The Ice Dam Cometh - Smart Inspector Science
By Tom Feiza, Mr. Fix-It, Inc., HowToOperateYourHome.com
During a winter inspection, you notice an ice dam—a thick, solid ridge of ice that built up along the eaves. Should you report it as a visual defect? What causes this, and what does it mean to the buyer?
Yes, report it.
You should report a visible ice dam and recommend further investigation. In one case (Photo 1), I noted possible damage to gutters and roofing. Ice dams can cause water damage to overhangs as well as inside the home.
You’ll see a heavy buildup of ice at the cold edge of the roof (Photo 2). The snow in back of the ice dam has melted, so it looks thinner. This area of thin snow is just above the interior wall of the home.
What causes ice dams?
The simple answer: heat. Heat builds up in an attic and melts snow on the roof (Illustration R002). The snow-melt/slush slides to the edge of the cold overhang, where it re-freezes and creates a dam along the roof’s edge. When more snow-melt occurs above the ice dam, water builds up and can leak into the structure of the home. Asphalt shingles are not designed to be buried in water—they will leak.
A warm attic is at the bottom of this.
Certainly, lack of insulation and ventilation allow an attic to get too warm. Then trace this process back one step and you’ll likely find air leaks from the heated envelope into the attic.
Air leaks? Really?
Yes. In my typical investigation of interior leaks due to ice dams, I often find a significant air leak near the ice dam. I found one ice dam caused by lack of air sealing around a masonry chimney. There was a 6-inch opening around the chimney that led all the way down to the basement.
In another case, a new home addition with great insulation and ventilation was experiencing ice dams. The remodeling project included installation of two ceiling can lights over a built-in window seat. Warm air was leaking around the ceiling lights (Illustration R021). These insulated contact (IC) -rated fixtures created excessive heat in the small attic area over the window. The rest of the attic had no ice dams. Although an IC rating means it’s safe for insulation to directly contact the light fixture, that doesn’t mean it’s airtight. If the housing has holes in it, air can leak in.
What you must do
Report ice dams and recommend further evaluation. You must also report lack of ventilation and improper insulation. Also, keep an eye out for can lights and air gaps from the heated space beneath the dam.