it’s been there all along.”

Changes in design to the updated roof, as well as a watertight standing seam installation, will help prevent future leaks.

Using copper helped the new roof blend in with the original framework. The profile was McElroy Metal’s 238T symmetrical standing-seam panel.

Using copper helped the new roof blend in with the original framework. The profile was McElroy Metal’s 238T symmetrical standing-seam panel.

The roof area between the existing Corten superstructure was framed with purlins, a metal deck was installed on top of the purlins, then a 1 1/2-inch nail base was installed over the deck along with ice and water shield. A giant reverse-slope diverter was built at the intersection, where the sloping roof connected to the stage wall. Valleys were lowered below the roof plane and there was a slight change in pitch that was overcome by rounding the insulation/plywood over the pitch change.

McElroy Metal’s job-site production equipment simplified the process of installation and made the job site safer. The rollformer was hoisted to the eaves on a scissor lift where panels were conveniently run onto the roof. Not only did this method eliminate the need for an expensive crane to get panels on the roof, it was safer as some of the panels were up to 110-feet long. Because of the unique shape of the roof, panels were cut to fit on the roof.

“We specialize in the unique and difficult,” Byrne says. “This is the kind of job we like. We generally have about 20 to 30 projects under contract at any one time, but this one required a lot of personal attention from our upper management, myself included. We had as many as 30 crew members onsite, working 10-hour days and some weekends, when necessary.”

A rollformer was hoisted to the eaves on a scissor lift where panels were conveniently run onto the roof.

A rollformer was hoisted to the eaves on a scissor lift where panels were conveniently run onto the roof.

As with all Byrne Metals jobs, safety was a major consideration during the evaluation and installation. “There are three things we consider important to staying in business,” Byrne says. “Safety, quality and productivity. We have a fulltime safety person on staff making sure we’re working safely on all jobs. This job required us to take into consideration some other factors like guys working long days, getting fatigued and the speed at which we had to work to complete the job on time. We enjoy a good challenge and Miller Outdoor Theater falls into that category.”

PHOTOS: McElroy Metal

Repair Roof Leaks in One Step

SmartFlash EZ Patch from CertainTeed Corp.

SmartFlash EZ Patch from CertainTeed Corp.

SmartFlash EZ Patch from CertainTeed Corp. is a single-component, high-performance, self-terminating cold-liquid-applied membrane that quickly patches leaks and cracks on flat and sloping surfaces. The UV-stable, pre-saturated self-adhering product is fleece-reinforced and made of one part urethane. Each package contains latex gloves and a pre-saturated fleece patch, measuring approximately 16 by 10 1/2 inches. It can be used on bitumen, single-ply membranes, concrete, wood and metal roofing surfaces. Once finished, there is no leftover material to clean up, and the roof is rainproof in one hour and completely cured in 48 hours.

Unmanned Aerial Vehicles Locate Roof Leaks

Tremco Roofing and Building Maintenance</a> proudly introduces SkyBEAM (Building Envelope Asset Mapping) for use throughout Canada.

Tremco Roofing and Building Maintenance introduces SkyBEAM (Building Envelope Asset Mapping) for use throughout Canada.

Tremco Roofing and Building Maintenance proudly introduces SkyBEAM (Building Envelope Asset Mapping) for use throughout Canada. SkyBEAM is a groundbreaking program that uses unmanned aerial vehicles (UAVs) equipped with high-resolution thermographic (infrared) and video cameras to help Tremco Roofing’s customers locate where their facilities may be leaking energy through gaps in the roof, facade or elsewhere, or may have wet insulation; and to find and photograph other potential problems on the building.

SkyBEAM’s thermographic camera graphically depicts energy inefficiencies by showing temperature variations within the building, a result of problems that can lead to increased operating costs, occupant discomfort and other issues. Poor or missing sealing around windows, for example, typically allows energy to escape. On rooftops, wet insulation retains heat longer than dry insulation; wet insulation can cause enormous long-term damage if not removed.

Instead of standing on the ground and trying to map the facade of a multi-story building by holding a thermal or video camera, or by sending someone up in a lift, the UAV flies to the precise height, does the mapping and returns. Buildings can be mapped without the expense of tools, such as scaffolding. SkyBEAM also eliminates the need to send technicians onto rooftops to conduct infrared scans, which means no safety risks.

SkyBEAM is available to Tremco Roofing’s customers anywhere in Canada through a relationship with Toronto-based Industrial SkyWorks, experts in aerial mapping and reporting.

View a video explaining the SkyBEAM system and its many benefits.