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A Bunch of B.S.* (*Building Science, of course)

A Thermal Image Walk-Around

Nate Gusakov

Recently we were called to perform an envelope assessment for a house under partial renovation in Starksboro, VT. After some interior demolition work, the builders had noticed squirrel damage to the insulation in the wall cavities they had exposed. They subsequently asked us to do a thermal imaging inspection of the house to make sure there wasn’t further damage lurking unseen behind walls that weren’t going to be renovated. It was a fairly simple process to walk around the house taking pictures with the thermal imaging camera. The amount of information gleaned from this simple walk-around is amazing. Here’s just some of what we learned:

Images 1-A & B: Thermal and visual images of the west wall from the inside. Courtesy images.

Image 1-B

Squirrels, you say? Squirrels, indeed. Take a look at image 1a. There is a painfully obvious thermal signature where the tree rats entered the top of the wall at the eave, tunneled their way back and forth down through the insulation between the studs, and fully excavated a cozy nest in the middle of the wall. Sigh! At least we know it’s there, and now the builders can take care of it.

Image 2 A & B: Thermal image of the east side of the building with a visual image inset. Photos courtesy of Zone 6 Energy.

Image 2-B

Now take a look at image 2, which shows the east side of the house from the exterior. Above the foundation in the thermal image, there is a relatively smooth color scheme across the exterior wall of the building. This indicates that the insulation is undisturbed here—there are gentle gradations of orange and yellow, but no distinctly contrasting colors. Then, take a look at the foundation wall below the clapboards. To the human eye, it looks like one undisturbed stretch of grey concrete. To the thermal camera, however, another story is told in very clear terms!

The left side of the foundation wall is deep purple, showing that it is at least as cold as the snow. Halfway along the wall, the foundation suddenly changes to bright yellow and white, indicating a starkly different surface temperature, warmer even than the wall above it. What is happening here? In the south end of the basement (left side of the picture) the concrete walls are well-insulated on the interior, so heat from inside is kept inside. The north end of the basement is uninsulated bare concrete on the interior, so the wall there absorbs heat from the inside of the house, conducts it (very well, at that) across its mass, and radiates that heat to the outside, 24/7. To the thermal camera, it glows. To the homeowner, it costs money.

The thermal image walk-around is deceptively simple. It would take dozens of pages, however, to begin to fully unpack the amount of information that is gleaned about the building envelope. In this case, the value to the builders (and homeowners) is real and significant: Squirrel damage can be addressed on a case-by-case basis instead of tearing apart whole walls to investigate, and the rest of the renovation can proceed with confidence that a complete and functional thermal envelope will be the result.

Nate Gusakov is a building envelope consultant and AeroBarrier installer for Zone 6 Energy.

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