Sloping floors

[Albie22]

Hi,
I had planned to lay wide plank engineered floorboards in a 9x4.5 kitchen/diner. It was previously a seperate living room and dining room.
The wall between the two rooms has been removed and the extent of the sloping is making me rethink my plans.
From the central point of the room(where the wall was removed) there is 60mm drop to one side of the room and a 45mm drop to the other,
I’m trying to figure out the flex tolerance of engineered boards. Any more knowledgeable people out there have an opinion if this is a frankly terrible idea to continue with?
The floors are flat but sloping. Levelling the floors will take some significant work and replacing joists etc is beyond my budget at the moment.
The other option is to put down something like marmoleum but I’m slightly frozen with indecision and I’ll need to inform the floor fitter soon if I’m going to change my mind!
Thank you!

 

[jamest]

I have found that engineered floors (20 mm thick with 5 or 6 mm oak surface layer) are more tolerant of variations in the subfloor than the manufacturers say. I guess that makes sense - they want to ensure that there no chance the person will come back and claim a refund based on something going wrong. Having said that, I can't answer your question because (1) I don't know what kind of flooring you want to use or what the manufacturer says it will tolerate, (2) the kind of slope you have, (3) the nature of the subfloor.

From your description it sounds as if the floor might be like a double ramp that meet at a peak in the middle and the subfloor is old boards over joists. If we say that the long length of the room runs from front to back and the short length from side to side, I have interpreted you as saying that the sloping runs front to back on either side of where the dividing wall once was. So one ramp runs down towards the front from the wall position and the other runs down to the back. There is no slope side to side. Is that correct? If it is, it's not the slope that's problematic, but the peak in the middle where the wall was. In such a situation with drops of 6 and 5 cm, you'll not be able to run boards long ways (front to back). You could run them side to side but you'd need to put in a bridging piece in the middle where the wall was (maybe a T-profile).

 

[Albie22]

I’ll add a diagram which might help too! The floorboards are 20mm with 7mm wear layer. The joiner has advised to run the short length of we want to stick with floorboards but it doesn’t look great. The boards are 240mm wide and 2200mm long.

 

[jamest]

Looks to be more or less as I thought from your original description. I take it you want to run the new boards front to back as illustrated (lengthways), rather than side to side. That's not going to work as it is as your carpenters have probably told you - they'll not want to run them lengthways because they know that the boards could split. Your only option (other than doing it properly and altering the joists) would be to some how build up the floor to even out the ramps. Leveling compound could work, but over floor boards it will have a limited life. Is there another way? The only thing I could think of is to run strips of wood side to side, the thickest ones (5 and 6 cm thick) next to the wall at each end and then progressively thinner ones as you reach the middle spaced at roughly normal joist spacing (about 40-50 cm or so). These couldn't be very wide (not more than an inch) else they would have to be angled to match the floor slope, that would be tricky to do over a 4.5 metre length.

 

[fernicarry]

If you go lengthwise the difficulty will be fitting the boards together as they pass over the high spot. Particularly if its a click system where you lift the next board up on its edge to angle its tongue down into the groove of the previous run. Unless the previous boards are sitting dead flat its a real battle to get the new one to engage along its length. You might be able to improve your chances by using relatively short boards around the middle of the room and propping up the previous boards temporarily to keep them flat. Depends very much on how sudden the change in slope is but given it was two separate floors I'm guessing its not that blended. Even if you do get the boards to go together they could be bouncy if they don't flex enough to sit down on the subfloor.

As @jamest says by far the easiest solution is to treat as two separate floors. If there is still some evidence of the dividing wall that used to be there then this might not look out of place. Skirting boards are also going to be a problem around the transition so making a feature of where the wall used to be will help with that too.

 

[Albie22]

Thanks both. The original floorboards have been lifted and there’s a caber floor and sheet ply on top.
The house had been a rental for a long time and the botch jobs we are uncovering are certainly testing my patience and bank account!

 

[Cubist]

'Firrings' - a firring is a wedge shaped piece of timber that is installed directly over a joist to level a slope.

Assuming that the underlying joists run at right angles to your indicated/desired floorboard layout then the individual firings would need to be cut to establish a new level between each of the joists - those nearest the low points in the room being 45mm and 60mm respectively and reducing in thickness nearest to the current high spot/line.

Should the joists run parallel to the indicated/desired board layout then each firring could simply be cut to 60mm or 45mm and reduce to zero over the length needed to meet the high-point line.

Any decent joinery store near you could cut these for you.

Oh... and something to be wary of - door thresholds could be compromised and force adjustments to same in some instances.