Hi all,

I encapsulated my crawl space this past year with 2″ foam board on the walls and a vapor barrier. When doing the encapsulation, I left 6″ from the top of insulation boards (4″ from the top of the vapor barrier), to the sill plate. This was to act as a termite inspection gap. I live in Indiana where there is “moderate” subterranean termite activity (fortunately, I have yet to have issues).  After talking with a few foundation companies, some recommended the gap, other’s said it wasn’t needed. Local code does not require a gap. Ultimately, I decided to have the gap.

One thing that a lot of people recommend to improve comfortability and energy efficiency in their home is to air seal and insulate the rim joist. I’m planning to do this with rigid foam board. However, I found that this 6″ termite inspection gap on the foundation wall is very cold. In fact, it is colder than the uninsulated rim joist. Using a thermal imaging camera, the wall with insulation is about 61 degrees, and the uninsulated termite gap on the wall is 49 degrees. I’ll attach a picture of the thermal image and a normal image (ignore mold stains). 

How big of an issue is this uninsulated area? Is this area worth insulating? I’m sure it’s difficult to exactly say, but I’m wondering if this is causing me a noticeable difference in comfortability and energy efficiency/savings. It’s 6″ around the entire crawl space perimeter (perimeter is 142′). So in total it’s 71 sqft of uninsulated wall.

My plan was to fasten some 2″ rigid foam boards (R10) over this gap. While not everyone would recommend it, I feel comfortable enough to do it. I’d still leave a small gap for inspection and could remove the foam board if needed without tearing out the vapor barrier. I also have a termite shield. While the termite shield will not prevent termites from reach would, it does force them to tunnel around the shield, making them more visible. For that reason, I feel a bit more comfortable insulating this area if it would make a difference.

My concern is that this uninsulated area of the wall is causing me a noticeable amount of loss in energy savings and comfortability. While the rim joist is a slightly larger area, the fact that people see improvement by just insulating that area, makes me think I would see improvement in insulating the cold area of the wall.

Thanks!