XPS / Fire / Overkill

andrelaplume2August 4, 2009

So last night I was capping the exposed top ledge on my 1.5" thick XPS that I put on my walls. I was capping it with 2" strips of drywall. Several areas I simply could not cap. Others the drywall cap came very close to my concrete sill which I did not like. I could not help but think I was wasting my time but if ever inspected I wanted t cover my butt AND apparently it provides some level of safetyÂarguably I guess.

So as I struggle to cap (and line my joists with XPS too) it dawned on me, whats the difference if I leave the top ledge of XPS exposed to the floor joist above. I read here how folks have foam blown into their floor joists. In that case you have foam against the wood of your floor aboveÂwhy would it matter if I did not cap this stuffÂ.maybe, even after reading all the threads here, I am still confused.

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Congrats for working on the basement during the summer. I haven't touched anything down there for months, except when the whole house water filter sprung a leak, but that's another story.

I'm no expert, but aren't you putting drywall on the ceiling? Wouldn't that do the trick?

I mean, the idea is that a fire starting in the basement won't spread as quick as it could. If the fire was on the first floor, your first floor underlayment would have to burn before it got to the foam, and at that point...

    Bookmark   August 5, 2009 at 11:38AM
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no...dropped ceiling.

I understand the issue...somehow the foam behind the dry wall catches fires and starts to spread....the cap along the top ledge of XPS slows it down, once thru its on its way to the floor above...which again slows it down...BUT...the folks who have the foam blown in...what do they do, I mean the floor above is actually the cap...ergo that should count as a cap for me as well...no?

    Bookmark   August 5, 2009 at 11:48AM
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I always thought the issue was when something on the floor sitting next to the wall caught fire and the foam caught fire. You put that stuff in the band joist too and covered it as well? Seems like you're knocking yourself out for that little piece.

I wonder if I can ask how the drywall on the firring worked out? I'm doing my whole basement (eventually) like that.

    Bookmark   August 5, 2009 at 2:45PM
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Yea, I am overthinking it....eventually an electrical inspector will come in. If he says I should have or need a framing inspection I wanted to be up to snuff...and safe. I really should have just got the permit and rules from the get go and taken my chances with the taxes and crazy rules.

As far as the slotted XPS over concrete, held up by the fur strips in the slot and the drywall over that.....it was very simple to do EXCEPT in some areas where the walls bow in or out. I had to shim here and there when putting up the drywall. Note too that you only get around an R9. The living areas I am studding out in front of the XPS and adding R13 fg. All closets and my storage room though are simply the XPS. Over all it will be way more insulated than before I started and I save an extra 4" space or so in those areas.

    Bookmark   August 5, 2009 at 3:57PM
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Actually I was wondering how the drywall 'works' mounted on the firring strips. Does it look good? If you remember, I mounted 2" foam on the walls with firring strips and then put another layer of 2" foam over that by milling some grooves in the foam and then gluing it on. I haven't finished it totally yet and still have to put the drywall on.

    Bookmark   August 5, 2009 at 9:47PM
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Well, thats great insulation. I might be a bit concerned about how you would now attach your dry wall...I guesss through the outer layer of XPS and into the fur strips..likely need a 3" screw...? If you walls are not bowed the dry wall should go up easy.

    Bookmark   August 6, 2009 at 11:13AM
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Yes, that's my plan.
I wish I was as far along as you, but there'll also be window and stair treatments to think about too.

    Bookmark   August 6, 2009 at 11:23AM
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