Suspended floor repair – rotten edge

[VoidVoyager]

Hi all,

I'm after a bit of advice on how best to tackle repairing a rotten section under the suspended timber floor of my late-1800s stone house in Scotland (photos attached).

It started off with a small damp patch on one floorboard next to an an internal wall (stair void behind ) . After lifting some boards, I discovered a bit of a mess underneath. There was a timber running parallel to the wall, acting as a kind of edge bearer for the floorboards, which was just lying on rubble and dust at one end. This piece was damp and fragile. The main joists run into the external wall on one side.

I've now removed the rotten timber board and cleared away most of the loose rubble, leaving very little support for the new treated timber I've bought to replace it. I'm wondering how best to rebuild support at the corner (shown in photos), where previously it was just rubble piled up. Would it be fine to just use some old bricks and slate?

Also, would it be advisable to put down a strip of DPC plastic between the stone and the new timber?

Another issue is the joist right next to this area, which has suffered rot along roughly the lower half due to prolonged damp contact. It's partly supported by another joist running alongside it but not all the way.I'm looking for recommendations on how best to reinforce or repair this joist given the limited space available. The floor feels quite solid so im not sure if I could maybe leave it as is.

Thanks very much in advance for any advice!

 

[VoidVoyager]

Behind wall

 

[fernicarry]

Are pictures in the second post other side of the wall from the first?

Looks like that slim timber you have removed was sitting on the footings of the brick wall. How did that get wet enough to rot out if its internal? My first reaction was that the rubble was the remains of a fire hearth but unlikely unless its an external wall.

Basically as you said you need to build up from something solid with stone or brick to get to the level you need to support the joists.

Lengthwise along the wall footing it might just be a case of building back support with a layer of lime mortar. Remove anything loose first and give it a really good damping down over several days. Add packers under the new timber as needed and isolate with DPC.

To the right it looks like there is a sleeper wall carrying the full height joists so I'd try to build off of that rather than reusing the previous arrangement in the corner of bricks and slates. The sleeper wall is going to be more stable over time than a pile of bricks.

The rotted timber in your first picture is going to need sistered. Is the piece running to the right still sound? I'd hazard a guess its not given how far gone its neighbour is. Bit awkward due to the overlap between them. Probably going to need to cut back both existing pieces, then bolt a repair onto each to overlap in the middle then bolt the two repairs together. Ideally you want an overlap of at least 18" between all sections.

If you are worried about movement when cutting away the existing joists then stick a car jack underneath.

Not sure what to make of the area under the stairs. The timber looks newish but its wet. Have you addressed the root cause?

Where in Scotland are you?