before I frame / Drywall... XPS / Fireblock Q's

15 years ago

I am at my last chance to fireblock...not sure it will ever be inspected, not sure if the house went up it would make a difference but if somehow the folks from PA ever had to inspect it, it would be nice to be up to code.

The top edge of the XPS likely needs to be capped. I have 3 walls that range from having a concrete ledge 3/4" deep to sill to 8 " deep to sill.

Would it be best to simply tack up a drywall stip to the rafters...if so, how wide?

In some areas I could nail a 2 X 2 into the sill..sometimes it would rest perfectly against the sill other times it would stick out past the XPS. Some areas I could almost lay a 2 X 4 there...not sure how I would secure it to the concrete ledge...liquid nails? Hate to have the pt wood on the concrete ledge, then again regular wood (sill) has been resting there for 20 years. Maybe I should just leave it go? The dywall method seems easiest, so what would you do?

I had limited room between the stair stringer and wall. I was forced to affix 1 X 4 pt wood directly to the concrete. I filled the space in between with 1/2" DOW. I tacked the top of each DOW strip in place to temporarily hold it in place. Do I need to add fender washers to get the rest snug against the concrete or can i just leave it sit there? The 1/2" is so thin I am not sure it will ever all be completely against the concrete. Note the pt wood is a little deeper than the dow so the drywall, unfortunately will not push it into place. So, leave it go or what?

Finally, I left my fir strips an inch or twp above the floor. I actually already have filled in the slot you see in the pic with foam. Do I need to anything along the edge of the XPS at floor...caulk, foam or it is ok as it is?

Comments (5)

velvetfoot
15 years ago
I put latex caulk there.
sparkywannabe
15 years ago
Top blocking: Put the drywall up there if you can, extending to the concrete or sill on the exterior side. If you are putting in a suspended ceiling, then it doesn't matter if it extends a bit past the top plate on the interior side. The goal is to cover any gaps at the top of the wall that could communicate with the space above the ceiling since there is only drywall on one side of the wall.

Bottom of XPS: Like velvetfoot, I caulked the bottom edge of the XPS where it meets the concrete. It shows this in one of the Building Science documents.
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andrelaplume2
Original Author
15 years ago
so in PIC #2 remove the 2 X 2 and add a say 6" wide (more ???) piece of drywall, screwed to the rafters as far back as it will go. Thus nothing touches the top ledge of the XPS but rather there is a inch or so gap between the XPS top ledge and drywall. I assume then when I am drywalling or framing in front of the XPS, there will always be a inch gap there.

How about the blue DOW stuff. Just shove it in as best I can, caulk the bottom and tyvek tape the sides? Simple enough but the stuff might not end up tight against the concrete...there could be and 1/8" space in some areas since its not very rigid. (again, the 1 X 4 isticks out a little more tan the DOW so the drywall will not froce the dow tightly against the wall.)Is the general feeling though that I need not tapcon the blue pieces in place? That will save a lot of work.
rmlsll
15 years ago
Does andreleplume2 need to pull off the thin plastic film that Dow attaches to both sides of their Styrofoam (3rd & 4th photos) so that moisture on the basement walls will dry toward the interior per Building Science suggestions?

I'm new to this site, but I searched back quite a ways and haven't seen an answer.

The climate here 50 miles north of Atlanta is relatively mild and I was planning to use a system similar to andrelaplume2's, with 3/4" styrofoam against the poured walls, and a 3 1/2" stud wall with R13 on the interior. When I brought home some of the blue Dow stuff I noticed the film. It looks like it might be a vapor barrier, and as I understand it that would not be desireable.
andrelaplume2
Original Author
15 years ago
I pulled it...guy in Lowes said it was fine to...not sure why it was on there....

I am tyveking the sides against the pt wood and caulking the bottom along the floor..I determined its to thin to secure with fender washers; no matter where I put them there would always be spots bowed out a bit. The drywall will help a bit. I really eanted it flush with the wall but what can you do. This wall is actally under the back end of the garage and always felt the warmest--would not imagine any moisture problems. Note I am also using that caulk stuff meant for foam...does not really grip well though.