How do I level my old joists before subfloor, fibre board & tiles go on?

[Dudefinch]

Hi all, bit of background on my house/floor - 1930's detached. Suspended timber floor (100 x 50mm) on either side of a concrete pad which used to hold a wall up and old oven.

I've removed and replaced (with 95x45mm C24) all the joists on the smaller section of the suspended floor as they had woodworm, and checked and treated the other side. I think the woods ok, but trying to work out how to level both sides has got me scratching my head a bit. I've bought some u shims I was going to use on the smaller side, but on the bigger side some joists are 10mm different in height to the next one, and they're wedged into the wall pockets pretty well, so hard to adjust.

I was thinking to use the heavier grey blocks (trimmed down) in between the new joists, mortared in, instead of the old bricks. Was also going to paint the joist ends in black jack to seal them. Also going to whack some noggins in between all joists about 600mm apart for rigidity.

But the first step will be levelling it all, or rather, making it flat. Do I first go and record the heights of all the joists? Do I not worry too much and use self levelling compound over the subfloor (22mm moisture resistant chipboard 2400x600 with NoMorePly 1200x600 6mm sheets on top)? Do I sister the lower joists? Not sure how flat it all needs to be for the eventual tiles to go on top.

Any ideas or process you normally follow would be mighty helpful.

[Nickfromwales]

On these types of floors I just make the original as solid as possible and then install new timbers alongside the originals (sistering). You find the lowest point (use a laser is best) and work from there, screwing the very end of the new timbers alongside the original and then lifting it up to level it to the laser datum.

 

Your new flooring gets fixed to the new timbers, the originals are just used for support. 

[Dudefinch]

Thanks Nick,

 

So -

level them all up to the current highest point, I have a laser I can use

Sister them to the old joists (I guess the new ones could also rest on the low wall and concrete pad with shims)

So I'd probably need to buy another 11 4x2's

 

Not too sure about what you mean by "screw the very end of the new timbers alongside the original".  Do you mean at the external wall end, put them hard up against the wall?  I did look for hangers as well to support them on that wall next to the old ones, but can't really see an option for a sistered 4x2.

 

I guess then the other smaller section of suspended floor would have to match.  What if the wall pockets don't allow the joists to go any higher?  Do I dig the pocket out more?  

[Nickfromwales]

The originals stay put, no need to dig them out, that’s the reason for adding the new timbers alongside.

 

When I say screw at the end, I mean so one end is fixed and the new timber can scissor up and down on that screw eg to allow it to be raised or lowered to meet the laser datum at the far end. Then you fix that new timber there at the end opposite where you screwed it. 
 

You then go back to the first screw you put in and remove it, then you raise that end of the timber to meet the laser datum, then you have a new bit of timber that is perfectly laser levelled both ends. 
 

Screw that along its length then for a permanent fix, and do the same process with the next, and the next.

 

No need to joist hang the ends, just do the noggins as you say and then between those and the boards being glued and screwed down you’ll have no movement. 

[Dudefinch]

Thanks, that makes sense. 

So the laser level is set to the highest point of the existing joists I assume.

 

The only problem I'll have is the very right hand joist against the wall, which has plumbing pipes attached to it.

I guess I could cut the new joist close to it and then restart it after the pipes again.

[Nickfromwales]

1 minute ago, Dudefinch said:

Thanks, that makes sense. 

So the laser level is set to the highest point of the existing joists I assume.

 

The only problem I'll have is the very right hand joist against the wall, which has plumbing pipes attached to it.

I guess I could cut the new joist close to it and then restart it after the pipes again.

Yes, set the laser to the current highest point.

 

As for the pipes, these just add to the fun!  You’ll be an expert by the time it’s all done 👍. 
 

You can use either side of the existing joist to make life easier. OCD not required here. 

[Dudefinch]

Cheers mate!  Now, I better order a sh*t load more timber!

[Spinny]

Photo from when ours were done in case it helps.

Took them 4 goes and a visit from the structural engineer. 

[Mr Punter]

Are we too late to suggest getting rid of the timber floors and replacing with an insulated concrete floor with UFH?

[Dudefinch]

4 hours ago, Spinny said:

Photo from when ours were done in case it helps.

Took them 4 goes and a visit from the structural engineer. 

That does help to visualize, thanks

[Dudefinch]

3 hours ago, Mr Punter said:

Are we too late to suggest getting rid of the timber floors and replacing with an insulated concrete floor with UFH?

Well...maybe.

A mate also suggested a concrete floor, but funds are quite low now, and I've already bought the 22mm boards and concrete fibre boards.

There would be about a 50cm deep, 5m x 4m hole to fill.  I'm not sure if they normally fill the whole hole, or box it out somehow, but wouldn't that be expensive?

 

[Spinny]

You don't need a concrete floor for u/floor heating of course.

That photo I posted above now has underfloor heating. We were going to have a between the joist system but changed to a within the board system from Omnie when the builder cocked up the level of the concrete slab. (Insulation between the joists, 22mm pre routed board with a matching pre routed overboard - about 35mm thick on the joists.)

[Nickfromwales]

9 hours ago, Mr Punter said:

Are we too late to suggest getting rid of the timber floors and replacing with an insulated concrete floor with UFH?

It's never too late.