Homeowners living in warmer regions may have never even heard of ice dams—thankfully so. For everyone else, ice dams are a brutal fact of life and something to consider when roofing your house.

This is especially important because ice dams are often pushed by roofing companies as another one of those “options you may want to have or else…” Since it is natural to be suspicious of roofing companies offering "options," the instinct is to turn it down.

But is this a wise choice?  Let's look at what can happen when an ice dam forms; whether you should purchase them; and a rough estimate of what they might cost.

How Ice Dams Ruin Your House

1. Snow Falls. First, of course, the snow falls. It doesn’t have to be giant snowpack, either. Snow in any quantity can result in an ice dam.
2. Snow Melts. After snow falls on a roof, it will eventually (we hope at least) start to melt. Snow on a roof can melt quite rapidly, due to its high exposure to the sun and also due to heat rising up through the house. Homes with poor insulation are more susceptible to ice dams, because more heat escapes through the roof.
3. Snowmelt Drains. The liquid snowmelt flows downward until it reaches the eaves or the gutter. But the eaves or gutter (we bring up both of these because you may not necessarily have a gutter, but all houses will have eaves) do not warm up like the upper regions of the roof do. The eaves and gutters remain quite cold, meaning that ice builds up. It becomes a cyclical process. The snowmelt flows down, reaches the ice, and turns into more ice.

1. Ice Dam Results. Eventually, you have a quite sizable dam of ice along the edges of your roof.
2. Water Seeps Between Shingles. So what's the big deal? The snowmelt is going to keep coming down and backing up behind the dam. Then, that backed-up water has the luxury of time to seep under the shingles. After the water seeps between the shingles, it flows into the ceiling and and into your house. Now that is a very big deal.

The problem is exacerbated if you have wood shake shingles, which do not hold back water as well as asphalt or composite shingles.

Making A Case For Installing Them

When roofing companies install ice dam protection, they run a strip of rubber flashing all around the perimeter of the roof before laying down the shingles.  This "rubber" is actually high density cross laminated polyethylene that is 36 inches tall (that is, from eaves toward peak of home's roof) and very long, about 75 feet or more long.

No, it does not prevent the ice dam. It merely helps to prevent the seepage from the ice dams that goes under your shingles from reaching and damaging the wood deck below the shingles.

Ice dams are quite a serious problem. Even if the water does not reach the stage of flowing through your ceiling and into your house, it will probably cause moisture in the attic which will then result in mold.

I recommend ice dam protection.  It must be done at the time of roofing; it cannot be done retroactively. 

How Much Should You Pay?

Materials (Grace Ice & Water Shield) run about $160 for 75 linear feet.  Two rolls for a total of about $320, tax not included, would cover a small home.  Presumably, the contractor would be purchasing his materials on wholesale, thus cheaper.  However, as a rule of thumb, figuring in the cost of labor might double the cost of materials.