You don’t necessarily need a fog machine to find where your house is losing energy. A thermal imaging camera will do the job, and what it reveals might surprise you.
We recently ran an infrared scan of one of our own home’s interior ceiling and walls, and the images told a clear story: It was a combination of thermal bridging and cold air sneaking in right where it shouldn’t be, especially at the top and bottom plates of the exterior walls.
What the Thermal Images Revealed
One image showed a distinct temperature anomaly right where the ceiling meets the wall, the top plate. Another confirmed it: a dark, cold zone along that same junction, indicating cold outside air was infiltrating at the top plate. This is a classic sign of air leakage, and likely some thermal bridging as well, where the framing itself conducts cold into the conditioned space. Because heat moves are not cold, and the images were taken in the winter, the thermal bridging is heat moving out to the exterior rather than cold moving in.
Other images, looking at where the brick exterior meets the concrete foundation, showed a similar story at the bottom plate. Again, the thermal imaging pointed to a combination of air leakage and thermal bridging right at the wood-to-concrete transition.
Why These Two Locations Are So Challenging
Top plates are notoriously difficult to seal. This is the zone where your attic, your conditioned living space, and your exterior soffits all converge. Getting a continuous air barrier across that intersection is a legitimate construction challenge. One proven approach is using products like SIGA’s Majvest on the exterior and Majrex on the interior, lapping them over the top plate and taping them to create a continuous barrier, inside and out.
Bottom plates present a different problem. Concrete slabs and foundation walls are rarely perfectly flat or level, which makes achieving a solid, consistent air seal extremely difficult. Foam, caulk, and liquid sealants have all been used here with varying success. A more reliable solution is SIGA’s Fentrim 430 Grey, an adhesive tape specifically designed to adhere to concrete. With a 2-inch bite on the concrete for warranty, it covers the bottom plate connection. For a truly continuous system, the approach also involves running the slab vapor barrier (such as Stego Wrap or 10-mil poly) up the interior of the foundation wall and underneath the bottom plate, effectively connecting the floor system’s air barrier to the wall air barrier.
Why Airtightness Matters More Than You Think
Most homeowners focus on insulation, and rightly so. But insulation without air sealing is like putting on a puffy jacket and not zipping it. Air infiltration bypasses the thermal resistance of insulation entirely, carrying heat out in winter and pulling it in during summer. The top and bottom plates are two of the most critical (and most overlooked) details in any building enclosure.
If you’re building new or doing a deep energy retrofit, don’t treat these as afterthoughts. Treat them as primary details, because your thermal camera will absolutely find them if you don’t. Want to talk details? Our team is always here to dive into the details of air tightness!
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