Highs and lows of tar and gravel roof­ing

Winnipeg Free Press - Section F - - HOMES - ARI MARANTZ

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.

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