I have a suspended floor in my 1960s house. I am going to struggle to get all of the floorboards up and down again to install PIR between the joists and cannot afford to pay for this to be done. Is it possible to do a floating PIR floor at 50mm and then put a 9mm ply on top in order to do glue down LVT flooring? Changing all the doors etc anyways so that isn't a problem. Thanks!
I'm keen to hear others views on this with more experience to share but I'd be concerned about a. The point loading (9mm ply seems pretty thin, surely If you jump on that you'll damage the celotex) and b. Whether having a vapour barrier above your floorboards is likely to cause problems to the floorboards themselves. There is a real need for a product to fix this type of problem as insulating suspended floors is indeed a proper faff Superfoil do a thin product called SFUF which they claim has magical qualities and you could sandwich between some thin battens with (probably) thicker ply on top. But I'm not sure how much I believe the magic. It needs an air gap really also to work Also are you insulating walls same time? Aerogel I guess is out of scope I've done one of our rooms downstairs with 100mm rockwool and then 25mm ply on top. Really pleased. But had all the boards up and replaced joists. If you really can afford to lose 60mm you could always build a kind of frame above the floor to hold the ply above and then insulate gaps. If you had 20mm battens and did 2x layers of 20mm celotex you could batten then counterbatten to minimise cold bridging. Then 18mm ply or boards on top I guess. The problem with celotex and battens though is it is almost impossible to avoid a gap at edges. Need foaming in at least but even then expanding foam cracks/shrinks over time. An advantage of rockwool etc Other forums recommend full fill underneath with EPS beads, but I was never brave enough! Will keep my eye on this post
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