For much of the U.S., the possibility of ice dams forming along
steep-slope roofs' eaves is enough to require an ice-dam protection
membrane in addition to any other roof underlayment local building
codes may require. In such cases, NRCA recommends using a self-adhering
polymer-modified bitumen sheet underlayment.
In areas where ice-dam protection is required (based on
temperature, history and/or local building codes), an ice-dam
protection membrane should extend from an eave's edge to a point 24
inches inside the interior face of a building's exterior wall.
Roofing and Waterproofing Manual, Fifth Edition recommends
extending an ice-dam protection membrane 24 inches beyond the
interior face of a building's exterior wall if a roof's slope is
greater than or equal to 4-in-12 (18 degrees). If a roof's slope is
less than 4-in-12 (18 degrees), the ice-dam protection membrane
should extend 36 inches beyond the exterior wall.
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