Strange gap where extension meets house
I was checking my foundation wall for more missing mortar when I came across this weird-ass gap in the “L” where an addition that the previous owner had put in meets the original wall. I’m not seeing any house wrap or insulation or… *anything* there. I can’t even tell how far up it goes. I assume I should have someone pull off the siding and see what’s going on under there? That’s definitely beyond my newbie DIY-er skill level. I doubt that I can just close off the bottom with a foam board patch and call it a day. Anybody have any idea why the builder did that and what I can do to close it off?
And yes, that extension room has been damn cold during the two winters I’ve been here.
edit: I guess it could be a chase, but it seems weird for one to be exposed to the outside like that. And there’s already a cold air return on another interior wall in that room.