Warranties are often misunderstood by inspectors. Very seldom will any type of installation void a manufacturer’s warranty. For example, failing to properly ventilate the underside of the sheathing as per the manufacturer’s recommendations will not void the warranty, but it may lead to premature failure.
When a claim is made against the manufacturer, a couple of shingles will be removed from the roof and mailed to the manufacturer. The manufacturer will test the shingles to determine whether the problem was created by the manufacturing process. If it was not, the claim will be denied.
Only in a very few situations typically related to high-end shingles will the installation affect the manufacturer’s warranty.