Framing basement with foam board insulation
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I’m planning on using 2.5 inch polyiso foam board against cement walls to insulate my basement.
To finish the space, it was recommended to use 2×3 framing against the foam board, but lay the wood “on the flat”. This way, it takes up minimal floor space.
Would you have issues with drywall bowing by doing framing like this? Our basement ceilings are about 9 feet tall. In some areas, the ceiling is 11 feet tall.
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kickstarter,
When you use dimensional lumber on the flat it is more akin to strapping than a framed wall. To ensure it stays flat you should fasten it though the foam into the concrete behind at mid-span.
You often see these finish walls formed purely as a decorative element, lightly attached to the floor and joists above. They aren't attached to the exterior foundation walls, which cuts down on penetrations and potential weak points for moisture or condensation.
https://alleguard.com/products/construction/rigid-board-insulation/envirostrap/
Hanging drywall from 2x3 should not be a problem, any way you slice it. Drywall screws only need to fasten about 0.5" into the wood, and if you have 1.5" depth to work with, that'll be plenty. You can even drill through for electrical lines as needed. (Just be sure to use a nail plate if there's any cable or pipe less than 1" from the surface of the timber element, to prevent future accidents.) If you're using normal electrical boxes, though, you may need to carve out some of the foam behind in order to get the appropriate depth. They do make shallow boxes, but depending on how many wires are coming in and out, you have to calculate if these are too small a volume.
Hanging drywall against "flat" framing is so much easier than the normal way. In this case, you have a solid 2.5" width to land side-by-side sheets, rather than the typical 1.5".
Scott,
The problem isn't attachment, it's that a 1 1/2" deep stud has 8x less resistance to bending that a 3 1/2" one, so it is less likely to remain un-bowed without some fasteners in the middle.
And once you're fastening to the wall it becomes easier all-around to use a 1x4 instead.
DC,
I'm re-doing a wall in my dining room, which is concrete up to about the 4 ft height. I did a mock-up to see whether it was worth strapping the foam, or just use a 2"x4" stud wall. To me the loss of 2 1/2" is basically imperceptible.
Yeah, and the wiring gets a lot easier.
You are supposed to have 1" of the fastener in the wood. 0.5" really isn't enough to get a good hold.
As Malcom said though, just fasten the 2x3 to the concrete at both ends AND THE MIDDLE and you should be fine. Tapcons usually work fine for this and let you just drill all the way through the assembly and put in the fastener to avoid hole alignment issues between the different materails. The flat head tapcons are especially well suited to this application since you can drywall right over the heads of those when you countersink them into the 2x3.
For the OP: use 4" square electrical boxes for any wiring, then single or double gang mud rings to bring the devices (switches and receptacles) up flush with the finished drywall surface. You can get mud rings in various depths, just get the right ones for the drywall thickness you're using.
Bill
Bill,
I really like these. They are like Tapcons on steroids: https://grkfasteners.ca/product/caliburn-concrete-screw/
Thanks Bill.
Is the main difference of framing as you suggested with 2x3 on the flat vs traditional 2x4 framing the 1.5 inches of saved space? Both options would be against foam board.
If you do traditional framing you have a top plate and a sole plate. The top plate is nailed to the joists above, the sole plate is screwed to the floor. The studs then don't need to fastened to the wall. Fastening tapcons is slow work and the fastener are expensive, this is going to be less work and about the same for materials.
Since this is standard construction anything that follows -- electrical, hanging cabinets, installing trim -- is going to be simpler.
Rather than using 2.5" foam you can drop down to 1" and put unfaced fiberglass batts between the studs. This further reduces the cost and also the total thickness of the wall. Many codes will allow just the fiberglass but I wouldn't recommend not having a layer of foam.
Putting in tapcons goes fast. Use a small rotary hammer and a good bit (that last part is key), drill through the wood, insulation, and masonry. Then put the tapcon in, use a "star" (torx) drive tapcon with a drill that has the clutch enabled. This is how I do it. I use a small Bosch rotary hammer with an SDS plus bit that is the right size for the tapcon I'm using. Those bits are a LOT better than the cheapie bits that you sometimes get with the tapcons. SDS type bits also don't have chucks that get loose while drilling holes, which is another advantage.
Using the right tools to put the tapcons in makes a huge difference and is going to go faster than fully framing a wall I think. Electrical in the "tapcon wall" is just as easy as in a regular wall if you use the boxes I mentioned and mudrings. Trimwork is about the same too. Hanging cabinets I can see being trickier, since you will need to be more careful about where you secure things, and plumbing is limited since a drain-size pipe won't fit. There are always going to be some tradeoffs.
BTW, I personally never use batts in basement walls. I think batts are asking for trouble, even with rigid foam.
Bill
"You are supposed to have 1" of the fastener in the wood. "
Then why is the standard drywall screw for 1/2" drywall 1-1/4"?
I've always deferred to Myron Ferguson for anything drywall:
https://www.jlconline.com/training-the-trades/drywall-hanging-101_o
I bought his paperback 'Drywall' book twenty years ago and still pull it out on occasion. Anyway - he goes with 5/8" minimum penetration, and uses 1-1/4" screws for 1/2" gyp.
True, standard for drywall is a bit less -- 3/4". Presumably because you use lots of screws. 1/2" depth with a drywall screw is probably only around 1/4" or a little more of the actual threads in the wood though, since the point itself doesn't really help much with pullout. My point is still that 1/2" depth in the framing isn't really enough.
Bill
One of my personal failures is getting down to worrying about inches in floor plans
That said, it drives me wild to see full stud walls built in front of concrete basement walls
A stud wall can hold the house up, there must be a better way.
Sure it makes wiring easy, but I cannot see building a wall for wires.
In an old school 24 foot deep house, upstairs you have room for two rooms 11'5 inches after the walls. Downstairs with a 10 inch concrete foundation and insulation and walls you are down to a pair of 10'6 rooms
Man there has got to be a better way.
Just the waste of quality lumber.....