How best to fix a rotten beam supporting joists

[Tim789]

Hey all

Long story short. I've pulled up my kitchen floor and found most of it in reasonable shape except for this cross beam which is badly rotten. It was encased in damp dirt which explains things. The property was built in 1900 so perhaps this is inevitable.

There is a copper gas pipe right next to it which makes things tricky. Also the brick layer under the beam seems very brittle and I'm sure when I remove the rotten beam the wall will fall apart.

Given all this, my plan (already in action) is to concrete some bricks to the ground (see photos) and create a new foundation layer for the joists to rest on, using solids plastic shims (these) to get the right height. This obviously means the joists will not all be resting on the same beam (which i assume is helpful for stability). I guess I could add blocking/bridging between each joist to 'connect' them. They are all resting on the same beam at the other end of the room which is in good condition so im not touching that.

Is this a bad idea for any reason? I plan to treat the wood with anti rot and cover in DPC membrane before laying down onto the bricks/shims. So it's just about how to ensure a robust foundation layer for the joists to rest on.

 

[StephenStephen]

My amateur response:

-Can you dig more dirt out? I would if you can.
-Is there ventilation? If not can you add some?
-I wouldn't worry about the joists moving - the floorboards will hold them in place.
-I'd be inclined to take out the beam completely, and replace it with a dwarf wall
-You just need a small piece of DPC under the joists (and the beam if you're keeping it) where they sit on brick, don't be covering wood with DPC

 

[Tim789]

My amateur response:

-Can you dig more dirt out? I would if you can.
-Is there ventilation? If not can you add some?
-I wouldn't worry about the joists moving - the floorboards will hold them in place.
-I'd be inclined to take out the beam completely, and replace it with a dwarf wall
-You just need a small piece of DPC under the joists (and the beam if you're keeping it) where they sit on brick, don't be covering wood with DPC

Many thanks, in terms of digging out more dirt, is this to increase airflow? Or to bed in the bricks deeper into the ground?

I will definitely be removing the rotten beam. Replacing the dwarf wall is an option but the gas pipe in the way makes it a bit tricky.

Yep, my plan for DPC was to put a piece between the wood and the brick/concrete. A friend suggested that for the exposed ends of the joists it might be useful to wrap/staple with DPC (i.e. over the final 10-15 cm) to avoid any damage.

 

[StephenStephen]

I dug out a bit deeper to improve airflow, and have the damp ground further from the wood.
You'd wrap the end of the joist if you're putting it in a pocket in the wall, but not if it's just sitting on something.
Other people may be along with more professional advice...

 

[ree]

OP,
I think the suspended floor you show is a replacement floor - the original floor maybe rotted out due to lack of through ventilation. All sub areas should be open to ventilation.
This present joists could go the same way? Probe the joists with a small, sharp screwdriver. Probe deep.
Are there air bricks venting into the floor? Can you post pics showing them on the outside?

Without knowing more about your plans for the kitchen its difficult to say what your best move might be? EG. 1. simply remove the rotted beam, 2. lift the joists in the pics, and re-arrange things 3. there might be further damage to the left of the pics or even think about a poured concrete floor?
The gas pipe needs replacing.
All redundant pipes need removing.
Where timber meets masonry a piece of DPC barrier is needed. Like top right in the pic.

 

[Tim789]

Thanks all, that's helpful. Also I saw that a couple of joist ends have this white stuff on them. Anything to worry about? If not my plan was to scrape away anything loose, sand down slightly and then treat with Sika anti-rot.