Attach subfloor over XPS to concrete with powder driven nails?
albion15
| Posted in Construction Techniques on
There are a couple of related old posts to this but I can’t see an answer to exactly the same question. Appreciate your help
I’m installing T&G subfloor over 2″ XPS over cured concrete. I could go with tapcons but they’re expensive and a bit slow, whereas I’m cheap and lazy – total area 1200 sft. I’d like to use powder driven nails (but have never used them before). It seems to me that the nails will be prone to bend & bounce off the concrete by the time they’ve gone unsupported through 2″ of foam. Maybe I’m daft and this is completely standard, but if someone has actually done it I’d appreciate a green light before I mess it up.
Replies
you'll never get 'em flush.
All else aside, you'll either shoot them throug the plywood or leave them sticking up. Stick with the tapcons.
I agree with Mike. I also wonder if you could just use a floating floor of two lapped layers of 1/2 in. screwed together?
Sigh. Good point about penetration depth. Exactly the kind of advice I needed thanks. I'll stick with tapcons
yes I could screw 1/2" sheets together except I have the 3/4 T&G sheets on site. Sigh again
did not want to leave it free floating because I don't want the subfloor sheets warping up and making a crazy golf surface in the basement
Gravity works!
The only time I could see it being any issue is if you had a dip in the concrete you MIGHT experience the floor flexing when you walk on it. But that is a MIGHT. For the savings in effort, time, money and wear and tear on my body, I would at least start here and then walk around on it. If you should find a spot that flexes then opt to secure it in those locations. Aside from the that, where is the floor going to go? I suppose it could literally float if you got enough water in the basement but in that case not having it attached is an additional benefit not a drawback.
Tapcons are the way to go
I did tapcons for my concrete basement floor, but did 1" of foam (instead of your 2" foam) and 1/4" delta FL dimpled membrane for my 3/4" plywood subfloor (so it went concrete, dimpled membrane, foam, plywood).
My experience was that I had to use the 1/4" tapcons--the smaller 3/16" diameter ones didn't have enough holding power.
Also, you are going to need a SDS hammer drill and you'll need to buy the SDS hammer drill bits (most packages of tapcons include a bit, but it is not an SDS bit). You can use the SDS hammer drill to drill the holes and a standard impact screwdriver to drive the screws. I used a vacuum to suck the dust out of the holes as well.
I believe I had to use 4" screws--the 3 3/4" screws weren't long enough to grab enough concrete to hold. So, you'll likely need to buy 5" tapcons, and you'll have to use the countersink phillips, not the hex version, if you want the floor to be flush (which is too bad since the hex version are far easier to drive).
My other advice would:
1. Consider if your floor is perfectly flat or not. If it isn't, now is the time to use some self-leveling concrete to correct it. Once the plywood is down, that option is lost (sigh).
2. If you have load-bearing walls, you can't pull them on your concrete/foam/plywood sandwich. You need to use pressure treated wood directly onto the concrete, and you can then satisfy your urge to use powder driven nails when installing the PT.
3. And if you are finishing the walls (which is pretty safe to assume), be sure to put up your vertical AND horizontal fireblocking before you put your walls up (and before you apply any sheet foam insulation to the walls). Trust me when I tell you that it is a major pain in the butt to put fireblocking up after the walls are up (sigh). Look at pages 5 + 6 of the following link to see fireblocking details.
http://www.cityofthornton.net/Departments/CityDevelopment/Development/Documents/BUILDING%20INSPECTION/Building%20Guides/2012_Basement_Finish.pdf
The concept of vertical and horizontal fireblocking makes more sense when you realize that the 2x4 stud walls may be set BACK from the actual basement walls for air movement/straightness/room for pipes, etc. The simplest way to do the horizontal fireblocking is to attach it the mudplate (using 6", 8", or 10" 2x lumbers depending on how far out you want the stud wall to be from the basement wall). The fireblocking can then become a useful chalkline of sorts, so you just have to align the bottom plate to it (ask your building inspector if you can use it as a top plate too).
Good luck.
Fireblocking can also be the air barrier
One thing you don't want is air moving from between the framed wall, the foundation wall, and the floor framing. This is for both thermal and moisture control reasons. When you do the fireblocking, take time to seal it with foam or acoustical sealant to fully block the movement.