help on installing xps on cinder block
OK, the 3rd code official I spoke to (he's an assistant code official) has said we can put XPS on the foundation wall and frame and sheetrock over it. Initially, they said the drywall had to be in contact with the XPS.
We're going to mechanically fasten the XPS onto the wall, using probably 2'x8' tongue and groove 2" XPS board. No one seems to sell the 4'x8' which I prefer in order to have fewer seams to tape. I have the following questions:
1. If the goal is to just fasten to the wall, then will 2 screws (one at center top and center bottom) be enough? Or should we use 4 screws per sheet (at the corners)? Or is there a benefit to screwing one in the center of the board in addition to the 4?
2. I know we need to tape the seams, but what do we do about at the top and the bottom of the board? Do we tape there or use foam spray?
3. We've got an interior perimeter drain that channels liquid to the sump pumps. Should we not tape the bottom of the boards then to allow any condensation or water to drip to the drain?
4. I've got cinder block columns as shown in the picture at the link below - do we just score XPS pieces to cover as much of the columns as possible (ex: along the sides of the column)? We will be framing 1/2" along the wall and then around the columns to maximize space
5. We've got what looks like an old window (see picture at the link) that was covered with cement, but it isn't flushed with the rest of the wall - do we need to cut XPS pieces to fasten directly on the window or do we just ignore it b/c it's fine as long as this space lies underneath the 2'x8' board?
6. It seems tapcons and fender washers are used - what about standard masonry nails?
7. What should be done at the rim? Use unfaced fiberglass insulation? It seems like a lot of work to cut XPS and then cover it with drywall (mandatory with XPS) at the rim in between all the joists.
thanks in advance for your help.
Here is a link that might be useful: foundation wall pictures