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.”

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.

CFMA Spreads Suicide Prevention Awareness

According to a recent report released by the CDC, the construction industry has the second-highest rate of suicide (per 100,000 population). Given the male-dominated workforce and other indicators prevalent in construction, it’s imperative to bring suicide prevention to the forefront of safety, risk management, and HR discussions in construction companies.

On September 10, the Construction Financial Management Association (CFMA) joined the International Association for Suicide Prevention (IASP) and others around the world to help spread awareness and resources around the goal of preventing suicide.

CFMA’s journey to spread awareness and resources surrounding suicide prevention has covered much ground in little more than a year’s time. April 2016 saw CFMA’s Valley of the Sun Chapter hosting the first regional summit on the topic; CFMA’s Chicago, Charlotte, Grand Rapids, and Portland Chapters have similar events scheduled in 2016 and 2017. After their collaboration on a late 2015 issue of CFMA Building Profits article, longtime CFMA member, Cal Beyer, director of risk management at Lakeside Industries and executive committee member of the National Action Alliance for Suicide Prevention, and Dr. Sally Spencer-Thomas, CEO and co-founder of the Carson J. Spencer Foundation, mental health advocate, and survivor of her brother’s suicide, have gone on to author more than a dozen articles and spearhead just as many presentations throughout the construction industry. Their most recent work Construction + Suicide Prevention addresses why prevention is imperative in the construction industry and provides 10 action steps companies can take to save lives.

Stuart Binstock, CFMA president & CEO, further details, “CFMA is dedicating resources toward suicide prevention for one reason: If one accepts the premise that our members are responsible for the financial resources of a company and that the health and safety of human capital is an important financial resource, then how could we not get involved in educating the construction industry about this topic?”

The First Construction Industry Alliance for Suicide Prevention Association Member

CFMA formed the Construction Industry Alliance for Suicide Prevention to gather and disseminate information and resources, share education and programming for CFMA’s 94 chapters across North America, and promote initiatives to support suicide prevention. Most recently, the National Association of Surety Bond Producers (NASBP) has shown its support of creating a zero suicide industry by becoming the first association member of the Alliance.

NASBP CEO Mark McCallum affirms, “The conversation around suicide prevention in the construction industry has taken a leap forward with the formation of CFMA’s Construction Industry Alliance for Suicide Prevention. On behalf of our membership of surety bond producers and allied professionals, I’m proud of NASBP’s decision to commit to this cause, as demonstrated by joining the Alliance and supporting and participating in efforts to raise awareness of this critical issue. The health of the construction industry workforce is important to the well-being and competitiveness of this country, and suicide prevention among construction workers now is being made a focal point.”