I’m insulating the rim joists of a kitchen ceiling but have come up against a real problem. At one end it is impossible to access the space above the plate because there is a second joist installed inboard of the rim joist, right at the edge of the plate, with only a 1/2″ crack between inside plate surface and bottom of joist; walls are 2 X 6 and joist are 91/2″ TJI.
Short of drilling holes and applying expanding foam, I’ve no other ideas about how to accomplish this. Making the matter more difficult are a number of wires running across the face of the second joist. This is really something the original builders should have addressed, probably with rigid foam sandwiched between joists.
Had the wires not already been run I might have considered putting another joist in and scarfing out enough of the existing joist to work some batt insulation into that cavity but that train has left the station.
Idears?
Replies
It's a common problem
tuanj wrote:
This is really something the original builders should have addressed, probably with rigid foam sandwiched between joists.
Couldn't agree more. We always buy rigid foam board with our framing packages in order to address this problem WHILE framing so as to not screw the insulators (not to mention client) AFTER we're framed up and it's time for them to establish a proper thermal envelope. We use cut to fit rigid polystyrene on exterior wall channels as well during wall panel sheathing. We've demo'd plenty of production home walls where these areas were completly uninsulated. As remodelers and renovators we can afford (and know enough) to do this. Most production builders cannot; which is a shame. IMO, overlapping trade details are the first things to get missed or tossed in the production building sequence. However, with insulation and air sealing becoming more of an issue than ever (blower door testing now required in some areas) I think this problem will fade.
Your idea of drilling access holes for spary foaming these cavities is probably your best and most cost effective solution. I would drill plenty of decent sized holes so that you can access the full areas and verify good coverage. I would use the spary foam (parts A&B) kits for this operation rather than one part cans.
Hmmm...
tuanj wrote:At one end it is impossible to access the space above the plate because there is a second joist installed inboard of the rim joist, right at the edge of the plate, with only a 1/2" crack between inside plate surface and bottom of joist; walls are 2 X 6 and joist are 91/2" TJI.
Short of drilling holes and applying expanding foam, I've no other ideas about how to accomplish this. Making the matter more difficult are a number of wires running across the face of the second joist.
So if I follow your description correctly (see attached) you have a void above your wall plate that's 9-1/2" deep and 4-1/2" wide?
With a 1/2" gap between outdside bottom edge of that inner joist and the inside top corner of your wall's top plate?
Does that 1/2" gap run the full length of the wall you're working above? Can you see what's above the joists that could be used to contain expanding foam?
I don't see any problem using spray foam to fill the void thru that 1/2" gap. You may need to extend your applicator by some means to get foam up at the top of the void initially, particularly if there's other insulation above you don't want to displace.
Rather than counting on one application expanding enough to fill the entire void all at once perhaps first place a layer at the top then once that's set up it'll contain what's placed underneath.
(I'd be very generous with deploying cheap polyethylene drop cloths too under the gap and on exposed surfaces well wide of your work area. Falling foam will be a PITA to clean up otherwise.)
Even with the wires you mention I don't see why drilling holes in that inside joist'd be required if the void has a 1/2" access gap its full length.
Roger on the schematic (where can I find the tools for drawing that nice schematic?) but I think the gap is less than 1/2". Which is why I really think I will just have to drill some holes and follow the advice by doing a partial fill then waiting. The problem is seeing inside, which I can do with a flashlight through the gap. Above the joists is a 3/4" plywood subfloor.
This is an expensive job to keep an insulation envelope complete: $299 at the Depot for 2 part spray foam w/applicator, for an amount that will cover 200 bd ft (their claim) which might just do it, might not.
Like a friend said, you chase your screw-ups all the way to the roof. Or someone elses in this case.
Thanks to both responders.
Might be worth investing in a cheap inspection camera.
Do the Math
tuanj wrote:(where can I find the tools for drawing that nice schematic?)
I use Adobe's Illustrator application. I have it left from when I used it to earn a living.
There are other vector drawing programs out there that'll cost you less, I'm just not savvy as to where to send you to look.
This is an expensive job to keep an insulation envelope complete: $299 at the Depot for 2 part spray foam w/applicator, for an amount that will cover 200 bd ft (their claim) which might just do it, might not.
Um... how long is this void?
200 board feet is quite a volume; working backwards I come up with just over 56' for a void given your sectional dimension.
The 2-part kit @ $1.50/ bd.ft. (144 cu. in.) would be a bargain if your void is really that long!
Using 16 oz. cans of Great Stuff Big Gap Filler @ $4.96 each (literature suggests 1 can = 24 tubes of caulk, ~ 2.8 bd ft) cost would be $1.77 / bd. ft. if my pencil's sharp enough.
If your run is something more like 12' - 16' economics maybe favor a few cans? 1' of run = 3.56 bd ft or 513 cu. in.
Or the 15 bd ft 2-part kit from HD for $34.95 maybe? @ $2.33 / bd ft. it depends on how long that void really is I guess.
Any of these'd be preferable IMHO to stuffing fiberglass up in there somehow.
Thanks-again-for indulging me...The length is about 17 feet. Game plan has changed a bit; owner understands the importance of continuous insulation but wants to look into every possibility. In the interim, I've closed the 1/2" gap* and sheetrocked the ceiling (job couldn't wait any longer) so any insulating will have to come from outside. Now it's January and not a particularly good time to be spraying the stuff in anyway. Fortunately the exterior wall still is bare of shingles so instead of drilling holes inside it will be through exterior 5/8 " sheathing and whatever thickness the rim joist is. I honestly can't see how anyone could possibly do a complete job (no voids) using only hand-held spray foam in what is essentially blind insulating. The pros -from what I gather from second hand info- have a better sense of when a cavity is filled by the behavior of their applicator-and one of them is coming by tomorrow for a gander. It may be considerably more to have a pro do it but I think the odds of their getting it right are better than mine; if the client wants to pay for it, I guess who am I to say no?
*though originally i thought the gap would work to advantage, I eventually realized it would have to be closed in prior to application, as the foam would surely weep out of any gap that size
Yep, Good Idea
Passing the task on to a pro, that is as long as your client signs off on the expense.
Yes the foam applied thru the joist/plate gap would 'weep' as you put it but as long as adequate preparation everywhere underneath that extruded foam can fall off onto is done, what's left attached to plate & joist is easily cut away once hardened.
Too bad you'd not mentioned optional access going thru from outside; common practice for blown-in material is to drill large holes thru sheathing (sometimes siding too) into which nozzle gets placed during install. Issue here is proper vapor barrier when cellulose is the product being blown in. Closed cell foam removes this issue, would be what I'd look to use in your situation unless you renewed vapor barrier (6 mil poly under new drywall) when you finished up inside.