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Support structure for xps + osb + hardwood – GreenBuildingAdvisor
I’m building an addition on my house, on top of a concrete slab. The general plan is to use 3.5″ xps, 3/4″ osb, then hardwood flooring. I’m building a frame around the xps with 2×4 pt lumber on edge, anchored to the pillars and the existing house. The entire area being enclosed is about 20′ x 20′. A picture of the patio area is attached.
My question is, do I need to add extra joists / sleepers throughout the subfloor? I’ve heard that just having the xps will make the floor too ‘springy’ and I’m looking for more opinions.
Also, there will be one interior wall in this space. Do I need to add more support under it?
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Replies
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Expert Member MALCOLM TAYLOR | | #1
Dan,
– I would use two layers of OSB or plywood screwed and glued, floating over the EPS, rather than trying to screw down that far or adding sleepers / joists.
– Consider using 15 psi EPS rather than 10 to reduce deflection (springiness) of the subfloor
– As long as the intermediate wall doesn’t take up any loads from above, it’s fine on the new subfloor. -
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Expert Member
MALCOLM TAYLOR | | #3
Dan,
The thickness of the subfloor layers does vary in some of the details I’ve seen, but Randy Williams, Alexandra Baczek and Christi Weber all refer to 3/4″ AdvanTech. I think 5/8″ would be fine, but I’m just guessing.
One thing I left out is that you should start with a layer of poly below the foam to limit moisture from the slab moving upwards into the floor assembly.