Requirement for covering foam
NICK KEENAN
| Posted in Building Code Questions on
I have a house built in 1976 with no basement insulation. I am planning to insulate the walls with sheet foam and then a stud wall with batt insulation between the joists.
My understanding is I have to put some sort of covering over the insulation. Since I will use this area for a shop I don’t want to use drywall, I’d rather put some sort of wood sheeting (plywood, OSB or even paneling) that I can screw things to to hang tools and shelves on the wall wherever I want. Does this meet the fireproofing requirement, or do I have to put drywall under the wood paneling?
Also, do I need fire-blocking at the top of the wall?
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Replies
DOw thermax is rated for interior exposure so you could cover it with whatever you choose.
Don't understand the fascination with interior stud walls in front of concrete walls, seems a waste of material, and floor space, but that is just me.
I want the studs to hold shelves or cabinets or racks. I worry that strapping over the insulation attached through to the concrete would need an enormous number of fasteners to have the same holding power. With a stud wall installation is much simpler, you just attach the top plate to the joists and bottom plate to the floor. It also simplifies the installation of the foam board as the stud wall holds it in place.
I'm thinking of using steel studs in a 2x2 size to cut down on the thickness, with a wood panel facing that's a strong assembly.
My experience with steel stud is that they are not good for attaching anything to. Maybe there is a different style than what I have encountered.
It you really need extra holding power, you can do 2x3 or 2x4 flat instead of strapping.
You can also always mount shelves through to the concrete with long screws.
from a frequent contributor:
https://blog.energysmiths.com/technical/page/2/
23/32" or thicker plywood is acceptable. The code says 23/32" wood structural panel, which think includes OSB, but I would have to check that.
See comments here:
https://www.greenbuildingadvisor.com/article/thermal-barriers-and-ignition-barriers-for-spray-foam
Per Keith's comments, use 2.5-3" reclaimed polyiso to get R15 (I say that, but where are you?) and skip the stud wall. You can use 1x4 horizontal strapping screwed through to hold the foam in place. Wires can be run in the open space. In a shop I might just screw through the plywood and run wiring in conduit on the surface.
Dow Thermax seconds are available from some foam resellers and would not need any thermal barrier. My plan is to use this material at some point with horizontal strapping and probably just spray everything white. This way I can put drywall or plywood up as I want. Outlets in the wall would require a bit or routing out of the foam.
I'd argue that insulation and studs with 1/2" OSB is just as protective of the foam as 23/32" OSB. I don't believe that running wiring in a 3/4" void just under the finish material meets code, even though I've done it.
Joel, that may or may not be true, but code hasn’t accepted it in the US.
Rockwool has tested 2” of Comfortboard as a thermal barrier in the US. In Canada they have tested 3” of standard Rockwool, but I have’t seen approval of that in the US.
What about the wiring?
Oops, missed that, I admit that I don't actually know the answer to that. I haven't submitted any plans with this assembly or dug to find the answer.
I think Dana may have done this approach in his basement, so maybe he will be along.
Here in New England, we run wires in furred ceilings all the time, but that isn't exactly the same.
Its a shop, so one could use conduit, run it in the ceiling with drops, or run it in a chase and protect it with steel.
That is what I did in places where i could not get proper space to the surface.
3 1/2 = 13/4 to each side, thus one ought to be able to groove the back surface of 2 inch foam and be code compliant.
I cannot agree with building an entire wall just to put wiring in
edit
300.4 Protection Against Physical Damage.
(F) Cables and Raceways Installed in Shallow Grooves. Cable- or raceway-type wiring methods installed in a groove, to be covered by wallboard, siding, paneling, carpeting, or similar finish, shall be protected by 1.6 mm (1/16 in.) thick steel plate, sleeve, or equivalent or by not less than 32-mm (11/4-in.) free space for the full length of the groove in which the cable or raceway is installed.
Exception No. 1: Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
Or run wiremold on the surface. Or run conduit on the surface.
The studs aren't for the wiring, they're for holding cabinets and shelves.
Conduit and surface-mounted boxes in a shop make a lot of sense. They're so easy to adapt and expand.
Again, do what you please, but building a wall seems the most involved solution. Ikea style cabinets do not need a stud wall per se, nor would ' California Closet' style shelves
"And thirdly, the code is more what you'd call "guidelines" than actual rules"
Joel,
That's a joke right?
Edit: Just to clarify - Building codes are enacted by legislation. The requirements are legally enforceable, not guidelines. In most jurisdictions the code applies to the entire area in which it is enacted, whether or not there are inspections, permits or enforcement.
Yeah, definitely a joke. Your insurance company is going to think it is really a really funny one too if you ever put it a related claim.
It's only a partial joke (it's a line from "Pirates of The Caribbean"). I've had to design to code for 45 years. Codes get changed, manufacturers get their products approved, UL burns up assemblies, lots of money gets spent. I know too many designers who can't read beyond the written words in the code, I've seen projects built to code fail, and I've seen designers and code officials come up with some crazy "interpretations" of the various codes. A responsible designer has to know the intent of the code, and know what makes sense.
I kept trying to remember the movie and could only come up with Dazed and Confused. Pirates. Of course!
Another thought is to put up a stud-framed wall about a half inch out from the foundation and then have the whole thing spray foamed (closed cell). Thoughts on this approach? Probably more money and less work.
More money: 3” R16-18 reclaimed polyiso $0.63/sf, 2.25” R15.5 HFO ccSPF $2.81/sf ($1.25 /in/sf)
Higher risk due to potential for foam applications issues. Need to be out of the house for at least a day beyond when they finish.
Lower performing due to the framing factor.
You can pre run electrical, but any modifications are going to probably need to be on the wall surface.
My basement is 18x50, 8' high so 136 LF and 1088 SF. At a difference of $2.18 per SF the reclaimed sheet foam costs $2371 less. However, the wall is 3" thicker, so I lose 34 square feet. In my market houses sell for $400 per square foot, so I lose $13,600 worth of floor area.
And isn't polyiso not a good choice where it's exposed to moisture? Wouldn't EPS be a better choice? But three inches of that only give about R11.
So here's an apples-to-apples comparison:
The EPS that I've been able to find locally is Insulfoam R-Tech at Lowes:
https://www.lowes.com/pd/Insulfoam-Common-2-in-x-4-ft-x-8-ft-Actual-2-in-x-4-ft-x-8-ft-R7-7-Faced-Polystyrene-Garage-Door-Foam-Board-Insulation/3014190
It's $20.98 for a 2" 4x8 sheet, R7.7, or $0.66/SF.
To get an equivalent R-value would take 1.25" of closed cell spray foam. There is a Blue Seal building supply near me that has a 600 board foot kit for $650 delivered. That comes to $1.35/SF. So the difference in materials is $0.69/SF, or $750 for my 1088SF basement.
But:
1. I lose 2" of space all around with the board foam, or 22.7 SF.
2. The spray foam is less labor.
3. The spray foam is a better seal.
Please don’t use that type of spray foam except where it is the only option. It is HFC blown, which has a huge global warming impact. Also don’t expect to yield 600 bf out of the kit on a 50F basement wall. You get 600bf with under perfect conditions and perfect technique. If you really want spray foam, hire someone to spray HFO blown closed cell. The HFC version has a 1000 times greater global warming impact than the HFO.
See https://www.greenbuildingadvisor.com/article/installing-closed-cell-spray-foam-between-studs-is-a-waste
Time and time again taped sheet products, foam or sheathing, have been proven to provide a much better seal that spray foam in bays. Fortunately, a basement wall is pretty much air sealed, so there isn’t much drive.
Spray foam does make sense for complex geometry like rim joist down to the top of foam on walls.
Polyiso is fine in dry basements except maybe the bottom 4” where you can glue eps. Start the polyiso from there.
For a shop, the most compact setup would be 2.5” polyiso, with 23/32 plywood or advantech through screwed over the top. You are at 3.2” to the finished surface vs 4.5” with your set off studwall and drywall. 23/32 advantech is good enough to hang most thing you would hang from a studwall. Anything particularly heavy can be through screwed to the concrete. No need to worry about hitting studs too.
Thanks.
Now you've got me thinking. If I used Advantech, I think I might be able to get away with fastening it only at the top and bottom. I could do 2 1/2" of foam and run a 2x3 at the top and bottom*, fastened to the bottom of the joists at the top and tapcon'd to the floor at the bottom. Then screw the Advantech every 12" top and bottom. Since the Advantech is tongue and groove I think it would tend to support itself. The only concern would bowing. If the Advantech bowed I could fasten it along the tongue edge using 4" Tapcons. Tongue and groove materials are often attached only at the tongue side.
I have only inside corners, I could put a piece of 2x2 to tie the two walls together. I have a couple of doors that I could frame out with 2x3, that would really stiffen the whole assembly.
The 2x3 at the top gives a nice boundary for insulating the joist bay. Run the wall foam to the bottom of the joists. Put another piece of polyiso horizontal from the rim joist to the 2x3, then another piece vertical along the rim joist.
I'd probably want to leave a 1/2" gap along the bottom edge of the Advantech to keep it from absorbing moisture. I'd also probably want to paint it.
*(bottom would have to be pressure treated, and I've never seen 2x3 PT, so I would rip a 2x6).