Manufactured products typically come with installation instructions. If the installer follows them, one would presume the warranty would stand. But one Virginia Supreme Court case, Bridgestone/Firestone v. Prince William Square, 250 Va. 402, 463 S.E.2d 661 (1995), calls that presumption into question.
In that case, the installer installed per manufacturer's instructions. Although the installer used fasteners not furnished by the manufacturer, the manufacturer inspected and accepted the roof, and the fastener use was per the instructions. But after several years of responding to warranty claims for leaks, the manufacturer claimed its warranty was void because the installer used the fasteners that the manufacturer did not furnish.
The lower court rejected that claim, but the Virginia Supreme Court agreed with the manufacturer because it concluded the written warranty terms were clear that the manufacturer only agreed to repair leaks caused by workmanship or materials it supplied and it had not supplied the fasterners that had been determined as the cause of the leaks. The court refused to consider the installation was consistent with the installation instructions and by an authorized applicator of the manufacturer, and instead applied the warranty strictly as written.
Bottom line, warranties need to be carefully reviewed to verify the exact terms and conditions of the warranty, and that language you think might be insignificant could very well be the deciding factor in whether the warranty exists or has been voided.