How to replace your roof
Add a layer or start from scratch?
Your first decision: whether to put a new roof on top of your old one or whether to tear off and start from scratch. This decision will impact how much you spend on the project. Aside from your own preference, roof strength, shingle weight and local building codes determine whether you can add another layer. Usually no more than two layers are allowed.
First, check to make sure you won’t void the new roof’s warranty if you add a second layer. Metal roofing is an exception — it can be installed over asphalt. Tear-offs require more labor, which means it will cost more.
Consumer Reports says a complete replacement costs $100 or more per 100 square feet. Tear-offs are also messier, which can mean more nails and debris in your yard, and they have higher waste disposal costs.
However, starting from scratch will help you identify and repair rot, water damage and termite damage.