Roofs have an average life of 18-22 years. In addition, your existing roof may have been installed ON TOP OF an older roof. There is a “two-roof” limit as to how many layers you can have. To do a roof correctly, ALL layers should be taken down to the substrate in order to inspect and replace plywood if necessary and make other repairs before a new roof is installed.
GAF Roofing Shingles & Materials are the industry leader in Residential Roofing Systems. They come with a Lifetime Warranty which is transferable to a subsequent owner. But even though these shingles alone are “lifetime”, there are some important “warnings” for homeowners to be aware of when considering a roofing contractor in order to get the biggest part of the lifetime warranty… the LABOR to replace the shingles!. In order for these warranties to apply, the following must be adhered to: The roof must be installed by a GAF Certified Contractor. This will then assure the homeowner that: – The installation will then adhere to GAF’s stringent installation procedures which will include GAF Weather Watch Leak Barrier Ice Dam Protection, Deck Armor Breathable Roof Protection and factory specified Shingle Nailing Positioning. Only then will the homeowner be protected for ALL future costs (including labor) for any warranty work that may be needed. This is how it must be done: 
You are now an educated buyer! Ask for GAF Certification, Insurance and a Detailed Description of the installation procedure that will match the above video. And DO NOT ACCEPT “Estimates”. These are only “guesses”. The Window People are a Certified GAF Roofing Contractor so you can be assured of a Lifetime Warrantied GAF roofing installation! And our price quotes are firm and valid for at least one year.