Using 2x2s as basement subfloor joists?

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Old 12-04-20, 11:01 AM
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Using 2x2s as basement subfloor joists?

I have very little headroom to work with in this basement, sitting at 7' exactly from slab to the ground floor joists. The floor slab has some small low spots, where several floor drains were at one point. All but one are non-functional, and the floor is overall level. I admit, I don't want to have to get the slab pristine to install flooring directly on it, and would like the extra room for more below-grade safe insulation, so I want to build a subfloor. I want it to be resistant to warping, but I don't want to use 2x4s due to the limited height. Has anyone used these? I know how I want to improve to r-rating and keep 'er dry, just not sure how prone this setup would be to warp. I live in Columbus, OH for an idea of the climate.
 
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Old 12-04-20, 11:29 AM
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What is the sub floor going to do for you?

If carpet they make insulating pads for concrete, we love ours!
 
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Old 12-04-20, 12:37 PM
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I want to install laminate flooring, have a little extra air space underneath it for moisture management, and not have to completely level those small low spots to lay flooring directly over top. I haven't done a basement subfloor myself, but I have seen a couple homes that used a framed subfloor, and in cases where there were low spots in the slab. Even This Old House discusses different basement floor options on their website, and that includes a framed subfloor for some minorly uneven slabs, but doesn't say about the recommended dimensions.
 
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Old 12-04-20, 12:51 PM
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Correction, Bob Vila used 2x4s 16" on center in the example.
 
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Old 12-04-20, 01:35 PM
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Basement 2x2

First, calling the 2x2s or 2x4s “floor joists” is a stretch, and neither will prevent the floor from “warping” if they have to span any significant “low spots”. These would more properly be called “Furring Strips” as they are just creating a flat surface on which you can install a floor. To properly support the ¾” plywood or flakeboard subfloor, which is the minimum thickness you should use, you can use 2x2s. However, they need to be shimmed close to continuously along their length and affixed firmly to the concrete. A good quality construction adhesive for wood to concrete, and concrete screws or anchors every 2-3 feet would be a LOT of work, but would result in a Cadillac and solid installation. Shooting nails into the concrete won’t really work here as they are more for lateral loads than pull out loads. With the load of the subfloor and the furniture on top of the floor, a 4 foot spacing for the screws or anchors could possibly be acceptable. Just be sure that the shims are pretty much continuous along the length of the furring strips, the adhesive is applied to the top and bottom of the shims, and adhesive fills any voids between the shims. A 16” spacing of the strips should be the minimum.
 
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Old 12-04-20, 03:05 PM
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I would highly recommend LVP, they look a hell of a lot better and impervious to any water/moisture.

You dont need any air gap, a good underlayment will do just fine, you just need to address the high/low spots.
 
 

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