Another advantage of asphalt shingles is normally a second layer that can be applied after the first has worn out. A common practice of installing a third layer to save expense by homeowners and roofers is often undertaken. This usually is a problem because it puts too much weight on the roof, shingles wear rapidly and the roof surface becomes uneven and is prone to wind damage. Asphalt shingles are sometimes improperly installed over old wood shingled roofs and sometimes even old slate roofs.
Asphalt Shingle Slate Wood Shingle Asphalt Rolled Tile
