How to Treat and Prevent Ice Dams | Ask This Old House

Ask This Old House general contractor Tom Silva explains the best ways to keep your roof and gutters free from those dreaded ice dams. (See below for a shopping list and steps.)

Tom talks to Kevin about ice dams and the best ways to prevent them.

Tom offers some temporary solutions, like placing some ice melt or rock salt in an old sock and tossing it onto the ice dam, allowing a channel for the water to drain.

More permanent solutions include increasing insulation in your attic or your roof. Some insulations, like fiberglass bats, can be purchased from a home center. Others, like expanding spray foam, require professional installation. An insulation contractor can make specific recommendations for your home.

Shopping List for How to Treat and Prevent Ice Dams:
- Ice melt or rock salt
- Additional insulation

Steps for How to Treat and Prevent Ice Dams:
1. To fight existing ice dams, try placing ice melt or rock salt in an old sock or a paper bag and toss it onto the dam, allowing for drainage.
2. To prevent future ice dams, look to increase insulation in attics and/or roof rafters.

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How to Treat and Prevent Ice Dams | Ask This Old House

[rjwalker]

Another tip is to get a roof rake, and rake the snow off your roof right after a heavy snowfall, before it melts. With less snow on the roof, there will be less that melts and thus less ice dams.

[markoshun]

In many cases it isn’t caused by lack of insulation or heat loss from interior.
Often only part of the roof gets sun, so snow melts down and freezes up on the shaded edges making the dams, especially in the valleys where there’s 2 meeting rooflines.

[inTruthbyGrace]

Just remember to attach a string to that sock to BOTH reposition the sock when you have bad aim for your first 5 attempts to position that sock-o-salt.. (like me) AND so you don't end up needing to climb up a ladder retrieve socks off your roof or out of your gutter in the spring!!! :)

[tbischof]

Having adequate VENTILATION is also SUPER important along with enough insulation.

[joeseatat]

You are a lifesaver!! We were panicking, thinking we had holes in our recently redone roof. Who are we going to call? What are we going to do? Now we know we need to hire someone to insulate and we know a safe way to break up our dams until spring. Thank you!

[joegellman]

First step is to seal all air gaps between the house (conditioned space) and the attic (unconditioned space) under existing insulation. Can spray foam (or combine with rigid foam) all gaps, penetrations of wires, pipes, holes, recessed light cans, around chimneys, etc. Then reposition and add required insulation allowing for proper ventilation. Spray foaming rafters only makes sense if you want the attic to become conditioned space.

[ruthgodfrey]

I use an extendable swimming pool brush, large oval brush head. Pulls the snow off great.

[glennwilck]

Keep your roof edges clean and free of ice from the start it only gets worse the longer its left untreated. When you get a day above freezing that is the day to get the ice off and reset the dams to zero. Its called maintenance and is a must or bad things will happen!

[timrowlett]

Venting and air flow was not discussed and is very important. Getting warm air out of your attic is vital to preventing ice dams and keeping the underside of the roof deck cool.

[backpackingonline]

Insulate the attic floor, have a roof ridge vent cut and have clear soffits, or better, have drip edge vents to have a cold roof.

[MichelJosephCardin]

That yellow siding home that has an ice dam in the video at time of 0:17; is likely that has a washroom in that area or the range hood hose has an escaping amount of air and if someone bakes and what not or doesn’t use their range hood exhaust fan while their boiling of their spaghetti or such and if it is during a time of outdoor temperature that is close to freezing point; then if forced air furnace will become nonfunctioning because of the thermostat being warmed up by the cooking and snow will melt and freeze when it gets to the facia because heat rises and the soffit and facia is getting a flow of outdoor air as the circulation occurs between the insulation stops and the roofing materials and that is usually approximately 30 or so inches of cardboard along the center of 2/4 between the trusses which leaves an inch and a half of quick outdoor temperature air flow. And that is why you can see that there is an inconsistency of activity; there seems to be an area where heat was occurring between two rows of trusses. Well anyways; ventilation fixes everything. It might be a washroom also and that it may had been habit that after showers; door would become closed and would cool down slowly through the ceiling and maybe the fan is there also and vapour barriers should be sealed with the fan boxes also. But my money is on it being the kitchen with upper cupboards being all along our left of the window and sink at window with a void of cupboards over the sink or maybe halogen light inserts or halogen light fixture. I’m pretty sure that there was more heat right there. In the middle. Lol. I must have a lot of time on my hands right? Lol. Cheers. All they need there is correctly install the insulation and vapour barrier at the switching of constructing elements of the overhead structure where to the left of the door at the top would have a transitioning of sorts that attic changes either in having inner walls in the attic that turns the corner and maybe has been insulated too high between the studs where the blow in insulation should be level with the attic’s walls ones. I’m done here and they just need to unclog the airways through from soffit through to vents and add a vent if needed. Gooodd bye.

[mattlennon]

Insulation is great to "help" prevent ice dams. Ice dams are also caused when there is a thaw or sunny day in the winter which will melt the snow on the roof. It is not always heat loss from lack of insulation. All it takes is a snowy roof that currently has no melting snow to be hit by the warm sun on an above freezing day or two. This will cause large ice dams in no time at all. No matter what is done, in the right conditions ice dams are a fact of life where it snows.

[amandaluchtel]

I have recently heard that spray foam off gases toxic fumes. Is there another option to insulate the roof side of a knee wall? Like thick foam board? Also, should there be a rigid grooved piece between the insulation and the roof to provide proper ventilation and airflow?

[Jacno]

i remember working for this scummy roofer for a week. Home owner said he gets real bad ice damming in the winters. The roofer just upsold him new gutters and took off. Also as I was roofing beside him, him and his worker did such a terrible job i felt guilty when he told us thanks. in my head i knew the only sides that aren't gonna blow off would be the ones i installed.

[dadsbus]

Guys you missed the boat a bit on this one. Insulation is very important, but ventilation is equally important. I live in the great white north and see houses every day that have lots of insulation but are still ice damming badly. As soon as we create proper ventilation the problem is solved. It's a 2 part repair with both parts being equally important. Good insulation and ventilation happy homeowner.

[thelorax]

I always heard that insulating under the roof will make the shingles get excessively hot in the summer and they will not last as long. Isn't it better to insulate the attic floor with more instead of the roof?

[johnwilkins]

What if we want to leave floor open but don’t want to pay for the spray foam? Can I do the spray foam myself? Or will just traditional insulation not be enough between the rafters?

[desmo]

Wow no mention of air channels / baffles from vented soffit upward, and insulation on floor or up along roofline doesn’t actually reach the sheathing. Creating that air gap makes for a better thermal break than insulation alone and seems to make a difference.

[Crusader]

You really need a ventilated air gap so the immediate underside of the roof surface is as cold as the snow on top. Then the melting will stop.

[ksloan]

The lower the pitch the more susceptible it is to ice damming if you’re in an area that gets heavy snowfall