Roof leaks

Published on January 13th, 2013 | by Henri

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Asphalt roll roofing is blistering

Q. I am a longtime, enthusiastic reader of your column and blog, and need your advice with the roof on our addition. Three years ago, we had the roof on our addition replaced. Because of the low pitch (1.25″ for every 12″) and the necessity to be able to walk on it once or twice a winter after extra-heavy snowfall, asphalt-roll roofing was recommended by the roofer. Now the surface is blistering and a few of the blisters have popped, creating mini-craters in the roofing surface.

Is this “normal” wear and tear, or was inferior material used that we should complain to the roofer about? What is the normal life of a roof with roll roofing before it needs to be replaced? Are there alternatives for our type of roof that you would recommend?

A. I would not call what happened to the roll roofing on your addition’s roof “normal” wear and tear after just over two years; something is wrong there.

Blistering is generally caused by moisture trapped under the roofing material, or by moisture that saturates it, gets heated by the sun and turns into steam, particularly if the material is black. This problem may be because water got under the roofing material at seams that weren’t properly sealed or it may be that the deck was not fully dry at the time of application of the material. The normal life of roll roofing is 10 years.

Before I can recommend a far better substitute, I have to question why you need to walk on the roof after heavy snowfalls to remove the snow. The addition should have been built to withstand the live loads of snow accumulation in your area. Removing snow from a roof is likely to damage the roof surface and this may be a contributing factor to the problems you have.

The best roof covering for a flat or low-slope roof is a synthetic rubber roof such as EPDM or Trocal but it should not be subjected to snow removal.

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