Understanding Is the Key to Preventing Trouble Spots With Masonry Chimneys

Restoration work in progress on a historic building shows copper chimney flashing being installed on a recently repaired chimney. Photos: John Crookston

There are almost as many types of chimneys as there are cars, but for this article, I am talking about masonry chimneys, and specifically masonry chimneys protruding through a steep-slope roof. These can take the shape of a simple chimney block unit with a clay flue liner running from the foundation thorough the roof, all the way to massive stone or brick structures with two and three fireplaces built in at different levels of the house. Chimneys can serve as load bearing structures and heating systems for the house. I have worked in homes where the chimneys are constructed so that the hot gas passes up and down through the structure of the chimney to heat the masonry mass before they escape out the chimney top, allowing this heated mass to radiate the heat for hours inside the house to supplement the regular heating system.

Eventually however, the chimney has to pass through the roof and into Mother Nature’s realm, and we as roofers have to deal with keeping rain and snow from working back into the building. Most of this task is accomplished with the flashing system at the roof level, but we need to remember that water and ice can also work through the mass of the chimney itself and cause leakage inside the structure. That is the reason for specifically mentioning masonry chimneys in the title above; when one is dealing with chimneys and water, moisture can be coming from all different angles, and all of these areas need to be addressed.

As part of the repair process, a drip line was cut into the underside of the chimney cap to prevent water from migrating across the surface.

I distinctly remember being at a local supply house years ago when a roofer ordered “a five-gallon bucket of flashing.” At best, plastic roofing cement is a temporary fix or patch, and eventually it has to come off. In my long career working on roofs, I have worked on thousands of shingle roofs and many hundreds of metal, tile and slate ones, too. I didn’t know whether I laughed or cried when the guy said that, but I did want to scream, “Flashing doesn’t come in a bucket!”

Masonry walls and chimneys bear on their own foundations and they move at different rates than the rest of the building. You have to allow for that movement, and you need to channel the water in the direction you want so that it is easier for it to flow off the roof rather than into it. Permanent flashing allows for the movement with hundreds of places where the metal can move while always at the same time directing the water lower on the plane of the roof and toward the bottom edge. Whatever the type of roofing material used (shingles, tile, slate, metal, thatch, etc.) and whatever type of flashing metal you use, the flashing always has to be lapped so that the water flows in the direction of the overlap. Depending on the slope, the lap has to be sufficient to allow for the worst possible amount of water flow you will encounter. The flatter the pitch, the more overlap you need. At less than 2/12 pitch, we start to deal with “flat roofing,” and that has its own challenges, though the principles are the same.

New copper chimney flashings were installed as part of this tile roof replacement project.

I could write about a detailed method to flash a chimney, but on every bundle of shingles sold, there are very good details printed and I would dare to say that not one in a million are ever read or even looked at. In this article, I want to explain the reasons why the details specify what they do. In the preceding paragraph, I mentioned that you have to make it easier for the water to flow off the roof rather than into it. That, in essence, is the principle of all flashing — and roofing, for that matter. If you fight the water flow, you will lose 100 percent of the time. Examples of “fighting the water flow” would be for instance lapping the flashings in the wrong direction, or perhaps building a saddle on the backside of a chimney and not extending it far enough sideways so that the water was trapped in the bottom corners. It could also be something as simple as cutting the shingles or slates too tightly against the flashings. As a general rule, always leave about a 3/8-inch gap between the vertical bend of the flashing and the cut of the shingle. This will allow the water to clean out the debris while keeping the joint water tight. Also, don’t jam the counterflashing tight against the horizontal surface of the flashings. This will also restrict the water flow and could cause leakage.

As an interesting aside, one very common mistake I see with cutting valleys is for roofers to not trim back the top corner of a shingle in the valley as shown on all of the packages. The water will catch on that top corner if it is not cut back and track along the top of the shingle until it finds a way into the envelope of the roof. This applies to all valleys, but in this instance, I am specifically speaking of the valleys created when a saddle or cricket is installed behind a chimney. It is also important to not cut the valley shingles in the center of the valley or the low point. Keep the cut line about an inch out of the center of the valley so that the water can again do your work for you by cleaning out the debris. This will also keep the water away from the top corner of the valley shingle.

Problems With Chimneys

Inspecting and repairing any damage to an existing chimney is an essential part of steep-slope re-roofing projects. Loose mortar, cracks in the bricks themselves and spalled surfaces are obvious signs of water damage.

Proper flashing application is crucial, but many of the problems associated with chimney leakage have to do with the chimney itself. Until the advent of the high-efficiency furnaces, most exhaust gasses from the heating of the building went up the flue of the chimney. When more efficient furnaces were introduced, they reduced this gas and excess wasted heat, yet many were vented into the same flue. By definition, a 50 percent efficient furnace puts half of the energy and heat up the flue, while an 80 percent unit would only vent 20 percent of the heat into the same volume, heating the house with the other 80 percent. It takes heat to create the draft necessary to carry moisture out of the chimney. Any gas will cool when it expands, and we are drastically cutting the amount of heat when installing a more efficient furnace. If we don’t reduce the size of the flue, the water vapor can condense back into water before it escapes from the top of the chimney. Mostly, this occurs in the section of chimney directly exposed to the weather, which would be the part sticking out above the roof line. It was common years ago to see the face of a lot of the bricks spalled or breaking off from the rest of the brick. This was caused by the water vapor condensing and then saturating the brick, freezing, expanding and breaking off the surface. If you still have one of the 80 percent units, it is important that you have a smaller flexible metal flue liner installed to reduce the volume and increase the speed with which the gasses escape. This in normally not a problem anymore, as most units now are 95 percent efficient and are vented out the side of the building using a plastic pipe.

This granite chimney shows signs of damage caused by water migrating underneath the chimney cap.

Very few of the homes built today even have a masonry fireplace or chimney, mostly because of the type of furnace used and modern codes. Most fireplaces installed today are zero-clearance units and are basically a gas appliance similar to a gas stove. Many of the older homes that still have wood burning fireplaces have switched them to a gas burning unit, and this will cause the same problem as switching the older furnaces if a smaller sleeve is not installed to reduce the volume of the flue. The biggest problem with this switch is that the effects are not immediately apparent, but delayed, often by several years. We worked on a large condominium project in the early 70s that had dozens of large chimneys, most with several fireplaces on different levels. At some time in the 90s, they all had gas inserts installed, without changing the size of the flue liners. Not all of the chimneys had problems; only the ones that used the gas logs. No matter how often they redid the bricks on the tops of the chimneys, they kept on breaking and spalling. The flaws in the brick and cracks in the caps caused by the water vapor freezing and expanding also caused regular leakage in the chimneys by loosening the counter flashings and letting water past the step flashings and head wall flashings. The caveat to be learned here is that there is a cause and effect that occurs for every action taken, and before making a change it is important to do some research and determine what the effects will be and what has to be done to make sure that it doesn’t do more harm than good. When roofing an existing structure, it’s also important to determine what other changes have been made to the structure in the past.

Erecting proper scaffolding is often the essential first step in the chimney repair process.

Current building codes and modern engineering make the new homes built more efficient and less prone to these types of problems; however, there are millions of older homes out there that need to be retrofitted or in some case “re-fixed” or “unfixed” to make them work.

The one big advantage we are working with today is that there are very few “roof overs” done on steep-slope roofs, as most districts require that the old roof be removed before a new one is installed. This will allow for all of the flashings to be replaced. If chimneys still exist but are no longer used, the possibility might exist for them to be taken down, having the framing replaced and the opening covered and roofed. If this is done, make sure that you take the chimney down to the height of the ceiling joists, cap it at that point and insulate above it.

When re-roofing an existing structure, it’s important to inspect the roof system for damage and determine if any changes have been made to the structure in the past.

If the chimney is left in place, it is important to have the masonry mass inspected and fixed before the roof is done to avoid damaging the new roof. Install a new flashing/counter-flashing system, and make sure to follow the directions printed on the shingle wrappers. My objective here is not to reinvent the wheel, but to make sense of what they are telling us to do. Many years ago, there was a commercial with a tag line that went “It’s not nice to fool Mother Nature.” The truth is that you can’t. If you work with gravity and nature, on the other hand, you can eliminate a lot of the problems we are fighting with on the roofs and in this business. The choice is yours.

This architectural detail from The NRCA Roofing Manual: Steep-slope Roof Systems—2017 shows the proper method for flashing a masonry chimney. Detail courtesy of the National Roofing Contractors Association (NRCA).
The packaging for shingles often contains product-specific details for flashing chimneys and valleys, such as this diagram for CertainTeed’s Carriage House shingles from the CertainTeed Shingle Applicators Manual, 14th edition. Detail courtesy of CertainTeed.

About the Author: John R. Crookston is a roofing contractor and consultant located in Kalamazoo, Michigan. He has more than 60 years of experience in the roofing industry and has written technical articles for a variety of publications under the pseudonym “Old School.”

Understanding EPS Flute-Fill Insulation, a Tailor-Made Solution for Re-Cover Projects

One board of flute-fill expanded polystyrene insulation fits snugly between a metal roof’s flutes. Photos: Insulfoam

With a typical service life of 20-plus years, metal roofs continue to grow in popularity for their longevity and reduced lifecycle costs. While metal does inarguably outlive traditional roofing materials like asphalt, roofers know all too well that nothing truly stands the test of time. So, when a metal roof’s reign eventually comes to an end, savvy contractors are ready with re-cover tools if the existing system is serviceable as a substrate.

In an industry continually constrained by a lack of qualified workers, roof re-covers crucially save on time and labor. By not tearing down the entire assembly and starting from scratch, re-covers help cut down on the number of workers needed to remove the existing membrane, fix any deterioration to the underlying structural deck and install the new system. This is beneficial from more than the standpoint of the skilled trade shortage.

Metal re-covers further provide an opportunity for construction crews to add additional insulation to the roof. This step can improve a metal roof’s efficiency by bolstering thermal performance and improving moisture management. But which insulation can best save on material and labor costs in metal re-covers, while still providing a well-insulated roof assembly? One practical solution is flute-fill expanded polystyrene (EPS) insulation.

Why Flute-Fill EPS Insulation?

Lightweight flute-fill insulation consists of closed-cell EPS. Manufacturers can engineer the product to meet or exceed the requirements of ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. It can be factory-taper-cut, square-cut or profile-cut to satisfy project needs, while meeting a range of compressive strengths. This flexibility allows flute-fill EPS insulation to function as a tailor-made solution for use over structural standing seam metal roof systems.

By eliminating the spaces between the seams, flute-fill expanded polystyrene provides an even foundation for roofers to install additional layers.

The insulation’s ease of customization is a key benefit, as standing seams (or “flutes” as they are commonly known) can prove problematic during metal roof re-cover projects. Specifically, the raised, interlocking seams add a level of complexity for crews to work around and establish a uniformly smooth surface for the new membrane system.

To overcome this challenge, crews traditionally had to cut insulation and place many individual pieces to fill flutes. Flute-fill EPS insulation is an easier alternative since it can be custom-cut to fit exactly between the standing seams. By eliminating the spaces between the seams, roofing teams are left with a stable, even foundation ideal for laying multiple roof layers and blocking heat transfer. And by filling in the channels, contractors do not need to worry about their insulation’s ability to span the raised seams without failing.

More importantly, flute-fill EPS insulation also cuts down time, material and labor costs. With flute-fill EPS insulation, workers no longer have to cut panels to fit between metal flutes, freeing up time to complete other tasks. Simplifying the jobsite, roofers only need to lay one layer of this dense material between the seams with another cover board on top, depending on specifications. Flute-fill insulation further minimizes the use of insulation above the flutes, thereby reducing the possible need to raise curbs and other rooftop systems. As for labor savings, less moving parts require fewer people to get the job done. Overall, some manufacturers estimate that flute-fill insulation saves up to 25 percent on costs compared with similar products.

The R-Value Advantage

Contractors know that metal naturally has a low insulating R-value, and so the rigid foam insulation they utilize must have a high, stable R-value. What is more, the 2015 International Energy Conservation Code and ASHRAE Standard 90.1 both have insulation prescriptive R-value requirements for metal building roofs. With its long-term thermal performance and water-resistant properties, EPS is a logical choice for bolstering these roofing systems.

Less insulation saves time, conserves resources and reduces labor on the roof.

While crews most commonly use polyiso rigid foam in roofing applications, the insulation may not deliver consistent thermal performance. Since the gas blowing agent used to create polyiso can leach out, replaced by air, high initial R-values can similarly decrease during the product’s time in service. For example, the EPS Industry Alliance estimates that polyiso’s R-values can degrade up to 30 percent over time.

In contrast, EPS is manufactured without using any blowing agents, retaining its R-value throughout its time in service. It is not uncommon to see EPS products like flute-fill with 20-year thermal performance warranties.

Listed R-values are certainly integral to project outcomes. However, building professionals know real-world moisture management also impacts thermal performance. When insulation is exposed to water, R-values drop, as the liquid displaces insulating air. In fact, high moisture volumes can cause rigid foam insulation products to lose up to half of their insulating R-value. It naturally follows then that the drier the rigid foam insulation, the higher the R-value.

Applied in the real world, third-party agency Energy Materials Testing Laboratories found that EPS did not absorb significant moisture when installed in well-built roofs. (See “Moisture Resistance” at www.epsindustry.org.) Even when exposed to cold and damp conditions for extended periods, the rigid foam insulation maintained between 95 percent and 97 percent of its thermal efficiency. Therefore, EPS’ non-hygroscopic properties make it an ideal candidate for metal roofs.

Insulation Solution Has Roofers Covered

Metal roofs continue to gain traction across residential and commercial applications, which translates to more metal roof re-cover projects on the horizon. EPS rigid foam insulation is one tool contractors can have in their tool belts during these re-covers, combating metal roof’s common challenges of sub-par insulating capabilities and improper installation, which can lead to leaks.

This illustration shows the various types of flute-fill expanded polystyrene taper cuts available.

Amidst the industry’s overwhelming concerns of finding quality residential and commercial workers, EPS flute-fill insulation simplifies the installation process, requiring fewer person-hours on the jobsite than other options. This efficiency and streamlined functionality will see roofers through turbulent times and economic booms alike.

About the author: David Stassi is field technical support manager for Insulfoam, a manufacturer of expanded polystyrene (EPS) insulation products. For more information, visit www.insulfoam.com.

The Top 5 Issues in Metal Roof Installation

Metal roofs offer a number of benefits for both homeowners and roofing contractors. Installation problems, however, can cause functional or aesthetic issues that can result in problems, delays and unhappy clients. Following are the five most common roof installation issues and how to solve them.

1. Metal Shavings Causing Rust Streaks

Installing a metal roof requires drilling through the aluminum or steel roof panels to attach them to the substrate. The process creates metal shavings, especially at rivet holes along the ridge cap or when drilling through multiple layers of roof panels.

These metal panels show evidence of rust stains caused by metal shavings. Photos: Gulf Coast Supply & Manufacturing

Those tiny shards of metal can cause rust and stains on the roof, as well as corrosion that shortens the lifespan of the roof. The more layers of metal a crew has to drill through, the more shavings will be produced.

“Shavings are no problem when removed quickly,” says Paul Hope, field service technician for Gulf Coast Supply. “It is when they are left behind that they become an issue.”

“When metal shavings sit on the roof for a week to a month they start to corrode,” Hope says. “That corrosion leads to staining of your panels, and that staining leads to unhappy homeowners.”

Roofers should get in the habit of either sweeping or blowing metal shavings off of the roof at the end of the workday, according to Hope.

2. Improperly Installed Underlayment

Underlayment has to be carefully measured and lapped to avoid moisture infiltration into the building envelope. Local building codes specify lap coverage guidelines and slip sheet placement for underlayment installation.

Underlayment must be carefully measured and installed correctly to prevent moisture infiltration. The underlayment shown here is not lapped correctly.

Underlayment is designed to act as a secondary water barrier in case rain makes it past the metal roof. Some of the most common causes of water intrusion are fastener failure, wind-driven rain in extreme storms, or metal-to-metal connections with no sealant.

Avoiding underlayment issues is easy to do if the crew follows installation instructions and code requirements. If underlayment is not installed correctly, however, replacement costs can be expensive and involve removing the metal roof, replacing the roof substrate and installing new underlayment.

3. Over-Tightened and Under-Tightened Fasteners

Proper fastener installation is critical to the efficiency of a roof system. Because fasteners penetrate the metal roof, underlayment and roof deck, they can allow for water infiltration into an otherwise waterproofed roof.

Over-tightened screws compress the washer too much and can cause water to pool. Under-tightened screws will not hold panels securely and can cause premature wear of fasteners and panels.

During the installation, screws must be straight and tight to perform as intended. Fasteners that are not installed straight do not form a proper seal. And even when they are straight, over-tightening the screw compresses the washer too much, forms “dimples” in the metal panel and causes water pooling that can then infiltrate the attic.

Under-tightened screws won’t hold the roof panel securely and can cause premature wear of both the fastener and panel.

4. Inadequate Onsite Storage Arrangements

Roofing materials should be delivered in a particular sequence, close to the time roofers will need them. The longer roofing materials, such as panels, are stored on site, the more prone they will be to damage from the elements or construction-site mishaps.

Improper storage of roofing panels at the jobsite can lead to damaged and corrosion.

Workers should pay attention to where and how materials are stored. Are they out of the way of vehicles? Are they on a flat surface? Are they elevated on one end to allow for drainage of rainwater?

Standing water, especially on unpainted panels, can cause wet storage stains or what is known as “white rust.” Sand, dirt and debris can also damage metal panels, causing permanent stains before they are ever installed on a roof.

5. Delays Due to Worker Injury

Safety is crucial on any jobsite but especially when installing a metal roof. Injury and accident prevention should be the primary duty of crew chiefs and workers alike. Accidents can not only send workers to the hospital, they can affect scheduling and job productivity as well.

“Medical bills, downtime, and loss of skilled laborers for extended periods of recovery can take place,” Hope says. “It is the responsibility of every individual to properly protect themselves from day to day.”

Proper safety equipment is essential. Gloves and Kevlar sleeves can help roofers protect themselves from cuts.

Falls are the most common potential metal roofing injury. Workers should use harnesses when on the roof and in any other fall-risk situations. Someone on the crew also needs to maintain the condition of the safety equipment. “Nicks in the harness can jeopardize your entire fall system,” Hope says.

Cuts caused by the sharp edges of the metal panels are also a hazard. Gloves and Kevlar cut sleeves can help roofers protect themselves.

Less common threats include electrocution and burns. Electricity, whether from a live current or lightning, can travel through the metal. Rubber shoes and gloves can protect roofers from potentially fatal shocks. Burns are less common, but in hot climates, the sun can heat metal enough to cause an injury. Workers can protect themselves with gloves and protective clothing.

Taking care to address these five common metal roofing installation issues can result in a smoother, more effective process, fewer problems and more satisfied clients.

About the author: Jared Pearce is the technical services manager at Gulf Coast Supply & Manufacturing. The son of a general contractor, Pearce has been around the construction industry his whole life. He is also a native Floridian and a Coast Guard veteran. Gulf Coast Supply has been a trusted choice for metal roof products throughout the Southeast for more than two decades. Through its Contractor’s Advantage program, Gulf Coast offers both classroom and hands-on seminars to help fill the industry’s need for qualified roofers. For more information, visit www.GulfCoastSupply.com.

Improve Commercial Roof Performance With Staggered Insulation Layers

Photo: Hunter Panels

Selecting the right components for a project can dramatically improve the performance and longevity of the overall building. In a commercial roofing project, the chosen insulation and the installation technique are critical to a building’s resilience and thermal efficiency.

From a physics standpoint, energy flows from a region of high to low potential (from warm to cold). Therefore, a significant amount of heat can leave a building through an inadequately insulated roof assembly during heating season (winter) and enter a building through an inadequately insulated roof assembly during cooling season (summer). A building with an under-insulated roof assembly may require more energy to compensate for these heat gains and losses.

The benefits of installing multiple, staggered layers of rigid board insulation have been well known for years. Industry authorities, including National Roofing Contractors Association (NRCA), Oak Ridge National Laboratory (ORNL), Canadian Roofing Contractor Association (CRCA) and International Institute of Building Enclosure Consultants (IIBEC), formerly RCI, Inc., have recognized these benefits; and contractors, designers and specifiers have followed the roofing industry’s long-standing recommendation for the installation of staggered insulation layers.

Using the optimal roof insulation product also will impact performance. Polyiso insulation offers key advantages in meeting stricter building standards and improving energy efficiency. Polyiso has a high design R-value compared to XPS, EPS, and mineral wool board. Lightweight and easy to trim, polyiso can be layered to reach the desired R-values without being cumbersome to install.

Why Are Multiple, Staggered Layers of Insulation Important?

In 2015, the International Energy Conservation Code (IECC) increased the R-value requirements for the opaque thermal envelope in many climate zones across the United States. As a practical matter, most roofs will require two or more layers of insulation to meet the local energy code requirements. In the 2018 version, the IECC was updated with specific installation requirements for continuous roof insulation. The 2018 IECC explicitly calls for continuous insulation board to be installed “in not less than 2 layers and the edge joints between each layer of insulation shall be staggered” (Section C402.2.1 Roof assembly). 

Figure 1. Multiple, staggered layers of insulation can minimize air infiltration and reduce or prevent condensation in the roof system.

Staggering the joints of continuous insulation layers offer a number of benefits:

· Increased thermal performance/reduced thermal loss: The staggered joints on multiple layers of insulation offset gaps where heat could flow between adjacent boards. The staggered approach to installing insulation reduces thermal bridging in the roof assembly. A fact sheet on roof insulation published by Johns Manville (RS-7386) notes that as much as 8 percent of the thermal efficiency of insulation can be lost through the joints and exposed fasteners of installations that use only a single layer of insulation.

· Air intrusion: When conditioned air enters the building envelope, often because of pressure gradients, it carries moisture into the roofing system. This moisture will undermine optimal performance. A peer-reviewed study on air intrusion impacts in seam-fastened mechanically attached roofing systems showed that air intrusion was minimized by nearly 60 percent when the insulation joints were staggered between multiple layers of insulation. (See “Air Intrusion Impacts in Seam-Fastened, Mechanically Attached Roofing Systems,” by By Suda Molleti, PEng; Bas Baskaran, PEng; and Pascal Beaulieu, www.iibec.org.)

Additionally, by limiting the flow of air and moisture through a roof system, staggered layers of insulation in a roof assembly can reduce and/or prevent condensation. The condensed moisture if allowed to remain and accumulate in the system can damage the substrate and potentially shorten the service life of a roof. A properly insulated roof can also prevent the onset of condensation by effectively managing the dew-point within the roof assembly. 

· Resilient roof assemblies: Staggered joints can reduce the stress put on a single insulation layer and distribute that stress more evenly over multiple, thinner insulation joints. For example, in an adhered roof system, the installation of multiple layers of insulation can minimize the potential for membrane splitting. In this system, the upper layer(s) of insulation can protect the membrane from potential physical damage caused by fasteners that are used to attach the bottom layer of insulation to the roof deck.

· Ponding water: Roof slope is often created through the use of tapered insulation systems. These systems offer an opportunity to stagger the joints by offsetting insulation layers and improve overall energy performance of a system. If the added insulation layer is tapered, the slope provided can improve drainage performance of the roof. Rainwater that does not drain and remains standing, collects dirt and debris that can damage or accelerate erosion of roof covering. Integrating tapered polyiso system with staggered joints into a roof’s design will not only improve the thermal performance but also can improve drainage and thus overall longevity of the system.

· Puncture resistance: Roof cover boards are commonly installed to provide a suitable substrate for membrane attachment as well as protect the roof assembly from puncture and foot traffic. When using products like polyiso high-density roof cover boards, the joints should also be staggered with the underlying roof insulation. This ensures the benefits discussed above are preserved in systems utilizing cover boards.

Installation Best Practices Are Keys For Success

A properly designed roof system that utilizes high-performance polyiso insulation products is a strong foundation (or cover) for energy-efficient and sustainable construction. However, the designed performance can only be achieved through proper installation. Implementing industry best practices such as the installation of multiple layers with staggered joints will optimize energy efficiency of the system and will help ensure that the roof system performs during its service life.  

To learn more about the benefits and uses of polyiso insulation,please visit the Polyisocyanurate Insulation Manufacturers Association website at www.polyiso.org.

About the author: Marcin Pazera, Ph.D., is the Technical Director for Polyisocyanurate Insulation Manufacturers Association (PIMA). He coordinates all technical-related activities at PIMA and serves as the primary technical liaison to organizations involved in the development of building standards. For more information, visit www.polyiso.org.

Developing Roof Systems That Prevent Energy Loss

A fully-adhered membrane will prevent fluttering and minimize energy loss. Photos: Hutchinson Design Group

Several millennia ago, early man — and the wife and kids — decided that life in a cave was a little dark, damp and confining, and started thinking about a better place to live. This led, eventually, to the need for a roof. Sod was the obvious first choice for a roofing material — abundant supply, close at hand, pretty simple to install, providing good insulation — but not very waterproof and very prone to catching fire in dry weather. Whether that caveman knew he had installed the first “green roof” is unknown.

Fast-forward to the multiple choices that we now have to shelter ourselves and the structures where we work, learn, shop and perform hundreds of other activities. In some ways, the challenges are the same as they were thousands of years ago: keep the occupants dry and comfortable and protect the systems in the building, although those systems are vastly more complex than they were for our ancestor emerging from his cave. A few other things have changed, as well, including the cost of energy for heating, cooling and running building systems. The challenge today is still to keep a building and its occupants protected from the outside elements. But an equally important challenge, given rising energy costs, is to keep energy expenses from literally going through the roof.

Insulation should be installed in multiple layers with the joints staggered.

Roofing contractors are meeting this challenge by paying increased attention to places in a roofing system that might allow penetration of air, either escaping from the inside or penetrating from the outside. To get an update on state-of-the art thinking, we talked to one of the most knowledge people who study this problem.

André Desjarlais is the Program Manager of the Building Envelopes Research Program at Oak Ridge National Laboratory. He has spent the majority of his professional career “developing novel building envelope technologies and assessing their market viability.” Much of his recent focus has been on developing systems that will prevent energy loss. Roof color has been extensively discussed related to energy use, with general agreement that reflective roofs save energy in warm to hot climates, and dark membranes are the most economical choice in cool to cold climates. However, there are a broad variety of other factors that influence the efficiency of a roofing system.

Proper installation of the insulation is key to meeting code requirements and preventing air leakage.

For instance, referring to low-slope roofing, Desjarlais points out that adequate insulation, defined by recent building codes, is essential to ensure an effective roofing system. “If we are in a jurisdiction that has adopted the most recent versions of the energy code, IECC 2015, we’ve really done a good job of increasing our insulation levels. Hooray for us — we have finally acknowledged that energy is important and we are mandating reasonable amounts of insulation to be put in commercial roofing.” Experts also note that it is important to install insulation in multiple layers and stagger the insulation joint. Studies have shown that up to 10 percent of the insulation’s R-Value is lost due to joints in the insulation.

Assuming the roof color is appropriate to the specific climate where it is being used, and insulation levels meet the latest codes, then other potential energy losses, specifically air flow or air leakage, become important. Desjarlais says the connection between the membrane and the perimeter of the building requires special attention. “How do we attach the membrane to the perimeter of the building and how do we make that connection continuous with the air barrier system of the walls?” Desjarlais says it is critical to avoid creating a path or paths for air to flow around the membrane and into the perimeter. “We need to have a continuous air barrier system, so the issue is how do you connect the wall and the roof system together?” He points out that this task can be most challenging during a retrofit to replace the roof since the parameters of the job may not include repair on the adjacent walls. Nonetheless, the connection still needs to be made securely.

The connection between the membrane and the perimeter of the building requires special attention. There should be no voids in the insulation at the perimeter.

It’s also important, Desjarlais continues, to note that there are several ways for air to either penetrate or escape from a building. “Air leakage” refers to air that starts on one side of the roof and gets to the other side, so it can start from the inside of the building and work its way outdoors, or start from the outside of the building and work its way in. Either way, there is energy loss.

Another kind of energy loss is “air intrusion.” This occurs when air that starts inside the building works its way through the roofing system but doesn’t make it to the outside, instead looping back to the interior. This is likely to be a problem when single-ply membranes are mechanically attached. When wind flows over the surface of the roof and the membrane billows slightly, it creates a void, and that void needs to be filled. The air that fills the void is coming from the interior of the building. So as the roof flutters, it is pumping air into and out of the roofing system. The air can also be carrying moisture that can condense under the roofing membrane.

If you are in a cold climate, the warm air from the interior of the building is chilled by its contact with the cold roofing membrane; if it is summer, the air becomes warmer. Either way, the air needs to be reconditioned when it returns to the interior of the building, driving up energy costs. [Click here, for a video showing the impact of “fluttering” on a roofing system, and the preferred alternative of a fully adhered system.

If fluttering is a potential problem, Desjarlais says, some kind of control should be put on the interior side of the roof, to make it hard for the air to flow to the underside of the membrane. This also extends the service life of the roof, preventing the wear and tear on the roofing membrane that can occur with fluttering.

There’s no doubt that creating an energy-efficient roofing system demands an investment in time and resources. But some currently available roofing membranes are setting new records for durability: EPDM, for instance, if properly maintained and installed, is projected to last up to 40 years. A well-designed, well-installed roofing system that prevents energy loss over four decades could provide invaluable protection against rising energy costs and a volatile energy market.

About the Author: Louisa Hart is the director of communications for the Washington-based EPDM Roofing Association (ERA). For more information, visit www.epdmroofs.org.

Safety Tips and Best Practices for Roofing in Frosty Temperatures

Installing a roof in cold weather is nothing to sneeze at. While roofing contractors in the deep South may not have to worry about business slowing down in the winter, the majority of contractors must contend with cold temperatures, snow, ice and sleet. And even when these extreme weather conditions allow work to be done, they can still create many product and safety issues on the job. 

No matter how well you’ve honed your craft, roofing in cold weather is a challenge for any seasoned contractor. In addition to thinking about the safety of your workers, you must also consider the usability of supplies and equipment, which may be susceptible to the elements. 

For instance, in lower temperatures, certain types of asphalt shingles can become less flexible and equipment may freeze. Also, you should ask yourself: Can I keep my workers motivated and focused on the quality I expect? When roofers are uncomfortable or can’t work safely, they begin to worry about themselves more than the work they’re doing — and justifiably so. 

Before proceeding with your next cold-weather roofing job, consider the following precautions and recommendations. 

Product Considerations

The first rule of cold-weather roofing is to follow all manufacturers’ cold-weather installation guidelines. Different manufacturers specify different minimum temperatures for their products. If the temperature is below that minimum, you will need to take extra precautions to ensure the roof shingles are handled correctly and the product seals properly. 

For example, while asphalt shingles have been successfully used in cold climates for more than a century, they become less flexible at temperatures below 40 degrees Fahrenheit. 

When asphalt shingles lose their pliability, they become prone to cracking and other problems, including failing to lie flat and not holding their shape, which can result in granule loss, humping and other damage. Lower temperatures will also keep the shingle sealant lines from achieving proper thermal activation. 

Because of the increased risk of shingle damage and the shingle not sealing correctly in cold temperatures, workers should keep the following things in mind:

  • Never throw or drop shingles. 
  • Give shingles time to warm up before installation if they have been stored in freezing temperatures. Cold shingles — especially fiberglass shingles — may crack on the back when nailed to the deck, which can cause roof leaks. Best practice: When installing shingles in low temperatures, nail them by hand to avoid the “blow through” that a high-powered nail gun can cause.

Remember that most sealants won’t thermally activate at temperatures below 40 degrees. Instead, seal strips must be hand sealed with an approved asphalt roofing cement or other manufacturer-approved adhesive. 

The Asphalt Roofing Manufacturers Association (ARMA) recommends that shingles be pressed into the asphalt cement so that the adhesive reaches almost to the shingle edges, but is not exposed. For laminated shingles, ARMA says at least three spots of sealant may be used. If not sealed properly, eaves and rakes can be extremely susceptible to wind blow-off. 

The association also suggests the use of open metal valleys in cold weather because installing closed and woven valleys require shingles to be bent, which could result in damage. 

To prevent ice dams — the frozen water that can build up at the eaves of a roof — be sure to install proper roof and attic ventilation in addition to a premium ice and water roof underlayment, which provides a second layer of protection in cold-weather conditions. Ice and water underlayment can be used along eaves, valleys, flashings, hips, ridges, dormers, rakes, skylights and chimneys. Properly ventilating a roof will help ensure maximum protection against ice dams.

Before installing roofing underlayment, be sure that the deck is completely dry so the moisture doesn’t cause wrinkling or buckling of the underlayment. This wrinkling can telegraph through the shingles, creating cosmetic and performance concerns. In addition, trapped moisture can contribute to shingle blistering. 

Overall, when roofing during cold-weather months, check the forecast and plan for potential delays. Better yet, try to work on bright, clear days, when the sun can bear some of the burden and help warm up the roof deck. 

Safety Concerns

Near-freezing temperatures not only create issues with supplies, they can also pose safety risks to workers.

To avoid frostbite, roofers should layer up in clothing such as ClimaWarm and Hyperwarm, which provide warmth, breathability and protection from wintery weather. Even with the proper attire, workers should beware of the signs and symptoms of frostbite, which include prickling skin, numbness and — worst of all — clumsiness caused by stiff joints and muscles. 

In addition to following the Occupational Safety and Health Administration’s (OSHA’s) safety regulations for harnesses and fall-protection systems, roofers should always wear shoes with good traction — but especially in cold weather, when surfaces can become slippery. 

Also, encourage everyone to take regular warm-up breaks throughout the day, limit work schedules during extreme weather conditions and consider investing in on-site heating equipment, such as portable foot warmers.

To best prepare yourself and your crew for winter jobs:

  • Plan work around the shorter daylight hours, as well as weather conditions that may prevent roofers from safely being able to put in the necessary hours. 
  • Expect work performance to slow down due to dexterity issues and other natural body-responsive reactions caused by cold temperatures. 
  • Anticipate the extra time that will be required to clear snow from roofs and protect the surface from the elements while work is being performed. 
  • Remember that even a thin layer of snow can camouflage skylights, other materials and debris, which could pose a tripping or falling hazard. 
  • Because working in cold weather takes just as much, if not more, physical exertion as working in warm weather, roofers should be sure to drink plenty of fluids to prevent dehydration. 

Ultimately, the best advice is to be prepared. Take a cold hard look at the weather forecast and plan accordingly, taking into consideration worker safety, product usability and equipment functionality. Being flexible and ready to adjust work as needed can keep winter business from freezing up altogether.

About the author: Paul Casseri is the product manager of the Roofing Shingles and Underlayment Division for Atlas Roofing Corporation. For more information, visit www.atlasroofing.com.

Expert Tips For Shingling A Cone-Shaped Roof

Cone-shaped roofs are one of those projects that contractors either love to do or avoid like the plague.

A prominent architectural feature on Queen Anne- and Norman-style homes, cone-shaped roofs are also found on Armenian and Georgian churches and medieval towers and castles. Their sloping and curved geometric surfaces can be difficult and labor intensive to shingle, especially for roofers who are accustomed to working only with straight lines.

Whereas a simple pitched roof typically has two or more sides and a hip roof has at least four sides, a conical or turret-style roof can appear to have an infinite number of sides. Some cone-shaped roofs have three to eight flat sides that create more of a geometric shape, such as a pyramid.

So, the challenge is: How do you install flat shingles on this intricate, rounded surface?

The underlayment should be applied vertically, perpendicular to the eave, as shown in this figure from the ARMA Technical Bulletin titled “How to Shingle a Cone Roof.” (Copyright Asphalt Roofing Manufacturers Association, reprinted with permission.)

Getting Started

Thanks to their flexibility, modern asphalt shingles can be installed on roofs of any shape.

To begin shingling a cone roof, you need to know three measurements: the length of the rafter, the diameter of the cone and the widest piece of shingle you’ll be using.

To determine the distance around the base of the cone, multiply its diameter by 3.14. For example, if the diameter is 20 feet, the perimeter would equal 62.8 feet. With a 12-inch-wide shingle, you would need 63 shingles in each row around the cone.

Precise calculations are necessary because shingle pieces will need to change shape and become narrower as you move from the base of the cone up to its peak.

Cutting the shingles is a task you can do ahead of time, by creating a template, or when you get to a particular part of the installation.

Safety Concerns

Because cone-shaped roofs are usually steep and high off the ground, consider hammering footholds into the roof for stable support while you work. Better yet, use scaffolding, which not only provides a platform for leaning a ladder onto the roof, it also serves as an easily accessible shelf for your roofing materials and tools.

On a flat-sided cone roof, use the standard hip and ridge installation method. (Copyright Asphalt Roofing Manufacturers Association, reprinted with permission.)

Underlayment and Ventilation

With preparations complete and safety equipment in place, you’re ready for the fun part: installation.

First, start by applying a good quality underlayment to the deck per the manufacturer’s instructions.

The underlayment should be applied vertically, perpendicular to the eave, following the flow pattern from the cone’s peak to its base. This process will help to prevent the material from wrinkling or buckling. You should end up with an overlap near the peak, which can be trimmed during underlayment application and before installing shingles.

Continue to overlap the underlayment vertically as you progress up the cone and use asphalt plastic cement to cement the lap edge. Alternatively, you can use a peel-and-stick underlayment. A self-adhering underlayment protects the eaves and flashing from wind-driven rain and covers any possible gaps between abutting shingles.

Next, check the ventilation. If the cone is open to the attic area, it should be part of the ventilation system. To accommodate static ventilation in the main portion of the attic, increase the requirement for the net-free area by the same square footage as the cone-shaped room. If the area is open to the living space, a ceiling fan can help force moisture and heat from the cone-shaped room to the main living area for dispersal. Using a room dehumidifier may also be helpful.

When working with a completely circular cone, use an off-peak, roll-type ridge vent at the peak for positive ventilation. The formula for cone-shaped rooms is consistent with any other residential area:

  • Equal intake and exhaust vents: 300 square feet of attic area = 1 square foot of net-free vent area
  • Exhaust vents only: 150 square feet of attic area = 1 square foot of net-free vent area

In cases with no ventilation, make the homeowner aware of potential issues with accelerated wear and how it can affect the product’s warranty. For more specific requirements, contact the shingle manufacturer.

Shingling Flat-Sided vs. Rounded Cones

After installing underlayment and addressing ventilation, you can start applying shingles.

When shingling a rounded cone roof, divide the roof into three distinct zones. (Copyright Asphalt Roofing Manufacturers Association, reprinted with permission.)

If you’re working with a flat-sided cone roof, you can use the standard hip and ridge installation method. Snap vertical chalk lines from the cone tip to the eave center on each of the flat sides. Then apply shingles to the flat areas, cutting at the hips or joints. Use a standard hip and ridge shingle to complete the hip joints.

To ensure a continuous roofing line, snap horizontal chalk lines around the cone so that shingles will line up on adjacent sides.

Shingles on steep-sided cone roofs — those greater than 21/12 slope — may need to be hand sealed with asphalt plastic cement. Check the manufacturer’s instructions for steep-slope application.

When shingling a rounded cone roof, you won’t have a horizontal line to follow because of the curvature. If you try to create a line, butting the sides of the shingles together, the shingles will gradually curve downward and won’t correctly align when you encircle the cone.

To make installation easier, divide the roof into three distinct zones. Start applying shingles to zone one, at the bottom of the cone, and then work your way up to zones two and three.

While you are nailing, have another crew member help hold the shingles down around the curve so they are flush against the surface.

Side overlap of shingles is more noticeable in the upper portions of each cone. Trim shingles at an angle to make the joint parallel to water flow. (Copyright Asphalt Roofing Manufacturers Association, reprinted with permission.)

Because the cone shape tapers from the base to the peak, succeeding courses require less material.

The degree of horizontal offset and varied shingle cutouts will create a random appearance. When using standard three-tab shingles, trim each shingle for proper vertical alignment. A simpler alternative would be to use a randomly applied shingle that doesn’t need to be vertically aligned.

Shingling a cone-shaped roof may be challenging, but with the proper knowledge and execution, you can restore this architectural focal point to its full glory.

For more information from Atlas Roofing, including technical bulletins, installation instructions and product data sheets, visit atlasroofing.com.

Three Shingle Installation Mistakes That Cause Major Problems

By following installation guidelines, contractors can produce a more professional-looking roof that will be far less likely to experience problems a year, two years, or even 10 years down the road.

A roof that isn’t installed precisely the way it was intended can be both unattractive and incapable of standing up to extreme weather conditions. On a laminate shingle roof, overlooking seemingly small details, such as shingle alignment and nailing, can lead to serious problems. Here are some of the most common details that, when improperly executed, can have negative consequences later in the installation or after completion of the roof:

  1. No Starter Shingles/Improper Alignment of Shingles at Eave and Rake

CORRECT: This photo shows the starter shingle being installed correctly. Proper alignment is crucial when installing the starter shingles. Photos: Atlas Roofing

The starter shingle’s two purposes are water protection and wind protection at the eave and rake. A starter shingle is used to seal with the field shingle at the first course along the eave and rake. This helps prevent wind and water from getting beneath the shingle in this critical location. The underlayment is a secondary water barrier if any moisture gets beneath the shingles.

Starter shingles are installed so they overhang the edge of the eaves slightly to allow for water runoff. Then a course of shingles is installed on top of the starter shingles, forming a front line of defense for blow-offs and water damage.

INCORRECT: When starter shingles are not installed, water channels can form where the shingles align across the first course. Photos: Atlas Roofing

When roofers don’t use starter shingles and install the first course of shingles directly onto the eave or rake, water channels can form where the shingles align across the first course. Moisture can then come into direct contact with the roof deck. Shingles farther up the roof are protected by the courses beneath them, which catch and divert any water that happens to drip between the edges. The first course of shingles needs the same defense from the elements.

Tip: Proper alignment is important when installing both the starter shingles and the first course of shingles. If the starter shingles are not secured correctly at the eave or rake, and the first course of shingles is not nailed down evenly across the top of the starter shingles, the roof may be at risk for wind and/or water damage.

Manufacturer’s guidelines for the proper overhang spacing at the drip edge or rake should be followed precisely. If the starter shingle overhangs the eave too much, a gust of strong wind may lift the shingles and cause a blow-off.

  1. Improper Nailing

The obvious purpose of proper nailing is to ensure that shingles stay in place and don’t cause leaks. Local building

INCORRECT: Nail heads should be flush with the top of the shingle. All three of the nails in this photo are incorrectly installed. The nail on the left is over-driven, the middle nail is at the wrong angle, and the one on the right is under-driven. Photos: Atlas Roofing

codes and manufacturers’ instructions give roofing contractors the directions they need to fasten the shingles properly to the roof deck. Guidelines specify the number of nails per shingle and where the nails should be placed.

In laminate shingles, the nailing zone is referred to as the “common bond” area of the shingle. The “common bond” area includes the double-layer portion of the shingle down to the exposure and constitutes the proper nailing area as identified in laminate shingle installation instructions. The “common bond” nailing area must be targeted correctly in order to obtain the proper wind performance as advertised by the shingle manufacturer. Properly

INCORRECT: The nailing area must be targeted correctly in order to obtain the proper wind performance. In this photo, nails are improperly placed both above and below the common bond area. Photos: Atlas Roofing

placed nails go through two layers of shingles – penetrating through the previous shingle course underneath – attaching them securely to the roof deck. Nails placed outside the common bond area can void the roof’s warranty and prevent asphalt shingles from performing as intended during extreme weather.

Tip: Pneumatic nail guns are popular among many roofers. The pressure on the gun should be set correctly before use. Nail heads should be flush with the top of the shingle. If the pressure is set too high, the gun will overdrive the shingle, causing it to sink into the mat. Too low, and nails will be under-driven, meaning they will stick out above the top of the shingle. Incorrect pressure can also cause nails to be driven in diagonally.

Wind and wind-driven rain can lift improperly nailed shingles and cause water damage to the roof and possibly blow-offs. Using either too many or not enough nails can weaken the shingle’s performance, which can also result in blow-offs.

Finally, roofers who prefer hammers should be skilled enough to drive nails consistently into shingles at the right angle, not over- or under-drive them.

  1. Improper Shingle Alignment

Roof shingles are intended to be precisely aligned, both vertically and horizontally. Roofers lay out each course of

INCORRECT: Proper alignment of the shingles is crucial. In this photo, the top shingle has been placed too high. Photos: Atlas Roofing

shingles in a staggered, stepped pattern (think of a brick wall). The shingle edges of one course must be offset from the shingles below. Edges lined up with each other would allow water to seep through to the roof deck.

INCORRECT: The shingle at the top of this photo has been placed too low. Photos: Atlas Roofing

Installing shingles too high or too low compared to the previous course can affect the exposure, which in turn would affect the aesthetics, wind performance and seal strength of the roof. An improperly aligned shingle course would be very noticeable and have a wavy appearance that is unattractive and amateurish.

Tip: Manufacturer’s instructions for proper shingle alignment are printed on the shingle wrapper.

Eliminating Problems Pays Big Dividends

Roofers who are careful to avoid these mistakes can avoid unintended problems after installation. Using a starter shingle at the eaves and rakes can ensure that the installation is off to a good start. Paying attention to proper nailing and nail placement within the common bond area on all courses all the way up to the ridge can optimize the roof’s performance against wind and rain. Finally, carefully aligning each course of shingles both vertically and horizontally will give the finished roof a professional appearance and help to improve the homeowner’s curb appeal.

Replacing a Roof Drain on a Structurally Sloped Steel Roof Deck

Figure 1. Roof drain detail. Photos: Hutchinson Design Group Ltd.

What is the number one goal of any building owner when it comes to the roof? They don’t want water pouring through their ceilings damaging the interior of the building. How do you keep water out of the building? By keeping the water on the exterior of the building and directing it to the roof drains or other drain locations, such as scupper or gutters. The roof drain is, on a basic level, one of the simplest details on the roof, and yet it is flashed incorrectly time and time again. This paper will walk you through the process of replacing a roof drain on a structurally sloped steel roof deck and installing the new roof system and flashing.

Photo 1. The sump pan and drain body have been installed. Photos: Hutchinson Design Group Ltd.

First off, we are going to assume that the current drainpipe is adequate to handle the existing water volume and drain its portion of the roof, and that the drain pipe is in good condition. Our new roof system will meet the current R-30 requirements for continuous insulation above the roof deck in a roof near Chicago. So, our roof system will be composed of a mechanically fastened substrate board on the steel roof deck, a self-adhering vapor retarder, two layers of 2.6-inch insulation mechanically fastened, a 1/2-inch modified gypsum cover board set in bead foam adhesive, and fully adhered EPDM membrane. (See Figure 1.) We will also assume that the roofing contractor is acting as the general contractor for our scenario.

Now that we have our parameters out of the way, what’s first? I have never met a building owner that likes construction debris inside of their conference room or classroom, so the interior needs to be protected prior to the removal of the existing roof drain. This can be as simple as some Visqueen, but the interior protection needs to be installed prior to the removal of the existing roof drain. The one question that seems to come up is, who is installing this protection? The owner? The plumber? The roofing contractor? I like to put this on the plumber. He knows when he is removing the drain and installing the new one.

Once the interior protection is installed, we need to coordinate the removal of the existing roof system and installation of the vapor retarder with the removal of the existing roof drain, as well as the installation of the new metal sump pan, drain body and lead and oakum joint to the existing drain pipe. (See Photo 1.) This all needs to be done on the same day so that the roof can drain properly and that the vapor retarder can be terminated onto the roof drain flange. This part is critical, as with experience this designer has learned that the vapor retarder can be used as the seal between the extension ring and the roof drain flange and that the O-ring can be eliminated. The sump needs to be fastened to the roof deck around the perimeter at 8 inches on center and be centered on the drainpipe. The drain body then needs to be set over the drainpipe and lead and oakum installed between the drain body and drain pipe.

Installing the New Roof

So, now we have the roof drain body and the vapor retarder installed. Now comes the new roof system. To meet our R-30 requirements, we are going to need a base layer of 2.6-inch polyisocyanurate insulation and 4-foot-wide, 1/2-inch-per-foot tapered insulation sump around the roof drain. This sump will get us to the R-30 requirements of 4 feet from the roof drain as required by the current codes. If my math is correct, that will leave 3.1 inches of insulation at the roof drain. We will need a reversible collar and threaded extension ring to accommodate this height. When setting the reversible collar onto the drain bowl, set it in water cut-off mastic. If the drain ever becomes clogged, this will help to keep water from seeping under the reversible collar and into the roof system. Next the threaded extension ring is installed. First, install some water cut-off mastic onto the treads prior to engagement with the reversible collar. Once again, this will help to prevent water from entering the roof system if the drain becomes clogged and backs up.

Photo 2. The extension ring has been set lower than the cover board (yellow) and water cut off mastic has been installed on the extension ring flange. Photos: Hutchinson Design Group Ltd.

One of the main questions that I receive from the roofing and plumbing contractors is, “How high should I set the extension ring?” Well, it varies per roof system, but for our scenario it needs to be set flush with the top of the tapered insulation. We set it here because we have our cover board that has yet to be installed, and when the clamping ring is installed it will be lower than the cover board. Now back to the insulation; the 2.6-inch insulation should be installed as close to the extension ring as possible, chamfered as required to fit under the flange. Next the tapered insulation sump is installed. This should be installed as close as possible to the extension ring flange and chamfered as required to fit beneath the flange. All voids between the extension ring and the insulation should be filled with spray polyurethane foam insulation.

Once we have our insulation installed, next comes the cover board. The number one thing with the cover board and roof drain is having the cover board cut perpendicularly to the roof drain flange. (See Photo 2.) Do notchamfer the cover board. Chamfering the cover board may ease the transition of the membrane onto the extension ring flange, but it creates an unsuitable substrate surface for the bonding adhesive. And in my experience, water seems to end up ponding around the roof drain and not dropping into the roof drain. This will also allow the roof’s drain clamping ring to sit flat and below the roof surface of the roof.

Photo 3. The membrane has been correctly cut in a cloverleaf pattern. Photos: Hutchinson Design Group Ltd.

Now that our cover board is installed, we have the membrane and its transition into the roof drain. Water cut-off mastic is to be installed on the extension ring flange. How much you ask? One tube. Load that flange up. Make two thick beads with it. I have never heard a contractor say, “Man, using all of that water cut-off mastic on the job really set me back.” It’s a small item, but it is worth it.

After the membrane has been installed and the clamping ring is set, it’s time to cut a hole in the membrane to allow the water to get to the drain and off the roof. How big should the hole be? As small as possible is what some contractors might say. I ask a question to you now: what is the goal of the roof drain? If you answered to get the water off the roof as quickly as possible, you would be correct. Then why would the contractor want to cut a small hole in the roof membrane that would restrict the flow of water into the roof drain piping and off of the roof? I am dumbfounded as well. When we detail the roof drain, we call for the membrane to be cut back to within a 1/2 inch of the extension ring in a cloverleaf pattern around the clamping ring bolts. (See Photo 3.) This way there is no confusion on how far back the membrane is to be cut. Set the drain dome and the roof drain detail is complete.

So, there you have it. Now the roof can drain properly with a brand-new roof drain with no problem (fingers crossed).

Fact or Fiction? Mixing Exhaust Vent Types Is Problematic

Too often, attic exhaust vent types are mixed, which can short-circuit the airflow pattern in the attic space. Photo: Jerry Becker

Airflow dynamics dictates avoiding it. The manufacturers’ Installation Instructions caution against it. Building Code cites it as a violation. And yet it remains one of the most questioned, challenged and, unfortunately, ignored tips offered during our best practices in residential attic ventilation seminars.

Is it really a problem to mix or combine different types of attic exhaust ventilation (ridge vents, wind turbines, gable louvers, box vents and power fans) on the same roof above a common attic? And if it is, why will you see it so often driving through any city in North America?

Lack of information, misunderstanding the science, and resistance to breaking old habits all contribute to the persistence of mixed exhaust vents on today’s roofs. We asked roofing contractors to share their experiences to help explain what could go wrong.

Problem No. 1: Inefficient Airflow

The main reason combining different types of exhaust vents is problematic is that it disturbs the proper flow of the attic air. To best help fight heat buildup, moisture buildup and ice dams, attic ventilation must be a balanced system of intake vents (placed low on the roof in the soffit or at the roof’s edge) and exhaust vents (placed at or near the roof’s peak). This allows the incoming cooler, drier air to enter the attic at the lowest possible location, flush out any built-up heat and moisture from inside the attic all along the entire underside of the roof deck, and push it out through the exhaust vents high on the roof.

Power fans are a good exhaust vent option. So are ridge vents. But not when they are mixed together on the same roof above a common attic. Doing so could lead to inefficient airflow and weather infiltration. Photo: Sean Toms

But, if two or more different types of exhaust vents are in place, it short-circuits the system. Instead of the primary path of air being into the intake vents and out of the exhaust vents, the path is mostly between the two styles of exhaust vents. One of the types of exhaust vents becomes an intake vent because air will always follow the path of least resistance. Air will always look for the easiest, closest path to take. That path happens to be between the two types of exhaust vents. And that limits the distribution of the air to the upper region of the roof; or worse, it keeps the air circulating between the distances of the two vents closest to the peak. That is not the best way to remove heat and moisture buildup inside an attic.

“About five years ago, I had a seasoned roofer with me that just started working for our company,” recalls roofing consultant Jerry Becker, Roof Life of Oregon, Tigard, Oregon. “We walked up to this apartment complex and I noticed that there was a power fan alongside can vents (box vents) and very little intake ventilation. I placed a friendly bet with him stating that I know what the plywood already looks like underneath without looking at it. He argued with me and said, ‘This roof has plenty of ventilation; look at all the vents up top and it even has a fan!’ So, I told him that the plywood next to the fan and the closest can vents and up to the ridge is going to be perfect, but as soon as you drop down about a foot from the power fan the plywood will be as black as night.

“We go inside the attic and what do you think we found? Black microbial growth on the lower section of the roof. It was so black that it was wet. It is important not to mix exhaust vent types. It’s bad enough when you do it on a single dwelling home, but that same mistake in a multi-family home is deadly. Think of all the moisture that is created by all the families — the washer/dryer, dishwasher, sinks, showers and ourselves.”

Inefficient airflow not only can damage the roof deck but it can also prematurely age the asphalt shingles. “I see examples of this all the time,” says Trevor Atwell, owner, Atwell Exterior Services LLC, Greenville, North Carolina. “Premature aging of roofing materials, buckled sheathing and signs of rotten wood all due to the moisture and heat being trapped.”

Ironically, sometimes the desire to mix types of attic exhaust vents seems reasonable on the surface. The homeowner or the roofing contractor wants to improve the flow of air. Thus, adding more vents — even if they are different types — seems logical. But more is only better in this case if it’s more of the same type. If improved airflow is the goal, double-check if the correct type of exhaust vent is being used to match the size and design of the roof/attic and if it’s being supplied with a balanced amount of intake ventilation. Mixing exhaust is not the solution.

Box vents or power vents installed near a ridge vent can lead to inefficient airflow, which can damage the roof deck and prematurely age asphalt shingles. Photo: Trevor Atwell

“I have seen this in action and until it was explained to me why I should avoid it, the concept of mixed exhaust was a mystery I had to punt to a colleague or competitor” says Tim Chapin, owner, Your Safe and Healthy Home, Akron, Ohio. “I had a condo project with a very complex roof made even worse by the presence of ridge vents, gable vents, soffit vents, and box vents. I was amazed there was a problem because it seemed to be ventilated to the max. But now I know it was short-circuited.”

“We see it often with ridge vents and a power fan just below the ridge vent, or with box vents combined with ridge vents; sometimes all three. We call it the Ventilation Trifecta,” says Tom Picha, steep slope consultant, Affordable Roofing Inc., Aurora, Illinois. “More is good in some cases. Not all.”

“I had a house I was asked to inspect. The house had a ridge vent, box vents and vented drip edge on it,” says Jeffrey Heitzenrater, owner, Triple Peaks Roofing & Construction Inc., Westlake, Ohio. “The first thing wrong was two different types of exhaust vents. Upon a complete attic inspection, we found mold and mildew. The insulation was also packed tight at the bottom, blocking off the intake system the previous company installed. This particular roof was only eight years old and all the plywood is now bad. This was caused from the trifecta — no intake, box vents turning into intake and venting out of the ridge vent.”

Problem No. 2: Weather Infiltration

When you ask a vent to perform a task it has not been designed to tackle, you’re rolling the dice against Mother Nature. An exhaust vent mixed with another type of exhaust vent that suddenly is pulled into intake airflow duties as a result of short-circuiting is not only pulling in air, but whatever the air is carrying that very moment: rain, snow, debris. Exhaust vents are not designed to ingest anything.

One of the consequences of mixing attic exhaust vent types can be weather infiltration, such as the snow in this photo. Photo: Ron Bastian

“In the winter when freezing rain turns into fine ice particles, I observed several times the lower exhaust vents on the roof becoming intake vents instead of exhaust as designed and drawing in ice particles and snow,” says Steve DuCharme, owner, Innovative Builders Roofing & Construction, Edmond, Oklahoma.

“I have witnessed snow ingestion into the attic due to mixed exhaust vents,” says Corey Ballweg, owner and president, Mid Towne Construction Inc., Cross Plains, Wisconsin.

“I recall an attic several years ago that had ridge vent and two power fans. They installed two because they were told one wouldn’t pull enough heat out,” says Paul Vosen, president, Degenhardt Home Improvement, Madison, Wisconsin. “The house had no overhangs and the attic floor was insulated with a good vapor barrier. I was there in the rain and both power fans were running. The attic was so tight that the power fans were actually pulling rain in through the ridge vent. Never have I seen that before — nor have I seen it since, but I never forgot it.”

The weather infiltration problems that can result from mixing exhaust vent types may not catch a homeowner’s attention right away. Not many homeowners regularly check their attic.

“I worked on a roof that did not have any intake vents at the soffit but did have two gable vents in addition, a power fan, and four box vents,” says Scott Dennison, president, Dennison Exterior Solutions & Gutter Topper, Saint Joseph, Michigan. “Over the brief 15-year life of the roof, when the power vent would turn on it turned the four box vents into intake vents which sucked water into the attic and destroyed the roof deck adjacent and below the vent.”

The most common exhaust mixture our seminar attendees tell us they see: gable end louvers combined with something else. Often the homeowner demands that the roofing contractor leave the gable end vent in place despite the fact a ridge vent is being installed as an exhaust vent improvement. The homeowner’s reasoning: The gable louver adds a decorative touch to the home’s exterior. Solution: Do what Ron Bastian does.

“I’ve noticed snow and wind-driven rain coming in a gable end vent which was combined with a ridge vent,” says Bastian, owner and president, Bastian Roofing Inc., Richfield, Wisconsin. “We closed up the gable end vent from inside the attic and this cured the problem I was called out for.” By closing up the gable vent from inside, the attic short-circuiting is eliminated and the homeowner can still enjoy the cosmetics from the exterior.

“We have witnessed numerous issues related to short-circuiting,” says Shawn Bellis, owner, EPIC Exteriors, Overland Park, Kansas. “We’ve seen fine wind-driven Midwest snow sucked into the exhaust vents — gable vents mixed with ridge vents, for example.”

There’s a Much Better Way

Inefficient airflow, mold, rotted decking, prematurely aging shingles, and weather infiltration into the attic does not have to be the final outcome. There’s a better way, but it may take a commitment to educating the homeowner and fellow roofing contractors. I believe that’s one of the reasons our best practices seminars are so well received.

“I had mixed attic ventilation on my own home,” says Sean Toms, quality control inspector, S & K Roofing, Eldersburg, Maryland. “After attending the seminar a few years ago, I looked in my attic. I had condensation on the roof nails. I had a ridge vent, fully vented soffit and gable vents. I closed the gable vents and added insulation to my attic floor. Problem solved.”

“I seem to run into mixed exhaust vents every week. Homeowners think that the more types of ventilation on the roof the better they are,” says Richard Turner, owner, RJ Turner Remodeling, LLC, High Point, North Carolina. “After explaining the things I have learned in the Air Vent Inc. seminars, they quickly understand the correct way things should be done.”

About the Author: Paul Scelsi is marketing communications manager at Air Vent Inc., and leader of its Attic Ventilation: Ask the Expert™ seminars. He’s also chairman of the Asphalt Roofing Manufacturers Association Ventilation Task Force. For more information, visit www.airvent.com.