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Homeowner Tip: Ice Dams — What They Are & How to Prevent Them

The following information comes from Colin Gibson of Gibson Home Improvement — I thought it was very good information and appropriate for our current weather, so got his permission to share…

ICE DAMS — by Colin Gibson

I’m writing because this time of year, I spend a lot of time on roofs. I get called in to remove a lot of ice dams, and to fix the problems that they cause. I see lots of good people, guided by the best of intentions, try to fix the problem, only to end up wasting time and money – and sometimes making the problem worse, without meaning to.

I don’t claim to have all the answers. If you look on the Internet, you’ll see five different solutions, some contradictory. All I can say is, after doing this for close to 20 years, I’ve developed my own ideas on what works, and what doesn’t. Here are a few basic principles I adhere to.


What causes ice dams? It’s heat, escaping the warm confines of the house. “Keep a cold attic,” is one of the truest expressions in home management. Heat escaping the house into the attic (through poor insulation, or bathroom or kitchen vents, or recessed lights) goes up to the roof. The heat melts the snow, which then freezes, becoming ice. More snow melts (or rain comes) – when the water hits the ice, it backs up underneath the roof shingles, and comes into the house.

Ice Dams


The first key to a cold attic is good air flow. The most important air flow is from the soffits to the ridge vent (along the rafters). I have come to firmly believe that EVERY house should have soffit vents (strips cut into the bottom of the eaves) and a ridge vent (a strip cut along the peak of the roof). And, please, don’t be tempted to install those circular soffit vents. They don’t provide the air flow that soffit strips do, and they just fall out over time. A well-ventilated attic reduces the chance of mold, too. If you see white spots on the underside of your roof boards, or on the rafters – or worse, ugly bad black mold– you’ve probably got a problem you should address.

Ice Dam Damage


The other key to a cold attic is keeping the heat in the house. You should have at least R-38 (about 10” thick) on your attic floor. More never hurts. Also, block the sources of typical heat leaks – that’s most often bathroom and kitchen vents, or recessed lights. You can spray insulation around vent cavities, or use rigid or foam insulation around recessed light cans. (Depending on the rating of the lamp, you may to leave some space around the light to allow for the heat. Ask me if you have questions.)


All too often, I see over-zealous insulators hurriedly spread insulation over the soffits. I get it – no one wants to spend too much in an attic. But this defeats the purpose, blocking the air flow from the soffits! You can see the light through the soffits in the picture below, telling you that the insulation is good. Keep repeating to yourself – “Keep a cold attic.”

Proper Attic Insulation


Again, many are tempted to use the vents on either end of the attic. They’re not a bad thing. But they don’t promote the good air flow – from soffit to peak, keeping the roof cold (especially on the bottom three feet, where most ice dams occur).


The inexpensive heating cables at Lowe’s or Home Depot are tempting. But any experienced electrician will tell you, they replace them all the time, when they burn out quickly. We do install systems that go on automatically, when they sense moisture, below a certain temperature. They are more expensive, but don’t burn out, and you don’t have to worry about turning them on and off.


I see lots of ice dams on houses without gutters. The only difference is, I see basement flooding or mold and rot, because water flows off the roof onto the foundation, or the house. In my experience, gutters don’t dam up – unless they are blocked, or they are sloped backwards, so you have sitting water. The ice dams start with the hot attic.


No matter what you do, it’s still a good idea to clear the first three feet of roof (where the ice dams occur). Valleys (where two roof angles come together) are also a trouble spot. Keep a roof rake handy – or call me.

If you do tackle the ice dams by hand, be careful. It’s stating the obvious, but worth saying. Set the ladder securely in the snow, and clear any ice from the rungs. And even if the roof looks walkable, stay off. You don’t know when you’ll hit a slick spot, or the snow will give way. And use care when freeing the ice dams. Hammers can break the ice, but they also puncture the asphalt shingles. And the shingles can stick to the ice, and tear up when the ice dam comes free. It’s a delicate, painstaking process.

Contributed by Colin Gibson, Gibson Home Improvement — 617-678-6789 — thanks, Colin!


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