Hello, I found a "band" (14 inches wide across the whole back of the house) of some kind of drywall product where the brick meets the vinyl siding on my house that is in place of plywood. Anyone know why this is here and why it isn't just plywood? I had to remove some siding and tar paper when I tied my porch roof into the structure and found this weirdness. It is original (1975) because the tar paper had never been touched but it is crumbly and needs to be replaced. Behind this drywall is open joist space of the second floor with very little insulation (now I know why the floor is so cold in the winter!). Thinking of closing this off, spray foaming and re-sheathing with regular exterior plywood. Do you think the builder just ran out of plywood and used drywall for sheathing or was there a purpose for this back in the 70's? Photo attached (click the attachments button in the menu)...just curious.

So i am remodeling our kitchen, and have removed all of the various layers of wall from 90 years of remodels. on the exterior wall, there was once a window and a door in the brick wall. Currently there is a timber header supporting the brick then wooden studs in the opening. The exterior is clad in stucco. Behind the stucco was once some sort of sheathing, looks like brown particle board, sort of like what peg board is made of, but thicker, and the remnants of a sheet of tar paper. either way it has allowed some water in, and is cracked and falling off. there is roughly a 1/2 inch space between the stud and stucco where this spongy decomposing backer has fallen off. The plan was to go from a 24x36 window to a 36x48 window... but now i am not sure if i can properly waterproof the wall and / or sacrifice this stucco in the process. The stucco is solidly attached, and doesn't feel as though it will come off. the whole area is roughly 6ft wide by 8 ft tall. Does any one have any thoughts on if this stucco needs to be replaced, if it would be possible seal the inside in some way and then integrate a new window without water leaks? [ATTACH]34912[/ATTACH][ATTACH]34913[/ATTACH][ATTACH]34914[/ATTACH][ATTACH]34915[/ATTACH]