Q. I am having a major room addition to my house. In my past two houses, the shingle roofs leaked prematurely. What should I look for and discuss with the roofers?
Most roofs that leak prematurely are more often a result of poor installation rather than material defects. If you choose high-quality shingles from a major manufacturer, there will be very few material flaws. When a roof is installed properly, there are usually several layers of protection, so one small material flaw should not create a significant leak.
The first step is to make sure you have a “smart” roof design. Your roof should be designed to avoid valleys that drain against a sidewall, misdirected gutter spouts and excessively complicated roof angles and valleys. Chimneys can sometimes be located as an afterthought, and they may block the free flow of the water.
It is important for you to stress quality installation to the builder for the roof sheathing and the use of enough nails. If the sheathing is not attached securely, the edges can curl and expand as they absorb moisture during humid seasons and heavy rains. When they dry out, the sheathing shrinks back again.
This repeated movement of the sheathing often causes nails to slowly work their way out of the sheathing and rafters and trusses below. The nail head literally can move up enough to slightly puncture the shingles and result in a leak over time.
Aligning the shingles
Try to be present when the roofers start installing the shingles, because misalignment of the starter course of shingles can result in leaks. The butt joints between the first course of shingles should be offset from the starter course butt joints. If they are aligned, there can be a leak every several feet, which may cause dampness and rotting in the walls and rafter ends.
Proper fastening of the shingles is also critical for a leak-free roof, particularly in areas with high winds, which can lift loosely applied shingles and allow water to get under them. In these parts of the country, a storm-nailing schedule of six nails per shingle is often a wise method.
Using enough nails
Some typical nailing problems are using too few fasteners or locating them improperly on the shingle. If they are either too high or too low on the shingle, leaks may occur. When staplers are used, the staples should be shot in perpendicular to the shingle. Sometimes they are shot in vertically because this is a quicker and convenient tool position. The shingle wrapper should list recommended nailing guidelines for those specific shingles.
When step flashing is installed along a chimney or other wall, the pieces of sheet metal should be properly sized and aligned with the top of the shingles. The flashing should be nailed only once in the top corner and overlap the next piece by a couple of inches.
One final problem can occur by improper handling of the shingles. Some roofers place the bundle of shingles over the peak of the roof. This causes them to bend, and it may weaken them at the location of the bend. This is a particularly bad practice during cold weather. The bundles should be placed flat on the roof.
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