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Carpentry & Joinery

Uneven floor, how do i level before putting new plywood subfloor?

What is the best practice to level floor cross 3 rooms and hallway on a first floor of house in a proper and durable way?

I.e. (Joists sistering, or adding patches on top of joist before laying plywood etc..)

Also would I need a structural Engineer to check why floor has sagged?

5 Answers from MyBuilder Carpenters & Joiners

Best Answer

I would attach new joist to side of existing but level and even then lay new floorboards. Further investigation would be needed to see why it is sagging.


Answered 7th Jul 2019

You could plywood the whole area, then use leveling compound. It would need looked at, to see if anything underneath has been removed, and is causing it to sag.


Answered 7th Jul 2019

i wouldfirst find out why its sagging and when thats been attended to i would then level off the top of the joists by using a laser and cutting firring pieces to suit much cheaper option than new joists


Answered 8th Jul 2019

I have had to do this before. Fixed new joists to the existing starting off at the highest point and level away from there, always using that as a datum point.
New 22mm chipboard flooring glued and screwed down.
Also speak to a structural engineer and find out why it has sagged/ dropped


Answered 12th Jul 2019

You need to find out why it has sagged really otherwise your new level floor may sag as well. Firing pieces and ply is prob cheapest way. You could just ply it and then use self levelling latex but this will cause problems if access is needed to floor in future


Answered 19th Jul 2019

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