Timber joist repair in damp cellar

[nero44]

Hello Everybody,

first time poster, be gentle

I've recently moved into a ca.1900 bayfronted victorian house, which has a small (ex coal) cellar. It is accessed under the staircase and runs below the hallway. It's ca 5.5m x 2m and only half height, so one needs to duck/crouch down there. There is currently not any flooring, so the earth/clay the house sits on is fully exposed. I've attached a few pictures to give you an idea of what I am dealing with. I've put down some old wardrobe door panels to walk on to prevent the soil/mud being spread around the house. This cellar was flooded due to a broken pipe in 2021, but this has been fixed since and no further issues.

My issue is that the joist (indicated by the blue arrow) seems to be giving in. I have't noticed any sagging floor and the damage does not look recent, but I suspect it could be from the supporting pillar and the stair case suffering some wet rot as they basically sit almost directly on the damp clay. As the surveyor did not seem worried and I do see any sagging, I am less worried about the structural integrity but more so by the fact that a water and gas copper pipe run underneath it. In case the joist comes lose it might hit the copper pipes.

What would be the recommended course if action here? I would think the joist might need sistering, with possible correction to the sleeper wall. Furthermore, I would be inclined to replace the staircase and the pillar, perhaps with a concrete base or a slab so it is somewhat shielded from the damp soil?

Would this be a job for a carpenter/woodwork or general builder? If anyone has any recommendations of an experienced tradesperson/company serving North London, feel free to share.

 

[a twig]

How long are the joists that are running what I presume is front to back?

 

[Stevers]

The propped timber beam with the junction boxes on it looks like a 'repair' to support that floor. That crosses the staircase awkwardly and I doubt that it's original.

 

[CliffordPope]

It looks a very straightforward DIY job just to replace the joist.
Put a car jack on top of a pile of blocks and lift the joist that is immedately resting on the rotten section, and lift about 1/4 inch. Put wooden posts under the other joists and hammer in wedges enough to take the strain and lift the rotten beam enough to give minimal clearance.
Then with all the weight taken off the rotten beam slide it out and put in a pre-cut replacement. Put in packing pieces if necessary, and then knock out the wedges and lower the jack.

 

[nero44]

Correct the joists run front to back, so really we are looking at the sideways support beams of the joists that have some damage. Some of them further down appear to have been supported already by the previous owner. Will get you some measurements and maybe a rough sketch after work.

The propped timber beam with the junction boxes on it looks like a 'repair' to support that floor. That crosses the staircase awkwardly and I doubt that it's original

Agreed, probably because the decayed one is not firm. I just dont want it to collapse onto the pipes.

As for doing it myself, possible but I work full time and my weekends are mostly packed with other projects in the house I feel more confident doing. This one I’d feel more comfortable paying someone todo this, including putting a concrete base for the stairs. I am attaching a few more pics for colour. The wet rot on the base of the stairs I’ve cleaned and treated with ronseal hardener for now. Also wedged some spare plastic sheets inbetween as temporarty moisture barrier.

 

[nero44]

How long are the joists that are running what I presume is front to back?

So here is a rough sketch. There are 4 joists impacted, each of which is about 6.5m long. On the top side they sit on the foundation and then further down I've indicated the five supporting beams they rest on. S means (s)leeper wall and W is the this makeshift propped timber beam resting on the (w)ooden post. I've also measured the distance between each supporting beam, so that reads (from the bottom) 1.2m / 1.5m / 1.2m / 0.6m and then from that staircase pillar back to the foundation wall measures 1.7m. That staircase pillar is pretty much gone at the bottom from wet rot, but it is attached to the staircase, which rests on a brick. The lower three beams are all extra thick or double supported. I've also noted that the sleeper wall of the second to last beam is just a single brick wall and is slightly slanted. The other ones look quite solid.

What sort of tradesperson should I be contacting? Any recommendations?

 

[Cubist]

At 6.5 meters long even a wide profile timber of greater than 100mm would have a lot of deflection at the mid-point which explains why the sleeper walls and the additional timbers below were installed when the house was built. A good general builder would have all the skills and equipment needed to replace the rotted supporting timbers and sort out any corrective masonry work. He/you may need access to an electrician/plumber/gas fitter depending on what those service pipes may be but again a good builder should have access to these capabilities.

The thing to look out for and ensure is done properly is the making good, and specifically safe, of those stairs into the cellar. Whatever repair work is carried out then ideally any woodwork must be isolated from the damp rising from the cellar floor.