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Old 01-08-2011, 06:41 AM   #31
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rim joist insulation project question


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I'm finally getting to this project. With the energy credit running out I was compelled to buy a several 4'x8' sheets of R10 2" closed cell foam board and a bunch of great stuff cans. Tomorrow is the day I tackle it. I'll make one final post with the results and maybe a picture.
I did all my rim joists a couple years ago, but didn't use Great Stuff. If you ever need to remove the foam blocks, to inspect for termites/carpenter ants, or moisture, I think you'll regret it. I just cut the foam to fit tightly against the rim joist--the foam block has some "give" to it. For the few areas that weren't tight, I used silicone caulk.

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Old 01-09-2011, 08:09 AM   #32
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rim joist insulation project question


This issue of access is why I avoid the closed cell board in some areas along the rim, but the rim joist still breathes with plain rock wool.

My bigger issue is the one wall running 25 feet where the rim and the first joist are only 3.5" apart.
the only access I have is to section reflective, rigid foam and tuck it above and back against the joist. I cannot seem to reach my foam gun deep enough to seal above the sill plate and at the top where the rim meets the underside of the floor, so I may resort to silicone globs on the tip of my gloves and smear the wall. If anyone has flex tube extension or similar for a foam gun please let me know.

I too have lowered my gas consumption substantially, over 35% and counting from the total project so far and am now boarding the walls with R10.5 closed above grade, R10.5 open cell below and then will cover with r13 mineral wool, fireproof. I have read on buildingscience .com that this hybrid technique will allow the walls to breath. Much more expensive this way but I lucked out materials at 1/2 price at a building center which was closing.
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Old 01-10-2011, 02:09 PM   #33
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rim joist insulation project question


I was also asking about this when this thread was originally posted. I ended up doing essentially what Chemist talked about - a bead of Great Stuff along all the inside corners within in each bay (top, bottom, both sides, as well as 6 - 8" "back" along the underside of the subfloor and the top of the sill plate). Then a clean cut piece of Roxul (R22) in each bay.

I checked them recently (going on 2 years since then) and when I pulled the roxul in a few spots it was clean and dry (did this last year and this year too). Overall very tedious work but a couple bags of roxul and a few cans of great stuff was under $100 to do @1000 sq ft.

Chemist this is probably no help to you but I made a "poor man's" foam gun when I hit the tight spots in my crawl space (could not get access with a regular can - I had no gun to begin with). Ok - don't laugh - I had a few feet of clear tubing leftover from another small project - might have been 3/8 "..? Anyway I slid this over the end of the plastic straw that comes with the great stuff cans (a very tight fit - about an inch or so is all I could get). Then taped a very small diameter piece of dowel near the end, and used that 20" or so contraption to get the end of the clear tube right into the tight spots. It held up - crude and a bit messy (no perfect bead or anything) but it did the trick.
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Old 01-10-2011, 03:17 PM   #34
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rim joist insulation project question


I was looking at having my rim joist spray foamed, but you guys have me questioning that decision. Foam would have been just 1" thick to seal the area. Over the foam I was planning on R13 Roxul.

So its best to just air seal the wood contact areas (mud sill, rim joist, sub-flooring and floor joists), then batt insulate?

RToni - Are you saying that you used can spray foam and sprayed the underside of your sub-flooring? Is there batt insulation over the foam? Faced or unfaced?
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Old 01-10-2011, 04:22 PM   #35
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I was looking at having my rim joist spray foamed, but you guys have me questioning that decision. Foam would have been just 1" thick to seal the area. Over the foam I was planning on R13 Roxul.

So its best to just air seal the wood contact areas (mud sill, rim joist, sub-flooring and floor joists), then batt insulate?

RToni - Are you saying that you used can spray foam and sprayed the underside of your sub-flooring? Is there batt insulation over the foam? Faced or unfaced?
I really need to get a camera to make up for my bad descriptions

Essentially I went into each bay with the can and any corner where framing members meet (the floor joist meets the rim joist / sill plate / subfloor) I ran a bead of foam, including where the top of the joist meets the underside of the subfloor. Once it was sealed in the corners, I cut a piece of the R22 Roxul to fit snug in the space. Very easy to remove and inspect, which I've done a couple times now in random spots.

If I had a big bag of $$$ I would have called the spray foam guy in a heartbeat too, but I didn't have the budget for it. The pro's might say that's still the best way to go (seal the rim joist completely inside) and as a DIY who am I to argue. I saw the tanks of DIY foam stuff show up on a rack in the local bulding supply - I thought "great" - but then saw the almost $500 sticker and walked away. So if you have some time and don't mind the tedious aspect, a poor man's approach is much easier on the wallet and might work for you. After reading a lot of discussion here I gave it a try and so far so good. Just adding my 2c to let you know it seems to work well for me but there's lots of good discussion here IMHO to help you decide...
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Old 01-11-2011, 01:25 PM   #36
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rim joist insulation project question


Now I'm really confused.

Is it really necessary that you periodically look at the rim joist for moisture issues? Probably nothing wrong with looking, but once you seal the area (full spray foam, foam board, or just caulk) shouldn't that be it?
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Old 01-11-2011, 02:06 PM   #37
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Now I'm really confused.

Is it really necessary that you periodically look at the rim joist for moisture issues? Probably nothing wrong with looking, but once you seal the area (full spray foam, foam board, or just caulk) shouldn't that be it?
seems to be what I do best (confuse people) - as you can see by the threads here and elsewhere there's a lot of discussion and a few different approaches to solving this problem. add to that the fact that I am a DYI'r - so sanity checks are the norm for me and this is a really really easy sanity check. In the 5 minutes it takes (literally) while I'm in the crawl space working on something else I can pull a few random chunks of insulation and take a quick peek in those spots - not everywhere - hope that's not what I implied). A random check - and if there is a problem (like moisture) I catch it and deal with it. I'll do this a couple times a year for a couple years (let the house cycle thru a few seasons) so I really know it's working for me. It just helps me sleep at night.
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Old 01-11-2011, 03:13 PM   #38
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rim joist insulation project question


Thanks rtoni.

I completely understand your wanting to sleep peacefully knowing the rim joist is not rotting away.

I was only looking for the scientifically approved method. Maybe there isn't one.

I don't want to find out six months later that the building code now say NOT to completely seal the rim joist area after I just spray foam sealed it.
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Old 01-11-2011, 04:18 PM   #39
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rim joist insulation project question


no problem - guys who've done a hundred of these can probably offer better advice on what works best or may be required in your area / circumstances. I figure in my case if my approach bombed, I haven't painted myself into a corner, so to speak - it's not a fortune invested and I can easily undo it all even in the worst case (pull the roxul out and / or add rigid foam board, spray foam everything, etc.). Things to consider IMHO. I guess you can say I took a bit of a chance (a bit of time invested) and it's working out - so now just offering up that experience fwiw. Good luck with whatever you end up doing.
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Old 01-24-2011, 03:07 PM   #40
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rim joist insulation project question


Just finished insulating the headers with 2 layers of 2" XPS (I used formular c-200), sealed repeatedly with silicone and sprayfoam. I found that unless I left VERY big gaps between the XPS and the joists, the spray foam bead wasn't 100% air sealed. It sticks to the xps pretty poorly when first dispensed, and about 1/2 of the narrowest beads I did ended up useless (with holes allowing air to pass through). I ended up using silicone to seal, which is tiresome but worked great in the very small gaps as I cut it. It was a huge pain in the butt cutting tight little rectagles on the two walls that meet the joists (they look identical, but they're not). They are warm and dry right now during the nasty cold snap we're getting in Ontario at the moment, so I guess I should be happy

If you're looking for fast, I'm guessing the guy who did sealing and Roxul is laughing, assuming the air sealing worked out well. I'm proud of the work I accomplished doing two layers of c-200, but it was a lot of time. I wish I'd read the trick about using a table saw with special blade to cut xps before I started. I did everything with straight edges and very sharp utility knives and that sucked...

BTW, you need to check the adhesive you're using if you're doing two layers of formular. RONA has contractor tubes of PL300 for the first layer (affordable), but when you're sticking XPS to XPS you can't use PL300 and you end up having to buy the more expensive PL9000 (which I could only find in the smaller tubes).

To be honest, I liked PL9000 better anyway but it's costly. PL300 requires the board be mechanically attached while it cures, which gives you an extra job to do later on, since screwing it in place with a washer or bit of strapping is okay, but the screw is a thermal bridge you're going to want to remove later and fill the hole with foam.

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Old 01-24-2011, 08:33 PM   #41
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rim joist insulation project question


Man, you guys are killin' me. Part of the plan for upgrades this spring included budgeting for a spray foam kit specifically for this, the rim joist in the crawl space. Now I read through this thread and apparently that all needs to be rethought, as if Gary's damning indictments of OSB weren't already enough.
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Old 01-25-2011, 06:20 AM   #42
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rim joist insulation project question


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Man, you guys are killin' me. Part of the plan for upgrades this spring included budgeting for a spray foam kit specifically for this, the rim joist in the crawl space. Now I read through this thread and apparently that all needs to be rethought, as if Gary's damning indictments of OSB weren't already enough.
Not sure there's a formal downside to spray foaming them. I would have done that myself but couldn't afford it.
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Old 01-25-2011, 07:01 AM   #43
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rim joist insulation project question


I just had the crawlspace cleaned of mold so now the rim joist project is quickly approaching.

What exactly is the point of installing the foam board if you plan to insulate over it? Couldn't I seal the rim joist wood contact points with silicone caulk then cover with Roxul? Silicone would seal the air infiltration points and the Roxul would provide some insulating value.
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Old 01-25-2011, 07:10 AM   #44
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rim joist insulation project question


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Not sure there's a formal downside to spray foaming them. I would have done that myself but couldn't afford it.
Understood, but when I hear comments about access to check for moisture and insects if just makes me stop and rethink one of the things I thought I had settled. But then, that's why we're here, isn't it?
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Old 01-25-2011, 09:57 AM   #45
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Understood, but when I hear comments about access to check for moisture and insects if just makes me stop and rethink one of the things I thought I had settled. But then, that's why we're here, isn't it?
Yes indeed

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