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I have a 35 year old 18mm softwood floor raised on top of 3cm tall sleepers on a prefab concrete floor (insulated in the crawlspace by about 8cm EPS). I'd like to replace it with a new floor but I'd like the floor level to roughly match the old floor.

I suppose an engineered hardwood floor can be laid on top of the existing sleepers (or can it???) but I'm not sure budget allows for this option. Instead I could opt for PVC or laminate flooring but then it becomes a question of how to raise the floor height to 4-5cm (but not higher!)

I could put 7mm isoboard (wood fibre board), 18mm OSB or underlayment, another 7mm isoboard and top it off with PVC or laminate flooring for a total of about 4cm. However I'm worried there will be too soft to walk on. Instead I could do 2cm sleepers, underlayment, and then isoboard and laminate.

What would be the usual way to go about this?

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  • What kind of flooring are you planning on putting down? That's going to determine the subfloor you must lay down under it. Once you know that, the rest is a matter of filling in the height with sleepers (or "joists" as you called them), insulating between them if desired, or just adding another layer of solid flooring if it's not too thick.
    – FreeMan
    Commented Nov 28, 2022 at 17:52
  • "Isoboard" is Netherlands wood fibre board or South African expanded polystyrene?
    – Jasen
    Commented Nov 29, 2022 at 0:46
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    @Jasen The former. No idea how to translate all these products...
    – Sanchises
    Commented Nov 29, 2022 at 5:42
  • Links to product description pages would help, even if they're not in English.
    – FreeMan
    Commented Nov 29, 2022 at 13:12

1 Answer 1

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Since you have not mentioned any major failure of the existing floor, any of the thin floor options are best served by "put on top of the old floor" (which is roughly the same level for thin materials on top) or rent a big honking floor sander and grind off the thickness of the new flooring if you're going to be picky about exactly the same level, even though you say roughly the same.

There are many "usual" ways. If the floor below is cold/exposed, then 2.5-3.5 cm of a rigid foam insulation and 1.5 cm plywood over that works, for adequately firm insulation. The plywood layer spreads point loads and the foams are available in various compressive strengths which can easily be suitable for any usual floor loading (the low end is something like 172 kPa, and 4 times that is easily orderable.)

Recreating a structure like you had, but with insulation in between the joists is also common.The insulation value will be lower due to the wood joist parts, and with modern foam insulation the wood joist parts offer few benefits for almost all uses of the floor.

If the floor below is not cold, pouring additional concrete or self-leveling "compound" is typical - especially for ceramic tile installations.

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  • Oops, forgot to mention that the floor cannot be higher. Laminate wood flooring here is roughly 8mm, is that feasible to sand down? Floor is insulated in the crawlspace by about 7cm EPS.
    – Sanchises
    Commented Nov 28, 2022 at 19:20
  • Used 2cm XPS with 18mm OSB on top. Worked an absolute treat. Thanks!
    – Sanchises
    Commented Jan 6, 2023 at 21:00

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