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insulation Q'S

Posted by hunter41162 (My Page) on
Sat, Feb 21, 09 at 2:46

Hello, hopefully someone can help me out.

Ok so I Put up 1inch extruded polstyrene and glued it to the wall. framed up my 2x3wall, not yet anchored down. Couple questions before I go any further.
1.What was supposed to be done at the top of a framed wall running parallel with the floor joists? as far as fire codes go. I have a two inch gap. I slid the xps up behind the floor joist to the subfloor. That covered 1 inch, the top plate will cover the other. is this going to be ok? Also do firebreaks absolutely have to be used inbetween studs extended to concrete?
2. What about the parallel joists? I am thinking of cutting smaller squares above the top plates and just gluing them in. Then when I cut the full sheets for the other wall notch around the joists to subfloor. ????essentially double insulating.
3. What, if anything, should be used on seams around the xps, like floor and in corners? would some caulk do anything? and is duct tape ok to use to tape the joints with?
4.I plan on adding 2 1'/2 inch xps for additional insulation in between studs and just sectioning to allow for running electrical. yes/no?

I have looked through every page and I am still a bit confused, never seems to be a defenite answer.


Follow-Up Postings:

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RE: insulation Q'S

1)Re: fireblocking. See this thread and links. (Generally, it seems fireblocking the top alone is sufficient. But if a municipal inspection is required, you should ask what they require.)

2) No problem in doubling foam insulation.

3) Caulk or foam. There are some good pics on one of the recent threads. No duct tape! Use builder's tape, such as Tuck, Tyvek or 3M.

4) The more insulation, the better. But after the 1" XPS on the wall, you can economize by using other types--eg., fg, cellulose, mineral wool, EPS. Yes, you'll have to cut a slit for board type insulation if you're filling the entire cavity.


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RE: insulation Q'S

What are you going to put in the rim joist area beside those two layers of 1" foam? Will there be fiberglass up against the rim joist with foam on the inside? I'd rather have the foam against the rim joist and the fiberglass on the inside, but I not totally sure on that.

I'm now 3/4 through putting foam boards in the rim joist area (so that it meets up with the wall foam) and it's VERY tedious and not cheap either. Maybe you could kind of come up the wall with the foam, make a right angle and cover the concrete and plate, and the go up to the floor above. Then stuff fiberglass in there. If the foam was 2" thick the vapor probably wouldn't condense on any cool areas.

You might be able to glue the blocks of foam as they make the turns with some kind of non-petroleum glue like polyurethane.

I was surprised at how much frost there was on the rim joist when I removed the unfaced insulation. I guess it would evaporate when it gets warmer, but still...


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RE: insulation Q'S

I have decided to possibly do just 1 inch of xps cut in squares in rim joist area, and seal around it with spray foam insulation to seal them up. Cut the main wall xps flush with the block.I still havent decided on whether or not I am gonna change things up so my top plate extends to concrete for a little bit of a firebreak. If the wall is gonna go its gonna go...


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RE: insulation Q'S

I was surprised at how much frost there was on the rim joist when I removed the unfaced insulation.

Illustrating perfectly the uselessness of putting fg in there as an air block or insulation. It only provides a home for mould.


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