When the time has come to re-shingle your roof, one decision you will be faced with is whether to strip off the old shingles, or apply the new ones right over the existing layer. There is no easy answer. Although each roof must be evaluated individually, there are some general guidelines you can follow to help you make an informed decision.
You will probably have to tear off the existing shingles:
In some cases, it is not necessary to tear off the old shingles before applying the new ones; if your roof has only one layer of shingles, laying flat, and the deck is in good condition, a tear-off is not needed. Not only will the existing layer (although old and weathered) provide a secondary back-up roof for the new shingles, but it will also save you the cost and inconvenience of removing and disposing of the old shingles. However, it is suggested that before making a final decision, a verification be made with local building officials to ensure that you do not infringe on any building code. As well, consideration should be given to the shape/dimension of both the old and new shingles, as some combinations may telegraph the old layer through the new layer.
Even though shingles are not environmentally hazardous, unnecessarily dumping into landfills is a disservice to the community. Currently many companies are researching ways to recycle roofing tear-off material into other products. The next time your roof needs replacing, it is possible that technology will exist to more readily recycle those shingles, rather than throw them away.
The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA.