After the big snowfall in Minnesota last night, it's a good time to talk about ice dams. Ice dams are caused by the same thing I've been blogging about for the last several entries; heat loss! The most obvious sign of heat loss in attics is ice dams - those huge masses of ice that build up at the edges of roofs. Ice dams occur because heat from the house escapes in to the attic, warms the roof, and causes snow to melt. When the water gets to the cold overhang at the eave, it freezes. As the ice builds up, it literally creates a dam. The trapped water can then leak into the home and cause damage to the roof decking, structural members, insulation, and even stain the ceiling.
To prevent ice dams from occurring, you need to stop the heat loss. The best way to do this is to seal attic bypasses - you can read more about this in three of my recent blogs - Frost in Attics, Inspecting Insulation, and Photos of Attic Bypasses. The other two ways to help prevent ice dams are by having adequate insulation and ventilation. Insulation will obviously help to prevent heat loss, and proper ventilation will help to keep the roof colder; the colder the roof, the less chance for the snow to melt in the first place.
Older one-and-a-half story houses are especially susceptible to ice dams because there is usually very little access to all of the attic spaces that need attention. If this is the case, there are still some steps you can take to control the damage caused by ice dams. The least expensive and most labor-intensive way to prevent ice dams is to remove the snow from the eaves using a roof rake. It's best to remove the snow right away, when it's light and fluffy. The longer you wait, the more ice will accumulate. If you can remove the snow down to the shingles, the sun will usually keep the shingles warm enough to prevent ice from forming at the eaves.
If you're looking for a less labor-intensive method of preventing ice dams, you could install heat cables at the eaves. These will usually prevent ice dams from forming, but electric heat cables are expensive and use a fair amount of electricity to operate, making them an environmentally UN-friendly solution. Even manufacturers of heat cables state that they are not the most efficient way to solve ice problems.
The worst way of dealing with ice dams is to get on a ladder and hack away at your ice dams with a hatchet or ice pick. This is dangerous, and you could cause damage to your roof. I've seen many roofs with big hatchet marks in the shingles from people chopping too deep. I don't recommend doing this.
The bottom line? If you can't stop your ice dams the right way, buy a roof rake.
Reuben Saltzman, Structure Tech Home Inspections