But here in the Midwest, ice damming happens without much warning, and can cause significant damage to the inside and the outside of your home.
Ice dams are caused when warm attic air melts some of the snow on the roof; the water runs down to the roof overhang and refreezes. The cycle repeats until a "dam" of ice has built up on the roof overhang.
The dam, and large icicles that often form with it - can get heavy enough to damage the roof - even pulling off gutters and downspouts.
More critically, the ice dam blocks the drainage of additional snow-melt from the roof, allowing water to back up under the shingles. That water can wick up under the shingles and leak into the house, damaging insulation, framing, drywall, and trim.
So how do you prevent this snow-belt menace?
There are technical solutions - the right amounts of attic insulation and ventilation are the most important - but like most everything we talk about at SoP, proper design and detailing keeps ice-damming out of your life forever.
Typical "production" house roof detailing has two critical flaws that actually contribute to ice-damming. Both are the result of cutting corners to cut costs (this is potentially a very expensive place to be cutting costs).
The first flaw is "pinching" the attic insulation out near the walls, where the roof slopes down all the way to the attic floor. If the insulation's too thin at this point, it won't have the necessary R-value you need to prevent the air in the attic from warming up and melting snow on the roof.
Solve this problem - permanently - by using a "raised heel" detail at the roof edge, and get the full depth of insulation at the most critical point.
Yeah, this raises the roof a little; you'll spend a bit more on siding and trim - but what was it your grandparents told you about an ounce of prevention?
|A deep overhang helps prevent ice-damming|
You're better off to extend the overhangs as far as stylistically and structurally possible. For some home styles that could mean three or four-foot overhangs (and never any ice-damming).
But for most homes, a full 16 inches of overhang from the outside wall is probably enough, assuming the insulation and ventilation are right for your climate.
Roof details are a bit technical, but they're also an important feature of a home's design. Protect your house from winter weather damage by getting the details and the design right.