How far should an ice-dam protection membrane extend from the inside to the exterior wall on slopes less than 18 degrees?

The requirement for an ice-dam protection membrane to extend a certain distance from the inside to the exterior wall on roof slopes less than 18 degrees is crucial for preventing water damage caused by ice accumulation. The correct extension of the membrane is 36 inches. This dimension is critical as it ensures that the area most susceptible to ice dam formation is adequately protected from potential leaks that can occur when melting ice backs up under the shingles and seeps into the roofing structure.

This 36-inch requirement is a standard in many building codes, as it effectively covers the eaves and valleys where ice dams are most likely to form. An insufficient extension could leave areas exposed to moisture intrusion, which can lead to significant structural damage, mold development, and costly repairs. Thus, adhering to the specified measurement provides a safeguard against these risks by ensuring that the membrane provides sufficient coverage to mitigate ice dam effects.