- The cushioning effect of the olf roof under the new alloes impacts from branches, hail and even hard rain to dent the new shingles
- Any curled shingles or other flawswill show through to the new shingles.
- When completed, there are usually telltale signs of the previous roof, such as cureled shingles at the edge.
- There is a limit to the number of layers- the wtight of the roof- a house can bear.
- The maximum number of layers may be mandated by local building codes.

Inspect you roof thoroughly. If you find signs of leaking such as moisture, stains, delaminating or separating plywood and rot, it is imperative that you remove the existing rood and repair the framing. Ice dams or splashing from gutters often causes rot at the eaves. You can carefully strip off the first two or three courses of shingles, cut out the damage, and replace the removed shingles with similar new ones. This will give you an even surface for reroofing, but may take as much time and effort as stripping the whole roof which would provide a better surface.