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How much spray foam in floor/ceiling?

Posted by pjb999 (My Page) on
Tue, Mar 31, 09 at 14:28

I need to replace my garage ceiling, which is below my master bedroom because it was lined with thin plywood which I don't consider very fire-safe. Also the floor above is usually quite cold and I want to get rid of the carpet in there. Cutting a few exploratory holes, I see the insulation that was in there has dropped out of the joists, and there was no moisture barrier laid over the ceiling joists (go figure) - An unexpected bonus I suppose, that the garage rarely dips below freezing but I'd rather have a backup heater in there for that! Location is central British Columbia, a fairly high altitude so it gets pretty cold.

I think sprayfoam is the way to go, since it'll hold itself in place and serve as a moisture/air barrier.

I've priced doing it myself, and getting it done, and it looks like by the time I buy the stuff from Tigerfoam (only Canadian supplier I can see, any suggestions for other suppliers, keeping in mind I'd have to ship and pay tax at the border) I wouldn't save much on paying someone to do it, in fact on the face of it, the kit'd cost me more. He was suggesting around 3" which would be R-21 (R-7 per inch) - I would have to buy one large, one small kit to do it, so I'd be in slight overkill. On the upside I have a couple of small areas I'd like to retrosprayfoam....which I might have the guy do if I get them in.

I was figuring on putting the original fibreglass insulation back up there after the sprayfoam has set, on the assumption you can't have too much insulation, and throwing the stuff out sounds silly, I suppose I could stuff it up in the attic but it'd be messy moving it up there. To keep it in the joists this time, I could staple string up there or something to hold it til the drywall goes in?

My alternative would be to buy sheets of foam and cement it up there. A lot more work I guess, but I wonder if it's cheaper to do that. What new construction I've seen with sheet foam seems to be something around an inch thick with a cardboard face, with acoustic sealant caulked around it (they have pretty tough rules about airtight seals these days) - I assume they may put fibreglass up there too since I don't imagine this foam board stuff is enough. The board goes directly under the flooring so it's on the warm side. If I put hardwood up there I might be worried about the brads knocking the board loose.

What are your thoughts on this, and if the foam board is an option, do you know what the cardboard-faced stuff is called? I wonder if it's part of a fire-retardant thing or something which shouldn't be an issue for me since there'll be drywall up there.

The ceiling area is 270 sq ft, there are some drain pipes from the bathroom upstairs, which the insulation guy I spoke to would spraycoat so they are lagged, so I don't have to worry about them being on the cold side of the envelope. I know having to do any future plumbing work would involve cleaning the foam off, otherwise I'd have to build some sort of box around them to keep them on the warm side, which would present some issues since there's not much space below the pipes to insulate.

So 270 sq feet, insulation guy quoted me cdn $ 4.50 pst for 3" + 5% GST = $1275 plus extra if I get the other small areas done, vs tigerfoam -

The specs for tigerfoam:

ASTM-E84 (American Society for Testing Materials)
Flame Spread = 20 / Smoke Developed = 200 / Perm = 1.2 @ 3"
Fuel and water resistant
UL-94 HF-1 (Underwriter's Laboratories)
International B2 Fire Rating
Complies with U.S. Clean Air Act & Montreal Protocols
CHEMTREC #201586 - 800.424.9300

So no formalehyde, no VOCs.

Would I need 2 x 600 sqft kits to get 3" (cost CDN $1816.50 inc tax & shipping) then I'd probably have more left over than I could use, but apparently to do a ceiling or crawl you don't deduct for the joists. Maybe I'd squeeze through with one 600sqft which would make it CDN$929 inc tax and shipping - that would be just over 2" worth I assume you can go back over existing foam to do a second layer if you have leftovers?

They say that you have 5-6 days to use up the remnants so I'd need to have every other possible place I might want to insulate (any suggestions? I'd love to re-do the rim joists but can't really get to them unless I drill a bunch of holes in the downstairs ceiling, pull the fibreglass back (no vapour barrier on it as far as I can see, how silly is that? Needless to say there's that black staining on it, but not *quite* mould)

Or I could do a deal with a neighbour who needs some done...

Sorry this is so long. Would appreciate your thoughts on this.

Follow-Up Postings:

RE: How much spray foam in floor/ceiling?

Moisture barriers go on the warm side,but you're right, the insulation was probably woefully inadequate.

I'd definitely go with the Tigerfoam (closed cell foam). It will block the air and moisture quite well, even around the pipes, etc...

I'd redo the ceiling with properly done fire resistant firewall, properly sealed against penetrations (fire rated drywall and proper installation technique).

RE: How much spray foam in floor/ceiling?

The 'warm' side in this case would be laid across the ceiling joists, ie directly under my bedroom flooring. I can't see cutting and stapling and sealing with plastic, hence the interest in the spray foam.

Somebody told me, since it's an older house, everything would be grandfathered in and I wouldn't need to worry about firestop drywall. They lined the walls with regular 1/2" drywall over the plywood they'd used, but I figured since heat rises, I'd do the ceiling with 5/8" firestop drywall (here in BC at least, it has a special designation)

RE: installation technique, what should I be mindful of?

Do I need strips to nail to across the joists, or do I affix direct to the joists? Pretty sure there are strips throughout the rest of the bottom floor of the house, I don't have much experience with drywalling ceilings.

Is there a special mud to use?

RE: How much spray foam in floor/ceiling?

One option is XPS "blue board" available at local home centers. It has a similar R value to spray foam of the same thinness, with possible lower cost. it comes in a 2" thickness. Make sure you use a small foam kit to seall all of the edges. R value is great, but you also need to stop infiltration. This would go in easily if the garage ceiling is "clean" after taking down drywall. If you have things in the way, like pipes and wires, spray foam will be better.

I have used the 2-part Zerodraft foam kit - it is great. I would take down the garage plywood ceiling and spray *one kits worth of foam* until it runs out. You need just and inch or so to air seal the floor. Then, reinstall the fiberglass batts for increased R value. And of course put in a drywall ceiling and tape it very well. In the USA, I get it from, but you should have a more local supplier.

Good luck!

Here is a link that might be useful: Zerodraft Canada

RE: How much spray foam in floor/ceiling?

Thanks Klaire. I had thought of the 'blue board' although a lot of what I see is pink - what is the difference? I have also considered a thinner coat of spray foam and making up the difference with fibreglass. I would probably end up with less than an inch, using a 200' kit on 270', otherwise I would have to go with a single 600' kit, which would give me a couple of inches. If I did that, I'd be somewhat ahead doing it myself. If I go for the full 3" it's going to cost a lot more.

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