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Ice Dams: Take Preventive Steps NOW



We had our first dusting of snow here in Boston this week — always a sharp reminder of what’s to come.  And if your home is one of the many that develops ice dams along the eaves, you still have time to do something about it!



Ice dams form when heat from your house rises into the attic and melts snow on the roofs.  When the water runs down the roof and reaches the cold eaves, it freezes.  Now you have a dam.  As more snow melts above the dam, the water pools and gets into the house.  Obviously, that’s not a good thing!  The result: peeling paint, warped floors, stained ceilings, and wet insulation in your attic that is dramatically losing R-value.



In principle, stopping ice dams is easy: all you need to do is keep the entire roof at the same temperature as the eaves (i.e. close to the outside temperature).  Accomplishing that means VENTILATE. INSULATE. BLOCK AIR LEAKS.  Here are a few details to help you prevent damage to your house and the need to file insurance claims!



A ridge vent coupled with continuous soffit vents will circulate cold air under the entire roof.  According to information published by This Old House, both the ridge and soffit vents should have the same size openings and provide at least 1 square foot of opening for every 300 square feet of attic floor.



Adequate insulation on the attic floor is meant to keep your attic cold in the winter and keep heat in the house where it belongs.  An article published by U.Mass-Amherst in 2011 cited that houses in the northern U.S. should be equipped with ceiling insulation of at least R-38. (about 12 inches of fiberglass or cellulose)


Block Air Leaks

If you have an unsealed attic access door or a whole house fan, you have major openings for heat to rise from the house into the attic.  You should cover them with weather-stripped caps made from foil-faced foam board.

Make sure any exhaust vents (kitchen, bath, dryer, etc.) lead outside through the wall or the room, never through the soffit.  Remember, you’re trying to keep the soffit the same temperature as the outside.

Replace any old-style recessed lighting. (Significant heat radiates from them and they can’t be insulated without creating fire hazards.) Use sealed “IC” (Insulated Ceiling) fixtures that you can cover with insulation.

Flash around your chimney with L-shaped steel flashing held in place with unbroken beads of a fire-stop sealant.

Seal and insulate ducts: You should spread fiber-reinforced mastic on the joints of HVAC ducts and exhaust ducts.  Cover them entirely with R-5 or R-6 foil-faced fiberglass.



If you haven’t been able to take these preventive measures, here are a couple of action steps you should take:


Before any snow falls, make sure you clean your gutters of all leaves and debris that can block water from flowing freely. (Not comfortable on ladders; hire a local handyman.)

Get a roof rake.  Then you can CAREFULLY remove snow right after a snowfall at the edges of eaves and minimize the severity of the dams. 

If you develop ice dams, fill the leg of a discarded pair of pantyhose with sodium chloride ice melter. Place it across the ice dam and overhang the gutter.  You want to melt the dam there and create a channel for the water to flow into the gutter and off the roof.

Important caution: don’t try to break up the dam with a hammer, ice pick, shovel, or anything like that.  It’s dangerous for you and it’s highly likely you’ll damage your roof.


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