Quote:
Originally Posted by SailinAway
Two sides of the roof face south and east, where there won't be any wind-driven rain. One short side faces west, which I guess would be exposed to wind-driven rain. There has never been an ice dam on this roof. It's easily reached with a roof rake or shoveled clean from the roof.
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Ice dams typically do not form on porch roofs over unconditioned (or open) space. They occur when there is too much heat leakage from below, such as by direct thermal conduction through framing, leaks into the attic from wiring penetrations, around pull-down attic stairs, and can lights in the ceiling. Melt water on the roof surface runs down to the overhang and gutter area, where it refreezes, forming the ice dam and backing up melt water. That is why current code requires a waterproof covering, such as Grace Ice & Water Shield, from the edge of the roof going back to a point above two feet inside the exterior wall below.
If you have a sloping intersection between roof and exterior wall of the house, be sure the roofer installs kickout flashing at the lower end, to divert rainwater out and away from the siding. Below is one many diagrams and photos showing different types of kickout flashings; google on that for all sorts of information on the subject.
