It’s the invisible part of your walls that nobody pays attention to, partly because it’s out of sight in some homes. And maybe it’s because it has so many names that nobody knows what to call it the darned thing: band joist, rim board, rim joist, band board, ribbon, box band, box closure, and header joist. But it’s all the same and the cavity looks like this:
If you have a basement with drywall on the ceiling, you won’t see it and you can’t access it. If you have a drop ceiling basement, you can’t see it but you can access it by moving some panels around. If you have a crawlspace, you have one of these, even if you can’t see it. (And you can access it, even if the thought of going to see it isn’t attractive!) Only houses built on a slab don’t have a rim joist.
Here’s why these things matter to your healthy home and energy efficiency: it’s a whole foot of wall that is usually uninsulated or underinsulated. Worse, this is typically one of the leakiest parts of a home’s assembly. And worse yet, if improperly insulated, it could cause serious health concerns. This is a big triple whammy. So what’s the fix?