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Rebuilding Sub-Floor in Flat Sitting on Concrete Slab

Postby SuburbanSir » Sat Jan 12, 2019 12:51 am

Currently the living room floor in my flat consists of 40mm wooden joists resting on a concrete slab and 18mm floorboards on the joists. There's a bit of fibreglass under the joists so the total from the concrete to the top of the floorboards is 61mm.

In order to soundproof I plan to remove the floorboards and joists, lay 20mm thick 50x50mm rubber pads like these at 400mm centres (total of 108 for my 12m2 room) with two layers of 18mm OSB at right angles to each other and glued and screwed together.

That only comes to 56mm and I really need a bigger space to fit 25mm rockwool insulation between the pads, so I intend to use some cuts of 9mm OSB slightly larger than the pads to fit underneath them, making the sub-floor 65mm above the concrete. Although this is slightly higher than the existing floor, the adjacent rooms have a 15-19mm layer of ply and vinyl, making them 76-80mm in total, so I'll still have room to fit a further 11-15mm of ply/cork tiles/whatever on top in the living room. I may have to put a layer of 3mm levelling compound on the concrete slab if it's not flat enough though, which will leave me with 8-12mm to play with on top.

My question is whether there's any problem with using square-edge OSB for this or if I need to use T&G OSB or plywood (square-edge or T&G)? As the two layers will be joined, effectively creating a 36mm heavy and dense floor, I wouldn't have thought there was any need to use T&G as there might be when only using one layer (like the existing floorboards) and I fear using T&G just adds the risk of them starting to squeak over time as the wood expands and contracts and the joints starts to rub against each other.

I don't know if plywood is easier to treat than OSB to make it moisture resistant but I wouldn't have thought that was necessary in this case anyway. I note the plywood is somewhat lighter than the OSB, at 22.75kg vs 35kg, which will make it easier to move and work with. ... m/p/110517 ... m/p/120945
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