There are three ways to defend against the damage ice dams cause Insulation, Ventilation, and Waterproofing underlayment. All three work together. Insulation keeps heat from escaping from your home’s living space into your attic. Ventilation removes the heat and helps keep the roof deck evenly cool to help prevent snow from melting on the roof. Finally, Waterproofing shingle underlayment is laid across the roof before roof shingles are applied.
Ice & water barrier is a critical last line of defense against leaks, preventing backed up water from getting into your home wherever it is applied.
Here is the ICC code statement;
In areas where there has been a history of ice forming along the eaves causing a backup of water as designated in Table R301.2.(1), an ice barrier shall be installed for asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate, and slate-type shingles, wood shingles and wood shakes. The ice barrier shall consist of not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet shall be used in place of normal underlayment and extend from the lowest edges of all roof surfaces to a point not less than 24 inches (610mm) inside the exterior wall line of the building. On roofs with slope equal to or greater than 8 units vertical in 12 units horizontal, the ice barrier shall also be applied not less than 36 inches (914 mm) measured along the roof slope from the eave edge of the building.
So with re-roofing or new roof construction,1 or 2 rolls of Ice barrier must be installed on eaves depending on the eave overhang length, and all in areas where roof pitches change, in valleys and around the roof openings like chimneys and skylights.
This code will not be applied to the unheated/ detached structures.
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