Highs and lows of tar and gravel roofing
QUESTION: We own a home that was built in 1964. We love many aspects of the home, especially its unique design. It has a 2/12 pitch roof that has the original tar-and-gravel material. We feel like the time has come to review our options to have the roof redone. Is there a new product that could insulate as well as act as a new roof? We don’t have attic access, so using traditional insulation is not an option. Looking forward to hearing from you. Bev Loewen
Answer: There are often new building products that come onto the market that have limited value, especially in our cold northern climate. While the roofing material best suited for your home has been around for many years, insulation upgrades done at the time of reroofing are newer and have been quite successful in reducing moisture issues in vaulted roof systems.
Homes with low-slope roofs built around the time of yours often have issues with condensation and moisture intrusion, or leakage due to roofing that has exceeded its life expectancy.
Built-up roofing systems, commonly called tar and gravel, are very high-quality products that have been used successfully for many decades on low-slope and flat roofs. Unfortunately, these systems are extremely labour intensive as they require multiple layers of roofing felts and hot tar to be applied. Once this membrane is sufficient in thickness, the top layer is typically covered with a layer of small, round stones. This stone layer prevents damage to the roofing from mechanical forces, while protecting the bitumen layers from harmful UV light from the sun. Because of the difficult and timeconsuming installation process, other more modern roofing systems have been developed.
The most commonly used of the newer low-slope roofing systems, is often referred to as a single-ply membrane.
While this name is somewhat misleading, it does differentiate between the multiple layers of the tar and gravel roof. Single-ply roofing is normally a rubberized membrane with a bitumen-based underside and coloured granules on the top surface that is partially overlapped. The granules look similar to those in common asphalt shingles and protect the layers underneath from the sun and physical wear. These membranes may be attached to the roof deck by melting with a large propane torch, or many are self-adhered by peeling off a protective layer and directly applying to the roof sheathing. While the torching method is still somewhat labour intensive, and dangerous, the self-adhesive membranes can save time and money. That is why they may now be the most commonly materials used for these style of roofs in our area.
There are other single-ply roofing materials available, but for residential use, the granule-covered membranes are the standard due to their ease of application and appearance.
Workers mop hot tar on a roof. Although this application is the best way to cover low-slope roofs, it can be costly and labour intensive.