Dip in chipboard subfloor - Laying Oak T&G On Top

[Courtyboy]

I have read some of the other threads re: screeds/leveling compounds, etc. However, covering the floor (big room) in ply followed by the self leveling compounds seems pretty epic, and I want to check if it's nessesary.

So in the room I am laying, there is a portion where the chip board has sagged a bit. If I lay a long board then I reckon there's 10mm gap in the middle. This is definately an issue - it will be springy if I don't do something.

However, can I not just pack the problem areas with some ply (or extra underlay) on top of the underlay?

This is a relatively localised problem in a big room (3.73m x 7.62m).

 

[WoodYouLike]

Wouldn't it be better in the long run to find the cause of the sagging?

 

[Courtyboy]

There doesn't seem to be an easy/damage free way to get the chipboard up. It's T&G. I assume the only way to inspect under it would be to cut holes in it.

The sag/dip isn't noticeable until you put a long board down and then you can see it 'bridging'

 

[WoodYouLike]

Perhaps it would be better to check and if needed lift the sagging chipboard out to replace with sheet of plywood?
Then you can install your new wood floor, using foam underlayment (3mm without DPM!) and glue all T&G's.

 

[cmother1]

At the risk of being tarred and feathered here's a quick and dirty solution I've seen done that worked reasonably well. Starting in the middle of the dip cut a hardboard patch to fit the lowest part of the depression. Cut 2 more similar shaped patches increasing in size each time to fill the dent upwards and outwards. Chamfer edges of patches for a better fit and fine tune with Cornflake box or the like. It will still leave some gaps, but if you're using oak it should be strong enough to bridge them. There's no substitute really, though, for pulling the floor up.

 

[JohnD]

Chipboard is an awful material for floors. Quite likely you have a broken bit, either where someoine has jumped on it or stood heavily, or where a short joint is unsupported by a joist or noggin. If you are going to cover it with nice floor you should at least cut that section out and investigate it, renew it if damaged but check you have not got joist problems. If it was me I would rip the lot up and throw it in the skip. Replace with something better, either hardwood floorboards or ply sheets.