Manufacturer’s hire lawyers to write warranties to prevent building owner’s lawyers from being able to collect. Most manufacturer’s require you to accept their warranty because it limits their liability. Further, warranties may be voided if an owner does not document routine preventive maintenance.
While a 20-Year NDL warranty may seem like solid protection, do not be misled. If you read the warranty, as you should BEFORE you buy a roof, you will find it excludes more than it covers. For instance if the warranty says it excludes “wind damage” that leaves you vulnerable even in typical summer storms. Require a minimum of 55 MPH coverage. Get more if you can negotiate it.
Rarely, will a warranty replace your roof system. A manufacturer once told me that No Dollar Limit means that “We will make every effort to find and repair a leak”. That means that they will only pay to patch a hole if it’s an issue covered by the warranty.
Not having to rely on a warranty is the best practice. One does this by choosing a contractor carefully and doing routine maintenance on your roof. Just as a car needs care to last, so does your roof. An owner can do the maintenance or have a contractor's service department do it for you.