When the time comes to reroof a building with an existing asphalt shingle roof, a decision must be made whether to remove the old shingles or apply new shingles on top of the existing layer. Most building codes define the options as follows:
Reroofing: The process of recovering or replacing an existing roof covering.
Roof Replacement: The process of removing the existing roof covering, repairing any damaged substrate, and installing a new roof covering.
Roof Recover: The process of installing an additional roof covering on an existing 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.
In some cases, local building codes will limit the available options. Generally, most do not allow more than two roof coverings on a building. In many cases, it is not necessary to tear off old
shingles before installing new shingles. However, in some cases, conditions necessitate roof replacement. The benefits of replacement include having the opportunity to inspect the roof
deck, repair any damage, and improve deck attachment to the underlying structure.
Each roof must be evaluated individually. General guidelines can facilitate an informed decision on whether to replace or recover an existing asphalt shingle roof. Note: some asphalt shingle designs do not lend themselves to recovering. For example, most manufacturers do not recommend installing new shingles over existing laminated shingles. Consult the shingle manufacturer for specific recommendations. These guidelines include but are not limited to the following:
- Confirm that local building codes permit the installation of an additional layer of shingles.
- Make sure the structure beneath the roof deck has sufficient capacity to bear the weight of another layer of shingles.
- Ensure the roof deck remains structurally sound and allows for adequate fastener retention.
If a roof has only one layer of shingles that lies flat and the deck is in good condition, replacement may not be necessary. Not only will the existing layer provide a secondary backup roof for the new shingles, but it will also save the cost and inconvenience of removing and recycling or disposing of the old shingles.
If any of the following is true, the existing shingles will likely need to be removed:
- The existing roof has two layers of shingles. Note: local building codes may define the number of permissible layers.
- The roof structure shows signs of sagging across the ridge or truss lines. If the roof does not look straight and does not feel solid, have the structure inspected by a licensed structural engineer to check for structural defects.
- An inspection of the roof deck reveals rotted or warped wood or large gaps (greater than ¼ inch) between the deck boards. Rotten, warped, or otherwise damaged boards must be replaced before applying new shingles. Note: for best roof performance, consider re-decking “board” (wood plank) roof decks with a layer of code compliant sheathing before installing new shingles.
- The existing shingles are so uneven and distorted that it would not be either possible or practical to flatten all raised areas enough for the new roof to lie flat.
Additional considerations include:
- This reroofing process should include an evaluation to determine that the existing attic ventilation is adequate. See ARMA Technical Bulletins “Considerations in Attic Ventilation” and “Why Ventilation is Important.”
- Removal of a previously installed ice dam protection membrane may be challenging during a roof replacement. See ARMA Technical Bulletin “Self-Adhering Underlayment Removal Prior to Steep Slope Re-Roofing.”
- Impact resistance ratings for asphalt shingles may be affected when new shingles are installed over existing shingles.
- Many factors may affect whether a roof covering should be replaced or recovered. It is important to discuss the options with your roofing professional. Your decision can impact not only the curb appeal of your home but also 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.
Nothing contained herein shall be interpreted as a warranty by ARMA, either express or implied, including but not limited to the implied warranties of merchantability, fitness for a particular purpose or non-infringement. IN NO EVENT SHALL ARMA BE LIABLE FOR ANY DAMAGES WHATSOEVER, including special, indirect, consequential or incidental damages or damages for loss of profits, revenue, use or data, whether claimed in contract, tort or otherwise. Where exclusion of implied warranties is not allowed, ARMA’s liability shall be limited to the minimum scope and period permitted by law.
