Floor levelling

[Marcos]

I need to lay a wooden floor in the living room of my flat, probably bamboo or oak boards. The current floor needs to be levelled first, due to some subsidence occurred some 30 years ago (the house was underpinned and no further movement has been detected). The problem is that the floor at the middle of the flat is about 3cm (1 1.4") lower than it is at the walls.

I'm looking for the quickest solution and height of the floor is not a problem. Is it possible to simply lay plywood on top of battens placed over the existing floorboards to make the floor level prior to laying the underlay and final bamboo/oak boards?

I thought I'd use 15mm plywood and battens spaced at every 40cm. Would that work? And could I use cheaper chipboard instead?

Thanks for any help!

[TMC]

Just out of curiosity does the floor slope towards the centre from all 4 walls?

It would be possible to cover in plywood or flooring grade chipboard directly to the floorboards around the edges and batten with increasing thickness battens towards the centre if the slope is only from 2 opposing walls Battens could be lengths of ply or chipboard of appropriate thickness for the thinner ones and 50mm wide timber cut to thickness for the thicker ones. Fit on top of the line of the original joists

If the slope is from all 4 walls it would be a bit of a job tapering the underside of the battens as well

Tony

[jack]

use a levelling compound plug any gaps in the boards and fill in the hollow in two or three layers use a long straight edge to check for flatness

[Marcos]

On 13 Jun, 22:57, "TMC" wrote: Thanks for your reply.

There is a little slope between the front and the back, but it is negligible (the front is about 2mm lower than the back). The main slope is between the side walls towards the center.

That's I have in mind. Do I have to worry about how thick the ply or chipboards are? A friend told me 15mm ply should do the trick, but chipboard seems to be much cheaper.

That's a good tip, the joists are separated at every 15" (38cm) (not

40cm, as I was told).

I agree!

[Marcos]

There are two many gaps. Not sure I could use some sort of membrane underneath!

Thanks.

[Rick Hughes]

I think that would not be suitable for on top of wooden boards ..

Use T&G flooring chipboard .. glued on all 4 edges, and as you have suggested tapered battens. Start at highest point and batten parallel to all 4 walls .. then run strings between then .... and you have to plane/cut battens to meet the string.

If you use 25mm thick sheet, and battens at 400 c/s ... it it were me I would glue & screw battens down to joist below - and then glue & screw deck sheets to battens.

However if you need access to any services under the boards then that is a different issue.

[Stuart Noble]

Sounds like a long and painstaking job. I'd go with the levelling compound and straightedge suggestion. The latex version is very adhesive, and I'm sure would bond to wood. This would also keep more or less the same height

[Chris George]

Dear Marcos You do not say if this is a ground floor with an underfloor void and subfloor ventilation or an upper floor. IF it is a ground floor what you are proposing has certain dangers and needs further preparatory work If it is a ground floor the subsidence to which you refer is in the oversite and that is resonably easily accessed by lifting floorboards and raising the wall plate off the sleeper walls with slates and dry pack. Use a bottle jack on the joists. YOU WILL NEED TO ENSURE SUBFLOOR VENTILATION complies with the correct BS or whatever particulary if you are now blocking up any cracks between existing boards. If it is an upper floor it is not settlement but BAD DESIGN or possibly building with wet timber and a "duration of load" effect when drying through the fibre saturation point where you can get great proportional creeps and huge deflections. I think this is unlikely. Upon you advising which it is I can give better advice.

[Marcos]

Dear Chris,

Thank you very much for your message.

The flat is the first floor. When I bought it, the survey mentioned that there was some misalignment probably due to subsidence, but that there were no signs of any recent movement. I also saw somewhere in the paperwork that the house had been underpinned in the early 80s. The windows in the living room are not 100% straight, but there is no noticeable slope matching that of the floor. There are no visible cracks on the exterior wall inside or outside the house (where the bricks are exposed).

I don't believe it was timber settlement, because the slope is perpendicular to the direction of the joists (which are over 8in deep). I believe the house was built around the beginning of the 20th century.

Should I be worried?

Marcos

Chris George wrote:

[Chris George]

You say earlier that "There is a little slope between the front and the back, but it is negligible (the front is about 2mm lower than the back). The main slope is between the side walls towards the center. "

I now know it is on the first floor I assume as you dont say otherwise that the two side walls are level with each other. Ipso facto any "subsidence" is on and partition wall in the midspan on the floor below - which is not uncommon if plonkers take them out or more likely they are not so well founded as the perimeter walls or worse still not founded at all but resting on floor boards of the GF! So two options

1 assume that it is now acceptably founded on settled structural walls below in mid span, all that is needed is to check this (any compentent surveyor) in the flat below and to put on individually shaped firrings on the top of each joist using either a laser level or bit of string or what I would do is to make a hardboard former - you will need help - by putting say three or four marker lines at the level you want - put the hard board up beside the joist in 2400 by say 150 bits and marking out in pencil the exact shape of the bit you need to add on. Lie this up against the timber you are going to use to cut out your batten from and transfer the dimensions to that timber. This will be an exact fit to the joist which will NOT be a straigt line so cannot use a straight timber. Long and time-consuming but that will give you a good job to put back on floor boards. If you are putting on sheet material then you can cross batten much much quicker but make sure it is done at good centres and that you have them accurately marked on the skirtings or you wil have a hellofajob in nailing down! I deal with listed buildings all the time and such floors are not allowed to be levelled without consent as it is all part of the rich tapestry of history of the building so think about whether you actually need a floor to be straight! Chris

[Marcos]

Dear Chris,

Thanks for the very useful > I now know it is on the first floor

I'm not sure I have to check that. There are two floors below mine and I know that the floor below has the same partition wall as mine. I'm not sure about the lower ground flat, as I have never been there. Could the house be in danger?

I was planning to batten above the joists and place the sheets on top of the battens (i think this would be quicker).

My building is not listed and not in a conservation area either. To be honest with you, I'd love to keep the original boards and I don't mind the slope. However, the original boards are in a very bad state and have big gaps - I have restored old boards in the past, and these are the worst I have seen. I'm not keen on carpet either. This is the first reason. The second one is that I had to level other parts of the flat: the kitchen, utility room and bathroom had to be levelled before installation. This created a "step" down the hall and living area. Even if I were to put carpet on top of the existing floor, I couldn't avoid the step and new wood flooring wouldn't go well with the slope, so I can't see an alternative!

Marcos