I realize you receive many emails on flat roofs, however ours is a little different. My husband installed a flat roof 29 years ago on our porch, which is attached to the house. The ceiling and walls inside were all finished in cedar. We never had a problem in all those years, until last year, when a contractor was hired to do both the house and flat roof due to hail damage. The roof leaks very badly and has damaged our cedar inside, not to mention the roof itself. When my husband went up on the roof there were valleys, up and down, all over, and we were concerned it would leak. We called both the contractor and BP who supplied the material and were told this would straighten itself out and should not leak. Our question is; should the contractor have nailed the outside edges prior to putting down the tar? The roofing material sat in our garage for a few days and was installed on a nice day, so we doubt that was the problem. Do you have any ideas? Also it was installed over the other rolled roofing.
The exact type of roofing material used is unclear from your question, but I am assuming that the new roofing is an asphalt composition rolled roofing that was glued down over the old roofing with asphalt cement/adhesive. I doubt the old roofing was the original, as standard rolled roofing has a life expectancy much less than the 29 years since original construction.
Flat roofs have inherent difficulties with leaks, due to their lack of pitch and the tendency for water to pond in low areas. Any small hole or breach in the roofing and a leak will occur. For this reason, flat roofs or very low slope roofs need specialized roofing materials designed to prevent leaks. Rolled roofing is a lower quality roofing material that comes in rolls of varying length, with an approximate width or 3 to 4 feet. Some types have a substantial overlap up to half their width, and others have a smaller overlap and a wider granule covered layer. Most rolled roofing is designed for easy installation and has a limited lifespan of approximately 10 – 15 years. For this reason, it is the preferred material for homeowners doing their own roofing installation or repairs on low slope roofs.
The difficulty with this type of roofing is ensuring that the roof is fully covered and all seams, edges and protrusions are completely sealed against leakage. This may be tricky to accomplish on a clean roof deck, but extremely difficult on a deck with older, deteriorated roofing already installed. What I think is happening to your roof is straightforward. The roofers have failed to properly seal all the edges and seams in the new rolled roofing or get proper adhesion to the old roof. Water is getting underneath the new roofing, collecting in voids between the two layers and eventually working its way inside the roof.
Rolled roofing is not preferred for use by professional roofing contractors, due to its limited lifespan and potential for leakage. Other higher quality roofing systems are usually installed on flat roofs such as built up roofing, commonly known as tar and gravel, or single layer membranes like torch-on roofing. These systems are much more costly to install, due to the added labour costs involved, but will be very durable for many years, if properly installed.
Removal of the old rolled roofing should have been done prior to repairs, if the old roof was damaged or deteriorated. If the old rolled roofing was worn out, it may have had areas where the felt was exposed, granular surfaces cracked or worn and lifting seams. This is likely the case as the repairs were done after a hail damage claim. Any of these defects may account for the “valleys” seen in the new roofing as it partially conformed to the shape of the old damaged roofing.
Determining the exact type of roofing installed should be your first step in dealing with the roofing contractor. Check the invoice or call to determine whether the new roofing is a torch-on system or simply common rolled roofing. If the latter is installed, the roofing contractor should, at a minimum, have stripped off the old roofing before installing the new material. Ideally, the old roof sheathing should have been completely stripped to its bare surface to inspect for old leaks, moisture damage or loose fasteners.
Dealing with the roofing contractor that did the repairs may lead to little satisfaction, if they have already done a follow up inspection and denied responsibility for the leakage. The only solution may be to hire a roofing consultant or another roofer who specializes in flat roof installation and repairs. Many roofs on commercial buildings are flat or very low sloped and contacting a roofing contractor that does commercial work is recommended.