Naive question about raising floor level

mjgreen81 · 27 Jan 2026

Hi,

I am currently part way through a renovation of a small downstairs WC. I have removed the old floor tiles (which were about 11mm with the adhesive) and will be laying some LVT planks which are only 5mm. I need to make up the remaining 6mm so it doesn't look like a big step down from the adjoining room.

The subfloor is chipboard.

I have never raised a floor level before, is it just as simple as laying down some 6mm plyboard on top of the subfloor? If yes, what is the best way to secure it? I am a little cautious about what pipes may be underneath the subfloor, but at the same time it might be nice to be able to remove the ply in the future if I ever needed to.

The floor is 'L' shaped. Is it ok to have one piece of ply covering the main section of floor and one covering the cut out? If yes, do I need to do anything at the point where the two pieces of ply join?

Thank you

jj4091 · 27 Jan 2026

Easier with this

https://www.diy.com/departments/volden-5mm-wood-fibre-laminate-wood-underlay-panels-6-99m-/5063022038852_BQ.prd?storeId=1070&&&&&gclsrc=aw.ds&gad_source=1&gad_campaignid=21158206276&gclid=Cj0KCQiA4eHLBhCzARIsAJ2NZoJCS7qx60LNNoSlN1tktB8RyiQU25qyFq9Bb_TGJfbG2qhfsPSDmfsaAr-cEALw_wcB

Cheaper at it's sister company S/fix but can't post links on here. You won't notice the slight difference with a threshold bar fitted.

mjgreen81 · 27 Jan 2026

jj4091 said:
Easier with this

https://www.diy.com/departments/volden-5mm-wood-fibre-laminate-wood-underlay-panels-6-99m-/5063022038852_BQ.prd?storeId=1070&&&&&gclsrc=aw.ds&gad_source=1&gad_campaignid=21158206276&gclid=Cj0KCQiA4eHLBhCzARIsAJ2NZoJCS7qx60LNNoSlN1tktB8RyiQU25qyFq9Bb_TGJfbG2qhfsPSDmfsaAr-cEALw_wcB
Cheaper at it's sister company S/fix but can't post links on here

The LVT Click flooring I have specifically says not to use an underlay (this was also re-advised by the shop floor worker when purchasing it)

noseall · 27 Jan 2026

mjgreen81 said:
If yes, what is the best way to secure it?

Short screws.

mjgreen81 · 27 Jan 2026

noseall said:
Short screws.

I was asking for that .

I just wasn't sure if screws just into the chipboard sub floor would be enough and I may need adhesive as well.

What sort of distance apart should the screws be please?

noseall · 27 Jan 2026

mjgreen81 said:
I was asking for that .

I just wasn't sure if screws just into the chipboard sub floor would be enough and I may need adhesive as well.

What sort of distance apart should the screws be please?

About 200mm and in line with the joists. So five or six per 1.2m over every joist or about 40 per 1200 x 2400 sheet. Add a few more if there are hollow spots.

noseall · 27 Jan 2026

mjgreen81 said:
I was asking for that .

I just wasn't sure if screws just into the chipboard sub floor would be enough and I may need adhesive as well.

What sort of distance apart should the screws be please?

Be wary of pipe and cable runs though, if the screw happens to overwind.

mjgreen81 · 27 Jan 2026

noseall said:
Be wary of pipe and cable runs though, if the screw happens to overwind.

I will be as careful as I can be, I have no idea where they are. Will just play it safe and be very cautious when screwing.

What is the normal depth of chipboard flooring in a late 1990s house?

noseall · 27 Jan 2026

mjgreen81 said:
I will be as careful as I can be, I have no idea where they are. Will just play it safe and be very cautious when screwing.

What is the normal depth of chipboard flooring in a late 1990s house?

Assume 18mm

mjgreen81 · 27 Jan 2026

And what about where the plywood joins? Should I use anything to cover the joint?

noseall · 27 Jan 2026

mjgreen81 said:
And what about where the plywood joins? Should I use anything to cover the joint?

It's important that the joints with the flooring above don't clash with the ply. Rather they should bonded or staggered over.

Deleted member 326613 · 2026-02-19T09:58:39+0000

Yes, you’re on the right track, 6mm ply is a common way to build up height over chipboard before laying LVT.

A couple of key points though:

Use flooring grade ply, not standard shuttering ply. You want something smooth and stable, ideally hardwood ply suitable for floor prep.

To fix it down, the usual method is:

Screw it into the chipboard (not glue alone).
Use plenty of screws, roughly every 150mm around edges and 200mm through the middle.
Keep screws flush, not proud.

If you’re worried about pipes underneath, use shorter screws and avoid going too deep. Most pipes should sit below the chipboard, but it’s always wise to double check where possible.

I wouldn’t rely on adhesive alone if you’re laying LVT on top. Movement is the enemy with LVT, so you want that ply solid.

As for the L-shape. yes, that’s absolutely fine. Two pieces is normal. Just:

Leave a small 1–2mm gap between sheets.
Stagger joins if possible.
Lightly sand the join if there’s any lip.

You don’t want a ridge telegraphing through the LVT later.

One last thing, make sure the chipboard underneath is secure first. If there’s any bounce or squeak, fix that before adding ply.

Done properly, 6mm ply will bring you up nicely without creating future issues.

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Naive question about raising floor level

Deleted member 326613

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