We had over 10 feet of snow this winter in central Vermont and relatively mild winters. The result was many homes had bad ice dams on the roofs. These occur as heat from the attic is transferred to the roof deck. There the snow acts as insulation to create the perfect environment for melting. As the melt water moves to the overhang or drip edge of the roof it refreezes because there is less heat. The ice can easily build up to a layer that is a foot or more thick. The melt water then backs up behind it causing ponding that can back up past the shingles and run into the attic and walls. Of course the more heat loss into the attic, due to reduced or ineffective insulation or air leakage, the worse the problem will be.

 

The damage to the roof and building can be substantial. Once the water penetrates the envelop, it remains for weeks, months or "forever" as it has little potential to dry out. You can see on the attached images the brown stains on the exterior siding. The staining is a clear indicator that the water passed through the wall. The thermal image, taken early in the morning when temperatures were right at freezing, shows a mottled pattern below the window and warm (wet) studs elsewhere. Based on these images a contractor will open up several of the walls for further investigation—I have little doubt it remediation will require substantial removal of existing wall insulation. The danger of not doing the job correctly, of course, is that the wall cavities could quickly become the perfect environment for mold growth.

 

So, while the snow in Vermont has finally melted, the damage done to some buildings remains.

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Thermally Yours,

John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820