Slope in chipboard floor.

[Ben Lomond]

I had a new chipboard subfloor over existing joists done a few months ago. This is a ground floor in an extension, which was built about 35 years ago, adjacent to a main house. I am planning to put a new engineered wood floor over 5mm wood fibre underlay (https://www.wickes.co.uk/Wood-Fibre-Laminate+Wood-Flooring-Underlay---10-03m2-Pack/p/215589). However, I’ve noticed an 8mm drop across two boards. This is shown in pic. 1. This drop is consistent along the chipboard, i.e. if I put another spirit level perpendicular to the one in the photo it is levelled. I already have tiles in adjacent rooms, so I am also limited in height (as per pic.1).

What is the best option to bring the floor to the level before laying engineered wood? I’m considering a few options:

1. Build up a slope with up to three layers of thin 2mm underlay (https://www.screwfix.com/p/diall-acoustic-polyolefin-foam-underlay-20m/4720r) and wood fibre boards on top of that. This means, to the right of the spirit level, there would be two layers of 5mm boards, and a mix of 2mm foam and fibre boards on top where the spirit level is. My favourite option (seems straightforward and also cheapest) but would this give me any issues, such as bouncy floor?

2. Laying plywood over chipboards. I could try and form a slope in plywood before fixing it to compensate for the slope. I would then put 5mm underlay on top of that all over the floor.

3. Laying plywood to the right of spirit level and filling the slope with a self-levelling compound. This is my least favourite option – seems a bit messy (I’m not sure about using compound directly over chipboards) and if anything goes wrong it can be difficult to rectify.

 

[foxhole]

Is the slope is across the entire room?

 

[Ben Lomond]

Yes, it is.

 

[foxhole]

Yes, it is.

Then why level?

 

[Deleted member 174758]

Really if it's flat I'd probably leave well alone. Trying to take out a zero to 8mm slope won't be easy to do with any solid build up materials and you risk creating voids beneath your engineered floor which can lead to creaking. If you really need to level this out a layer of SLC which allows a feather edge would be a far better solution. You really need one of the flooring guys (like @dazlight) to advise on exact product, though

 

[catlad]

In situations like that I have stapled cardboard to the floor first just too even things out, like contours on a map, each one getting bigger until I am relatively happy.

 

[Ben Lomond]

Thank you all for input, sorry for a late response. The slope was across the room, but not along the room. Something like a chute. The engineered wood manufacturer recommends flatness within 3mm per 2m. I had a drop of 8mm.

I ended up using plywood. I bought 3.6mm, 5mm and 9mm plywood and planed as required down to approx. 1mm. I then used 9mm for the rest of the room. This seemed to work. The floor is stable and levelled.

 

[foxhole]

I think you confused flat with level, does not need to be level .

 

[Ben Lomond]

I think you confused flat with level, does not need to be level .

It was level/slope/level (as per this crude profile). For me the entire floor was neither level nor flat but I might be wrong. Either way, my preference is to have flat and level floor, just a personal thing. It’s done now but thanks anyway.

 

[catlad]

Always better to put the preparation work in first.
Look good.

 

[Ben Lomond]

Thank you @catlad .