Tearing off the old roof
When it comes time to replace your roof, you'll need to decide if you want to tear off the old roofing. A single layer of existing asphalt shingles in good condition can be roofed over once, but an existing second layer and other types of roofing materials must be removed before new roofing can be installed. Expect to pay $1 to $3 per square foot to tear off and dispose of old roofing, depending on the complexity and steepness of the roof.

While it may save money to add a second layer of roofing without the expense of tearing off the old shingles, keeping the existing roof means keeping the old flashings and vent boots -- generally considered the weak link in your roofing system. The new flashings and vent boots that accompany a clean installation ensure the best possible protection for your home and generally are worth the extra cost of a tear-off.