Replacing joists in a cellar

[RFw3Duwrd7Yu]

I'm renovating an 1880s semi-detached 5BR Victorian house. A bit of reading on the forum has relieved my initial despair after discovering that, in the cellar, the ends of floor joists seem to be in advanced stages of rotting. There is rising damp coming in from external walls, but I'm hoping that the installation of a damp proof course will sort that. However the cellar (which doesn't seem to be susceptible to flooding) has a regularly damp (no standing water) earthen floor which seems to have been wicking up moisture for the past century up the walls into the joists which support the floor of the front sitting room of the ground floor above.

Surveyor and my own subsequent inspection has found that the ends of the joists on the party-wall side (that's the right side in the above photograph) are rotting out. There's also woodworm here and there which hasn't been helping anything. On the opposite (left in the photo) side, joist ends seem to be fine, perhaps because there are regular holes for ventilation.

Sample joist-end close-up above

Another close-up (sub-floor visible in the centre, lath and plaster covering is falling down as shown here, joist to the right)

I had a builder quote me £8k to replace these joists, but am now wondering if I can do this work, carefully and slowly, myself. There aren't any current indications that the floor above is unstable, though I appreciate that this is a job that needs to be done and not saved for later, but this gives me time to set things up and work slowly. I take it that I'll need to get a bunch of Acrow Props to secure the floors overhead and then work in sections across the cellar, replacing beams one at a time. I'm also planning to renovate the cellar, probably installing a damp-proof course, taking out all the stone etc. on the floor and putting in a membrane and floor or just tanking the floor. Main question for now is, is this kind of work DIY feasible? And to others who have done this before, any suggestions about how to set it up and proceed with the work?

 

[cdbe]

If it's just the ends you can splice new timber in. One joist at a time, no need for props.

 

[tel765]

You've got dry rot in the joist tails, the plaster laths, the sub-floor and in between the brickwork. Maybe the dry rot continues through the party wall - have you been in next door's cellar (if they have a cellar) or talked to them?
Maybe the dry rot has climbed up the walls into the room above - examine the skirtings.
Lack of ventilation is probably the main cause.
There's massive amounts of condensation showing. But penetrating and rising damp coming through the walls will also be happening.
Successful tanking would be difficult to achieve.
There could be more dry rot, in the window frame for instance, so go over all the full length of the joists, the woodwork and ceiling laths and plaster probing for rot and softness.

Worst case would be replacing the whole floor, treating with chemicals and adding air bricks and vents.
More info and pics about the ground levels and neighbour's side and the room above the cellar would be needed to advise you further but it might be a job too far for DIY work?

 

[Nige F]

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[Nige F]

I'm renovating an 1880s semi-detached 5BR Victorian house. A bit of reading on the forum has relieved my initial despair ?

 

[Nige F]

You've got dry rot in the joist tails, the plaster laths, the sub-floor and in between the brickwork. Maybe the dry rot continues through the party wall - have you been in next door's cellar (if they have a cellar) or talked to them?
Maybe the dry rot has climbed up the walls into the room above - examine the skirtings.

Has your despair returned . do you trust your surveyor ? or a bloke on the 'net ?

 

[RFw3Duwrd7Yu]

Thanks @tel765 and @cdbe for your insights here. I'm competent at joinery (have planer, various saws, etc) so the idea of replacing wall plate, joists and floorboards isn't too bad. And I'm already planning to take up all the floorboards as the rooms need to be rewired for electric and ethernet and I'm planning to put down some underfloor insulation (probably recycled sheep's wool) and a breatheable membrane, so work of taking up floors was already anticipated. The cellar goes under about 80% of the sitting room, dining room has solid floor underneath as does kitchen (where I'm installing tile and electric underfloor heating).

I agree it seems important to get a more thorough damp inspection (albeit not from someone who will be trying to sell me products after the inspection) and I hadn't thought about needs to engage with neighbour re party wall.

It's my understanding that dry rot feeds on wood and water and will die if I address the dampness, so the brick walls will be mostly intact but plaster will need to be replaced on walls where damaged.
There's no sign of damp in the walls on ground floor on/above party wall and I think it would probably show as they haven't replaced plaster in decades in this house. So, I'm assuming lots of floor work to be done, damp treatments to external walls and cellar floor (I probably won't DIY damp proof course so I can get insurance and guarantee on the work) and replastering to address spots where it has become a problem. Does that sound about right?

Cost wise, I'm ball parking this all at about £1k per room for joists and floorboards as needed + £500-800 for insulation. And then there's the cost of damp proof course and redo of cellar
floor and lower parts of wall, renting a bunch of heater fans, and dragging out rubble from floor. Would be glad to hear
from others who've done this before if this fits your experience.

But my main original question was about the structural elements. It seems to me that this isn't the kind of work that will require input from a structural engineer- but am I missing some possible details? And I'll be replacing timber matched to old originals, so assuming planning approval not an issue.