Replacing entire ground floor suspended timber floor

[Ian H]

Long time no see

My daughters house had a springy floor so we suspected the joists to be rotten.

They are very rotten so we have ripped them out and are left with this:

The old timber was 4.75x2.75” and balanced on broken brick pieces, no DPC at all. I plan to put back in 6x2 on a 4” dpc and level them with slate where required.

I thought if I get the front and back ones in level then run a string line for the rest, that would be best?

The ends and centre will sit on small walls either side rather than sitting in the walls, that’s not too clear on the pictures. So only gravity and their own weight is holding them, because of that I was thinking of bricking up in between the new joists. Does that sound a good idea and if so would you wrap the joists with DPC where they will touch the bricks/mortar?

And finally, should we be looking to put some kind of treatment down there? We have removed a load of rubble and silt/soil and are left with a clean concrete floor.

Thanks

 

[blup]

The suspended floor in our 1930's house sits on sleeper walls, the ends do not sit in pockets in the walls. The floor is rock solid but that is probably helped by the original floorboards crossing the joists at right angles.

In terms of treatment, are you thinking of adding insulation underneath, and how to fix this?

Blup

 

[Andydevon]

Looking at underfloor airflow with airbricks and adding in if necessary would be imperative. Hard to see from the photo but looks to be one just to the rght of you daughter? If its just the one then that not adequate. If you use sleeper walls make sure they aren't solid and block the air flow.

 

[^woody^]

No wonder. Looks like potatoe wood that has started to sprout

 

[Ian H]

The suspended floor in our 1930's house sits on sleeper walls, the ends do not sit in pockets in the walls. The floor is rock solid but that is probably helped by the original floorboards crossing the joists at right angles.

In terms of treatment, are you thinking of adding insulation underneath, and how to fix this?

Blup

She might add celotex type stuff and I would fix that tight to the underside of the floor with some slate lat. Is that how you would do it?

Looking at underfloor airflow with airbricks and adding in if necessary would be imperative. Hard to see from the photo but looks to be one just to the rght of you daughter? If its just the one then that not adequate. If you use sleeper walls make sure they aren't solid and block the air flow.

There are a few on the outside that were all blocked up with silicone. The house flooded about 15 years ago, during a massive downpour and all the road gullys being blocked. There’s a pump with float switch just inside the front door.

I’ll make sure we clean out all the air brick holes inside and out

 

[Ian H]

No wonder. Looks like potatoe wood that has started to sprout

Yes, there is some weird root stuff growing on it There’s a Willow Tree in the garden that needs to come down.

 

[blup]

She might add celotex type stuff and I would fix that tight to the underside of the floor with some slate lat. Is that how you would do it?

I'd probably stuff it between the joists , yes.

Blup

 

[Mr Chibs]

I insulated mine with rock wool, 175mm.
I used mesh as the carrier Stapled to the underside of the joists. It was a lot cheaper than celotex.

It is half as Effective though.

Also, I added a building paper layer before laying the floorboards.

good luck

 

[catlad]

Get a big can of wood preserver if you don't want to be doing it again in 10yrs.
Bits of old lead and slate is perfect for levelling floors.

 

[JohnD]

Get a big can of wood preserver if you don't want to be doing it again in 10yrs.
Bits of old lead and slate is perfect for levelling floors.

I haven't ever had a subfloor void that flooded, but for timbers at risk of getting damp, I stand the cut ends in a spirit-based wood preserver so it soaks in. my preference is to use a steel socket set in concrete to isolate the timber from damp, e.g. corner posts of a shed.

Cuprinol Green used to be effective for timber in ground contact, but is no longer available. I presume because the poisons could contaminate the environment.

If you think the subfloor might ever flood again, I think you should include some trapdoors, and crawl spaces in the dwarf walls. If a trap is in a corner of the room well away from doors and windows it will not get much foot traffic, which avoids squeaking.

 

[mrrusty]

I find the best way to level a surface is to use a laser level and lots of little blocks - lego works well because you can use the different colours to set the line, but wood with a pencil line is just as good. Setting the blocks across the floor they all get scanned by the laser at the same time and you can instantly see the high and low points. Good way for kitchen cabinet tops too.

laser levels for internal are cheap. This is good for a cheapy https://www.screwfix.com/p/bosch-quigo-red-self-levelling-cross-line-laser-level/4708x - got my money's worth out of mine - fine inside, useless outside.

 

[kingandy2nd]

Why has your daughter stashed so much pva glue?!

 

[Ian H]

Why has your daughter stashed so much pva glue?!

I think the plasterer told her to get 5l and she got 5 tubs

 

[jeds]

Did virtually the same job in my daughters last house a couple of years ago. I would invest in a pack of wood shims off ebay or Amazon. I cut my own when I did our job but it is a pain to get them nice and slim. A pack will cost about six or seven quid for 24. Dab them in (folding wedge style) with a bit of that PVA.