Thought I would share this with those folks who perform thermography services with home inspections, especially our up-and-comers like Paul and Frank. I can never tell if the answer is going to be obvious to everyone, so I apologize if this turns out to be a no-brainer for you.
Here are two recent examples of air leakage at interior walls of new construction homes (blower door tested homes).
Both examples are interior 1st floor walls (no exterior exposure on either side) of 2 story homes. The houses are under slight negative pressure. Interior temperature has been stable for some time so we should be near thermal equilibrium. Pretty narrow temperature span on the images
In the first example outside is cool, interior is warm. Air leakage through switch boxes installed in the sheetrock.
In the second example outside is warm, interior is cool. This is a laundry room which backs up to staircase with the under-stair area fully sheetrock enclosed (no access). The first image shows the location of the studs as cool compared to the sheetrock (would you expect this on an interior wall?), the second image shows air leakage around a metal clean out cover for the washer drain.
Where might the air leakage be coming from? What would you look for? I have photos of the answers which I’ll share. Do we care about the air leakage when the temperature difference is so small?
If the air leakage isn’t coming from the sides or below, it’s coming from the attic. If it’s leaking out at the first floor, it’s going to be coming through a chase.
In the first example, the chimney fire-stopping was not sealed in the attic so the air was entering through the chimney chase (you can see the fireplace in the first visible light image above).
In the second example there is simply an open chase adjacent to and above the staircase. You can see the plumbing vent from the clean-out image going right through the chase.
The builders acknowledged and corrected both issues. So while these thermal images would be unremarkable on exterior walls, on interior walls they usually indicate an issue in the attic that’s worth tracking down.
A home is under pressure. Add shear and up goes the points of entry.
1: The envelope under the most pressure.
2: The void in the two part system, the mid assembly is under middle pressure.
3: The conditioned space under the lowest pressure.
