I touched on insulation and air-sealing in a few recent posts. And as happens in the winter, we’ve noticed a big increase in the last few weeks on people asking about icicles and ice damming. It’s probably time for a quick refresh and retread of an earlier post.
What is Ice Damming?
Big icicles and ice dams are typically caused by poor or missing insulation and air leakage from your house into your attic. In the winter, this warms the roof and causes the snow to melt. The melting snow then moves down the roof slope until it reaches the cold overhang, where it refreezes.
The process forms icicles and can actually create a dam that eventually forces the water to back up under the shingles and sometimes into the ceiling or wall inside the home. In addition to roof and water damage, ice dams can cause structural decay and mold and mildew to form in attics and on wall surfaces.
Big icicles themselves, like those shown here, are obvious signs that you’re at risk.
But snow melt patterns can also indicate a problem of too much heat loss. In this photo below, you can see snow melting off the roof at different rates, driven by heat loss from the house.
Uneven snow melt also is a sign that something is awry
And in the townhouse complex below you can see the building that GreenHomes treated with even snow still on the roof—a sign the building isn’t losing energy rapidly. Conversely, you see the untreated building with the snow melted–a sign that it’s losing a lot of energy. No big icicles this time—but had it been a bit colder, the melting snow would have refrozen at the eaves and created big problems.
- The townhome treated by GreenHomes loses heat more slowly through the attic and thus snow melts slowly and doesn’t accumulate as ice out at the eaves.
This town home has not been treated and the wasted heat melts snow quickly. In the right temperatures, the melted snow would refreeze and create ice problems--bad news. And in any event, this folks in this building are spending a lot more on energy than they should.
Fortunately, you can dramatically reduce damage from ice damming by sealing the holes connecting your heated living space and the attic, as well as properly insulating your attic. There are different techniques to stop air leaking through recessed lights, leaky heating ducts, attic access doors, and plumbing and electrical penetrations. Sealing these leaks keeps warm air in your house were it belongs. Together, with adequate levels of insulation, this greatly reduces the chance of ice damming and large icicles. You do NOT just want to add more insulation before sealing the air leaks—this can actually create additional problems that can also damage your roof.
It’s important to not that you can’t eliminate icicles completely. Small icicles are normal. And some roof architecture–especially big valleys draining to a small corner–are especially challenging. But if you have long icicles or thick heavy ice you should act quickly to prevent damage. (And this means preventing the ice from forming in the first place, not risk life, limb, and your roof trying to chip off ice that’s there.)
Do it right. Find the important leakage points and seal them up. Then add a lot of insulation. And afterwards, as with any time you change the way your house works, have your combustion appliances tested to make sure they’re operating safely and efficiently.
An added benefit to this, of course, is you’ll save energy, save money, and be more comfortable in your home, too!
Save the ice for your holiday cocktails!
[Update, see more roof melt and icicle photos.]
P.S. The added insulation can qualify for the $1,500 federal credit. Save money while you save you roof!