I have identified some common ways people void their warranty.
Incorrect installation. Manufacturers have requirements as to how their materials are installed. A contractor must use the correct tools, fasteners, and procedures. They also must be sure they are installing the roof over decking that meets their standards. Installing flashing incorrectly or using the wrong material can void a warranty as well. Finding a contractor certified or recognized by the manufacturer goes a long way to avoid warranty issues due to installation.
Skylights, Satellite Dishes, Solar Panels. Installing these additions to a roof require drilling into or penetrating the roofing surface. Doing so may void your warranty in full or in part regarding leaking.
Improper ventilation. A roof installation that doesn't include proper ventilation can void a warranty. If a roof is not ventilated, moisture can be trapped inside. It can also cause heat to build up causing premature shingle wear.
Installing the new roof over an old roof. Some homeowners or contractors want to save time or money by installing new roofing shingles over the existing roof. Doing this may negate the warranty. It can cause the new layer to bulge or heat and expand at different rates shortening the lifespan of the roofing material.
Spray foam insulation. Using spray foam installation and creating a "hot roof" without proper ventilation also causes the shingles to become to heated and have a shorter lifespan.
Debris accumulation. Leaves and other debris that might land on the roof can cause damage that can be avoided and denied coverage under a manufacturer warranty.
When doing anything that is on your roof, be sure to check the details of the manufacturer's warranty and check with the original roof installer to be sure that you don't accidentally void your warranty.
Craig Gouker Roofing has been installing quality residential roofing in South East Pittsburgh since 1991 and is the expert in shingle roof replacement.