The shingles on your roof serve a dual purpose. They give the roof a finished look, while forming a protective seal. Lumpy, bumpy or curling shingles that do not lie flat can be problematic, but don’t hire a new roofer yet. The extent of the problem depends upon many factors, including the age of the roof, the outdoor temperature and the overall condition of the roof. In some cases, the shingles will almost magically fix themselves, but in other cases, costly repairs might be necessary.
New Shingles Not Sealing Down
Standard asphalt shingles feature an adhesive strip that softens during warm weather, especially when the sun’s rays hit the roof directly. When the shingles heat up, they become flexible and the adhesive bonds the shingles in place. Before new shingles seal down, they can look a little lumpy and uneven, but once the roof gets hot enough, they should soften, flatten and form a permanent seal. Sometimes this problem is more apparent on north-facing roof slopes that don’t heat up sufficiently for the shingles to seal until summer. Usually this isn’t a major issue, but if you live in an area that is very windy, your roofer can apply temporary adhesive to prevent the wind from catching the edge of the unsealed shingles and blowing them off.
Multiple Layer Roofs
Most communities have building codes that prevent homeowners and roofers from installing more than two layers of shingles. It’s always better in the long run to tear off the old layer of shingles before installing the new layer. But tear-offs add substantially to the cost of reroofing projects, so some homeowners opt to install new shingles over old ones. Once the new layer of shingles seals, the new shingles will conform to the configuration of the old roof, including its bumps and dips. While this may not be attractive, as long as the new layer of shingles bonds, it will protect the roof beneath.
Before installing a second layer of shingles over a first layer, the roofer should examine the old roof, sweep away all debris and countersink any nails that might be sticking up. In addition, the roofer should install a layer of heavy roofing felt over the original shingle bed, which will minimize surface distortion.
Faulty Installation
If you can see voids or gaps beneath the bottom edges of the shingles, even after the roof has had a chance to seal, the problem might be due to faulty installation. New shingles come with a nailing guide, which resembles a horizontal strip on the top of each shingle. When the roofer positions the shingles as directed by the manufacturer and inserts the nails only in the nailing guide, the next row of shingles will cover the nails on the first row and seal down correctly. Incorrectly nailed shingles can permit the layer beneath to slip slightly, which can result in uneven shingles.
Lapping shingles is another installation error often made by do-it-yourselfers or unreliable roofing companies. Shingles should be butted snugly side-by-side in each horizontal row. Lapping the shingles can prevent the shingles from sealing. Before hiring a roofing contractor, ask for references to ensure the contractor is reputable.
Faulty Shingles
To ensure your shingles lie flat, you should purchase quality shingles from a reputable lumberyard. Inexpensive brands can be thin or easily damaged, or they may not contain sufficient adhesive to seal down properly. Professional roofers often choose only the shingle bundles from upper layers of the pallet. The bundles on the bottom layer sometimes conform to the shape of the wood slats on the pallet, causing them to warp. Warped shingles might seal down eventually, but they’re more difficult to install, and the gaps that result are more likely to catch the wind and cause the edge of the shingle pull away from the surface.
Options
For shingles installed during the winter, wait until warm weather to determine whether the shingles will eventually seal. Call the roofer if you believe either the installation or the shingles themselves were faulty. The shingle manufacturer posts its warranty on the wrapper of every bundle of shingles, but if the roofer did not follow the installation instructions carefully, the manufacturer is unlikely to stand behind the warranty. Call your local building authority to find out whether your state requires roofing contractors to guarantee their work, and for how long.
Source: SFGate