I am repairing an old garage / small barn (24′ x 26′). Downstairs, the owners park their cars on a dirt floor. Upstairs is being converted into a painting studio. The floor was originally 2 courses of rough, random width 1x run perpendicular to the joists. I am going to install 3/4″ A-C Ply as the new finish floor. The 4″ x 8″ joists range from 24″ to 30″ o.c.. I’ve stripped off the top layer of flooring to facilitate leveling the floor, and to remove much of the crap that worked itself in between the two layers.
I’m going to use spray polyurethane foam to insulate the building, but wanting to leave the underside of floor exposed, was thinking of laying 2″ rigid foam on top of the first layer of floor. At first, I thought putting a course of 3/4″ plywood right on top of the rigid foam would work but after talking to DOW about their Tuff-R panels, was told that they weren’t designed to support a floor. And to use sleepers instead.
So, my question is, can I use 2 x 4 sleepers run perpendicular to the joists to support the plywood floor? The sleepers (or strapping, more accurately?) The 2 x 4’s would be on the flat, dropping my rigid insulation down to 1 1/2″, and run 16″ o.c.. Between the widest spaced joists, the 2 x’s would be spanning 28″. Too much? Can/should I strip off the remaining layer of 1x flooring and install the 2×4’s and foam board directly to the joists?
Thanks, Mike
Replies
You aren't seriously going to use AC plywood on a floor, are you ???
The world's full of apathy, but I don't care
Mike,
Is there a beam supported by posts running down the center of the garage? If not that's one heck of a span for a 4 x 8. Using 30lb live and 10lb dead I don't see getting more than a 16' span with really dense wood. We are not talking structural failure, just deflection and cracking to a ceiling finish in the garage. Which by the way, you do plan to apply gypsum board to the ceiling? The insulation board needs to be covered with 1/2" gypsum board.
If you have a center beam you should go with 2 x 4's on top of the joists because 30" is a bit too much for 3/4 plywood to span. The plywood needs to be tongue and groove.
If you don't have a center beam you might consider going 4 x 8's 12"oc. Or to level the floor, place 2 x 12's between the 4 x 8's then scab 2 x 6's to the sides of the 4 x 8's.
Yes, two beams running across the building, breaking up the 24' length into approx. 8' spans for the 4"x8" joists.
If the rigid foam is sandwiched between the existing floor and new plywood, does it still need drywall for fire rating? This is an unattached garage. No sleeping rooms. Just a utilitarian painting studio. I'm not sure of the code. Will look into it.
The building is in New Jersey, will R-14 be enough for a floor? The sloping grade rises to the 2nd Floor level in the back, lessening the cold winter air a bit I'ld think.
Thanks, Mike
From a practical stanpoint it sounds like what you are proposing will work just fine. I actually did that once when I had truss-joists at 24" O.C. and I didn't want to have to lug those heavy ol' sheets of 1-1/4" sturdi-floor around.
I don't know nuttin 'bout no New Jersey building codes, though.