Advice on damp suspended floor

[TomH93]

Hi, I've finally got around to tackling the damp problems in the living room, main issue was a damp chimney breast (paint kept pealing off and what I assume is salt patches) however once stripping back everything I found lots of floorboard rotted which at the edges crumble if you push them with your finger. A few joists also have signs of dry rot.



This is a ground floor suspended timber floor and the house is a 1830's stone mid terrace. Looking at the neighbours house, originally the floor would have been stone flags laid straight onto the ground.

I'm now in the process of replacing rotted floor joists and replacing the floorboard's with ply or chipboard while also insulating with wool. I just need some advice that I'm going about this the correct way. At the moment there is no dpm and the joists sit directly onto brick pillars. Usually there is a puddle of water that collects in the middle of the sub floor, which has dried up at the minute. The ground is also covered in mold/salts. Will just fitting a dpm to the joists fix this or is there anything else I need to do?



Also there two vents on the front of the house, however at the back of the house there is a cellar and the sub floor is vented into the cellar, the cellar has been converted into a room and has heating. The cellar is then vented through the old coal shute. Is this an issue having a warm room vented into the sub floor?



Thanks

 

[ree]

There are a number of issues here:
1. all your flues will need sweeping and smoke testing. The stack will need checking out.
2. the odds are that the recess with the elec panel, and the front wall have damp and contaminated plaster. Salt contaminated plaster must be removed, and replaced with a render.
3. you will need maybe three or four 9" x 6" plastic air bricks at the front. More ventilation from the cellar room to the outside would be desirable but without pics of the front and rear elevations its difficult to advise.
4. i think that you will have to honeycomb the knee walls for thro ventilation.
5. previous remedial work has been attempted but failed due to lack of thro ventilation.
6. all fungal infected joisting must be removed. Some joist endtails can be cut back to clean wood, and another length of joist sistered in and capped.
7. new joisting must be capped (like the capped ends you have now) and pre-treated. No new joistwork to touch the brick or stone walls. All joists to sit on strips of DPC material.
8. what do you intend for the hearth?
9. use 18mm (or 22mm) x 2400 x 600 T&G chipboard sub-flooring, screwed down.
10. remove all oversite debris.
11. re-arrange your wiring and cables to run safely. Its convenient to fix outlets at 450mm from the FFL. Have all wiring and piping complete and tested before you fix the chipboards.
12. why not loose lay a membrane (DPM) over the earth oversite? Lap the edges up the walls a few inches.
13. ignore the multi colored salts in the sub-area.

It would help you to read up on similar posts below, and in the search button for this forum and the building forum.

 

[geraldthehamster]

If you have a cellar below that is now a heated room, there may be little point in insulating the floor that you are replacing, in the room above. Floors are usually insulated to isolate a warm space above from a cold space (or cold ground) below, whereas your floor is completely internal.

Cheers
Richard