Self-adhering underlayment is generally applied to the roof deck on the eaves, rakes, and valley areas of steep slope roofs and as flashing around roof penetrations. Self-adhering underlayments are installed on critical areas of the roof to minimize the likelihood of water penetrating the roofing system. In order for self-adhering underlayment to perform well, it must adhere firmly to the roof deck. As a result, it can be difficult to remove without damaging the deck material.
Removal of self-adhering underlayment is always recommended in situations in which it can be removed without damaging the deck. Removal will facilitate examination of the deck for deterioration and damage, reduce build-up of material that could interfere with proper drainage, and eliminate unevenness that may create an aesthetic issue with the newly installed roof covering. Removal of self-adhering underlayment becomes more important when more than one layer of self-adhering underlayment is present.
If only one layer of self-adhering underlayment is in place, and it is not possible to remove it without damaging the deck, installation of a second layer of underlayment over the existing membrane may be permissible: Check with the underlayment manufacturer’s installation instructions and local building codes for details. Offset end and side laps in the new and existing underlayment to minimize thickness build-up, and “feather in” the new underlayment by extending the new material a minimum of 8” up the slope onto the bare deck. This will reduce the likelihood of problems with drainage and aesthetics.
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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