When the time comes to reroof an existing asphalt shingle roof, a decision must be made whether to remove the old shingles or apply new shingles directly over the existing layer. Most building codes define the options as follows:
Reroofing: The process of recovering or replacing an existing roof covering.
Roof Recover: The process of installing an additional roof covering over a prepared existing roof covering without removing the existing roof covering.
Roof Replacement: The process of removing the existing roof covering, repairing any damaged substrate and installing a new roof covering.
In some cases, local building codes will limit the available options—most do not allow more than two roof coverings on a building. However, there is no easy, universal answer if only one roof is in place. Although in many cases it is not necessary to tear off old shingles before installing new shingles, some roofing professionals will insist on replacement because it ensures that a completely new roofing system is installed.
Although each roof must be evaluated individually, general guidelines can help make an informed decision whether to replace or recover an existing asphalt shingle roof.
• If a roof has only one layer of shingles that lay flat and the decking is in good condition, a tear-off may not be needed. Not only will the existing layer provide a secondary back-up roof for the new shingles, but it will also save the cost and inconvenience of removing and disposing or recycling the old shingles.
• Before making a final decision to tear off or recover, check that local building codes are being followed.
• Adequate roof ventilation should be provided (See ARMA Technical Bulletin, “Ventilation and Moisture Control for Residential Roofing” for additional details and information).
The existing shingles will probably have to be removed if:
• An inspection of the roof deck reveals rotted or warped wood or large gaps between the deck boards. Any rotten or damaged boards must be replaced before applying new shingles. [Note: for best roof performance, consider re-decking “board” roof decks with a layer of APA (The Engineered Wood Association) Grade ½” plywood before installing new shingles.]
• There are more than two layers of existing shingles on the roof. Note that the local building codes may require removal of more than one layer.
• The roof structure shows signs of sagging across the ridge or truss lines. If the roof does not look straight and feel solid, have the structure inspected by a licensed structural engineer to check for structural defects.
• The condition of the existing shingles is so uneven and distorted that it would not be practical to flatten all raised areas enough for the new roof to lay flat.
Many factors may play into whether a roof can be recovered or replaced, so it is important to discuss the options with your roofing professional. Your decision can impact the curb appeal of your home and the performance of your roof.
*DISCLAIMER OF LIABILITY: This document was prepared by the Asphalt Roofing Manufacturers Association and is disseminated for informational purposes only. Nothing contained herein is intended to revoke or change the requirements or specifications of the individual roofing material manufacturers or local, state and federal building officials that have jurisdiction in your area. Any question, or inquiry, as to the requirements or specifications of a manufacturer, should be directed to the roofing manufacturer concerned. THE USER IS RESPONSIBLE FOR ASSURING COMPLIANCE WITH ALL APPLICABLE LAWS AND REGULATIONS.
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