Rotten suspended floor replacement

[helicopterred]

Hi any advice on replacing the joists that are embedded in the walls, one is an inside wall and the other goes into the inner wall of a poorly constructed cavity, house was built in 1938 and there is lots of mortar droppings in it

The main question is is there anything else i should do whilst the floor is up?
Any easy way of getting the new joists in? the joist in the next room run the other way so i can only push them up to them so the wall thickness plus about 20mm
Should i use a hanger or replace as before
Any specially timber to use is it a structural wood?
The soil underneath feels damp, i have just plastered but i think its generally damp
The joists have rotted with what appears to be damp rot and the floorboards appear to have woodworm or something too

I should stress time is of essence as i have not had a kitchen for a long time now, so i dont want to concrete due to drying time!

Appreciate your thoughts oppinions

 

[Doggit]

You don't replace the whole joist, just the joist end. You'll need to widen the hole that the joist is in, then wedge up the joist from underneath, and cut away the rotted part. You want a replacement piece of joist in tantalised timber, at least 1.5M longer then the damaged part. You place the new joist alongside the old one, and use a couple of clamps to hold it in place. The next part is the tricky bit, you need to drill through both joists, ideally horizontally. I have an angled drill, and I use stubby drills. You need to use 3 coach bolts (no for each new joist piece, that are long enough to go through both joists, and then put a flat plate washer on the nut end, and then put the nut on, and tighten it up. Having wedged up the joist before you started the job, then the joist should stay level, and you check with a spirit level to the adjoining joists. You want to put a piece of plastic DPM underneath the joist end where it sits in the wall, and obviously, you've got to find out why the joist rotted in the first place. Was there earth up the wall inside, or is the ground too high on the outside.

If there's evidence of woodworm, is it old, or is there fresh wood dust around the holes. If you want to play safe, then get some woodworm treatment, a cheap pressure sprayer, and lift every 3rd or fourth floorboard, and spray from each side underneath each lifted board, then on top of the boards, not forgetting both sides of the boards that you've taken up.

It's not a difficult job by any means, so best of luck.

 

[helicopterred]

Hi thanks for the reply however I should of made it clear that all the joists have been removed
The outer wall ends are rotten (Originally a sink there too before we lived there not sure if that contributed)
The rest of the joists are woodworm not as bad as the floorboards and a few of the joists are rotten and crumbling up to a metre from the wall
So basically I have a pit with a sleeper wall in the middle! I guess that changes things slightly
Cheers

 

[John D v2.0]

If the ends are chronically damp due to issues with the wall, you should really solve the wall issue first or keep the wood away from the wall. Consider digging the over site a little and building a foundation for a sleeper wall to keep the timber away from the damp.
Also check the ventilation under the floor to make sure things can dry out.

 

[helicopterred]

Hi thanks for the reply I wouldn't say it was chronically damp and the inner wall certainly didn't feel damp there is certainly rot of some type I would hazard a guess and say damp rot there was lots of soil build up along the wall under the floor but not what I would of thought was excessive
There is only one air brick under the floor which is the size of 2 bricks on top of each other so there is no cross ventilation as such but the rest of the house isn't sealed from this room as all the walls below floor level are honey combed
There is a gulley type drain that is against the wall in that area which will no longer be used when kitchen is finished so I wonder if that's the culprit? It has flooded a few times when it has been blocked with leafs and is in the correct area
Anyway I have decided to buy 3 metre treated C16 cut in half then bolted together over the sleeper wall does this sound ok
Also should I cover over the soil over site which anything or leave it as it is
Cheers

 

[John D v2.0]

In theory you're supposed to cover the over site but it's probably not worth it if it's fairly dry. You're just needing to reduce the sources of water so they dry quicker then they accumulate, not go for perfection.
Personally I'd focus on the ventilation instead as it's a lot easier to add a few air bricks. Go for say one every 2 metres on two opposing walls and get a draught going through, then things should dry out as quickly as they get damp. Hope that helps!

 

[chappers]

As above and yes that's fine to split the lengths over the sleeper wall, also best to wrap the ends that are inserted into the wall in DPM, first I would remove some of the soil build up and there would be no harm in laying a DPM over the soil as suggested, together with some more airbricks . as also suggested try and get some cross flow if possible

 

[helicopterred]

I thought I had a better picture this is after removing 6 bags of soil rubbish etc.
The walls have been plastered so that's why they appear damp but the area with the most serious rot is on the right if you look you can just make out a damp patch next to a bit of green expanded foam
This is exactly where the drain is on the outside wall, it was a bit built up with soil there
Also just remembered this is directly below a upvc window now bricked up
Could also be my liberal use of the hose pipe in there too disguising what is just dry rot and woodworm making it look like damp rot as there is a large ish hole there were the water pipe comes in?
Who knows! thanks for all the above advice I will do the best I can in the short time I have

 

[chappers]

your plan sounds fine just wrap the joist ends and fix together and sit on DPM at the sleeper wall overlap. As said previously maybe consider laying some DPM on the floor. Then when you have more time consider getting some more air bricks around the house to increase the ventilation under the floor.

 

[helicopterred]

What are people's thoughts on loft insulation between joists suspended on gardening membrane so it's breathable and any water leakages can drain away? Running out of cash so kingspan/ celotex type is not viable

Also definitely going to add another air brick when done
Just been rummaging around with my hands in the slot the joist sit in and on the Ines that felt damp inside the internal wall there is a build up of debris I have removed as much as I physically can which is not much but where the joists go into the wall the debris is now below the bottom of the joist level so hopefully this will help
Where the air brick is is damp inside the cavity but this is located right by the drain so may be worse now as I have been washing all my plastering tools there and have been throwing the water in that direction without a thought so hopefully not as bad as it seems! However I have done the best I can with the access I have
Cheers

 

[vinn]

You appear to have a timber plate that the joists are sitting on - completely remove the plate and dont replace it/them unless you wrap the replacement in a fold of DPM material to prevent contact with the brickwork.
Make a hole(s) in the brickwork & open the cavity and clean it out to at least below the joists/plate.
Make good the hole(s).
Lay a DPM across the whole floor.
Honeycomb the sleeper wall.
Install two 10 x 6 plastic air bricks in the outer wall.

FWIW:
Your water supply appears to be a 1/2" lead pipe? If so its unhealthy and too small. Or is it a copper pipe?
If redundant, then abandon the gulley and drain by uprooting to the man hole or removing the gulley and filling the drain pipe with semi-dry concrete at the manhole end and at the gulley end, it will stop rats nesting there.

 

[Doggit]

Make sure you've got a good airflow on both sides of the wall. You're idea of cutting the joist in half is reasonable, but you still want to overlap them in the middle by about half a metre, using a couple of bolts - this'll stop any twisting and rotation.

Beyond that, all other comments posted here are reasonable ideas to follow.

 

[helicopterred]

Again thanks for the comments
The new joists are 1.6metres each side and the room is 2.2metres so there will be approximately .5metre overlap
Some joists are still in place in the picture, they do run left to right and only sit on bricks which are engineering in the outside wall, I do have some DPM somewhere so will use
Only one wall is external so cannot add to opposite side

Have requested a water pipe replacement but as everything else on this project it's a major task as it runs next to power cables sewer and gas pipe in a 1metre wide side entrance and is all shared with my neighbour as it all goes to her 1 metre side passage from mine, and of course it is concrete the whole way to the front! so will get done but not now, to many other things going on

Will the insulation be ok or make matters worse there will be no water over it anymore and once the water pipe has gone can be completely sealed, just that a heated floor is going in on concrete backer boards above it so I thought a bit more under neath would help?
Cheers

 

[Doggit]

Everything you're going to do looks good, apart from the insulation. As you're going to have a heated floor, and I assume it'll be electric, in which case you want the insulation under the backer boards, not under the floorboards - actually, this applies whatever the heat source is really. How are you doing the construction of the heating system; floorboards, ply, then backerboards?

 

[helicopterred]

Oh i was insulating thinking it would reduce the heat loss mainly
Chipboard is going down
Then concrete insulated backer boards
Heat mat
Leveling compound screed
Karndean

Joist are all done levelled packed etc. i cannot find my phone, had it first thing this morning, so will stop for the day and insulate or not insulate tomorrow
As i say the insulation was just to improve heat loss and seal up the top from the bottom if that makes sense?
Cheers