Self-Adhering Underlayment Removal Prior to Steep Slope Re-Roofing

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.
Removing self-adhering underlayments is always recommended in situations where it can be
removed without damaging the deck. Removal will facilitate examination of the deck for
deterioration and damage, reduce buildup 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, check with the underlayment manufacturer’s installation
instructions and local building codes to determine if installation of a second layer of
underlayment is permissible. If a second layer is permitted, offset end and side laps in the new
and existing underlayment to minimize thickness buildup 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.
If two or more layers of self-adhering underlayment are in place, all layers should be removed.
If removal of the existing material cannot be accomplished without damaging the deck, then
the roofing contractor may have to remove and replace the decking in the areas covered with
self-adhering underlayment.