What causes blisters on a flat roof?
When moisture seeps between the plies of a roofing system, and then the sun comes out and heats up the surface, the water turns to vapor. Expansion of the trapped gas causes a raised pocket, known as a blister, to form. The weather can cause the blister to grow on a daily basis. Warm weather will cause the water or air to expand during the day. The cool temperature will cause the trapped water or air to contract at night. The blister will often loosen and stretch the covering in this area, allowing more deterioration, and leakage to occur.
Inspecting blisters on a flat roof
Some blisters may be found open, but the vast majority may not ‘pop’. Should we recommend repair / replacement of the entire roof covering? Or do we recommend ongoing maintenance and inspection all of the blisters discovered and repair for only the blisters that have opened?
Although everyone appears to agree that if a blister has opened, it must be fixed, the industry does not give a succinct response to this subject. This is due to the likelihood of moisture entering the system at these points. The choice to fix unopened blisters has always been left to the contractor’s discretion.
Flat Roof Blisters 1
To Repair or Not Repair?
Repairing blisters on a traditional low-slope membrane system is essentially a matter of judgment. Your choice will be influenced by the size, type, and frequency of blisters. They also have the potential to reduce the roof system’s service life. When repairs are made as part of a maintenance program with the goal of extending the system’s service life, it may be better to finish them. If more insulation is needed, the patched membrane might be used as an air and vapor barrier.
Additional reference websites:
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National Roofing Contractors Association Home – NRCA
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National Federation of Roofing Contractors (NFRC)
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EPDM Roofing Association: Home
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Welcome to The Single Ply Roofing Association | SPRA
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Last Updated on 4 years ago
