A bubble in a torch down roof is a pocket of trapped air or moisture between layers. A few small, unbroken blisters are usually watched rather than cut; broken or spreading ones need repair. MLM Construction Group repairs Brooklyn flat roofs, HIC #2130570, with 97 Google reviews at 5.0. Call (516) 713-9199.
Most flat roofs on Brooklyn row houses and small apartment buildings are torch applied modified bitumen, usually called torch down. It goes on as rolls that are heated with a torch until the underside melts and bonds to the layer below. Done right, the layers become one continuous sheet.
A blister is a spot where they did not. A pocket of air or water vapor is trapped between the plies, or between the membrane and the base below, and it rises into a dome. Some are the size of a coin, some are a few feet across, and on a hot day they swell and feel soft underfoot.
Moisture is the usual cause. If the deck or the old roof underneath was damp when the new membrane went on, that water is sealed in. When the sun heats the roof the moisture turns to vapor, expands and lifts the membrane where the bond is weakest.
Workmanship is the other cause. If the torch did not melt the underside evenly, there are spots that never bonded, and air trapped there behaves the same way. Roofing over an existing roof without removing it, which is common on older Brooklyn buildings, adds more layers where moisture can hide.
Blisters usually show up in the first summer or two after a roof is installed, which is why they are worth a look under a new roof's warranty.
A small blister with an intact surface, no cracks and no granule loss is often best left alone and watched. Cutting it open creates a seam where there was none, and a repair is a potential leak. Mark it, photograph it with something for scale, and look again next season.
If it stays the same size and the surface stays intact, it is a cosmetic defect, not a leak.
Repair any blister that is cracked, broken, or has lost its granules on top, because the membrane there is now thinner and exposed to the sun. Repair blisters that are growing season to season, and anything in a spot that gets foot traffic, like the path from the bulkhead to the AC units, because a soft blister that gets stepped on splits.
The repair is to cut the blister open, let the inside dry out, bond the layers back down, and torch a patch over it that extends well past the cut on every side. Done properly, that spot is as good as the rest of the roof.
One or two blisters are a local defect. Dozens of them, or blisters together with soft spots, ponding and leaks inside, point to moisture trapped across a large area of the roof. Cutting and patching them one by one does not fix that, because the water stays under the membrane and keeps lifting it.
At that point the honest question is how much of the roof is wet. Test cuts in a few places answer it. If the moisture is widespread, the wet layers have to come off, and that is a replacement conversation rather than a repair.
Cold weather makes the membrane stiffer, and a blister that was soft in August can crack under foot or under snow load in January. If you have bubbles on your roof, now is the time to find out which kind they are.
MLM Construction Group inspects and repairs torch down and other flat roofs across Brooklyn, Queens and Manhattan, licensed under NYC DCWP HIC #2130570 and fully insured. See our flat roofing page or call (516) 713-9199.
Trapped moisture or air between the layers of the membrane, or between the membrane and the surface below. Moisture sealed in during installation turns to vapor when the sun heats the roof, expands and lifts the membrane where the bond is weakest.
Small blisters with an intact surface are often cosmetic and are best watched rather than cut. Blisters that are cracked, losing granules, growing, or in foot traffic areas need repair, because the membrane there is thinner and can split.
Not yourself, and not if it is small and intact. Cutting creates a seam that has to be properly patched. When a blister does need repair, it is cut, dried, bonded back down and covered with a torched patch extending well past the cut.
Not by themselves. A blister is a pocket under the surface, and the membrane above it may still be watertight. Leaks start when the blister cracks or splits, which is why broken blisters should be repaired promptly.
Usually because the deck or old roof was damp when the new membrane was installed, or because the torch did not bond the membrane evenly. They often appear in the first summer or two, so check whether your roof warranty covers them.
When there are many of them together with soft spots, ponding or interior leaks, it points to moisture trapped across a large area. Test cuts show how much of the roof is wet. Widespread moisture means the wet layers must come off.
Yes. MLM Construction Group repairs and replaces torch down modified bitumen roofs across Brooklyn, Queens and Manhattan, licensed under NYC DCWP HIC #2130570 and fully insured. Call (516) 713-9199 for a free assessment.