1. Your past attempt at "tanking" has failed.
Who disturbed the skirtings?
There is a distinct shaded band about 1m high in the south pic. indicating a temp change along that line.
2. The north pic floor/wall footprint is odd - it doesn't match the exterior pic.
3. An access trap might be anywhere in the property GF - from there you crawl the whole sub-floor oversite. If no trap visible, then cut one in an unobtrusive location.
Your joist tails are at fungal risk - crawl the site, and examine all joist seatings - probe with a screwdriver.
4. Vents are req'd every 2m and within 1m (both sides) of a corner. Your hallway is vulnerable. Research vents on here.
5. Sand & Cement plinths in 20thC buildings are often inadequate attempts to deal with damp, or perhaps aesthetic features. Unless they are 18th or 19th c originals they are questionable distinctions
6. Open the man hole and observe for a flush from the WC, and from the side gulley(s). Perhaps the soil drainage runs round the south side and picks up the gulley(s) on it's way to the m/h?
7. Depending on item 6 the sump will have to be led away from the property.
8. Dont cut and channel out 6" of the top step unless you provide a cover/tread (a grill?) for the gap.
Who disturbed the skirtings?
There is a distinct shaded band about 1m high in the south pic. indicating a temp change along that line.
2. The north pic floor/wall footprint is odd - it doesn't match the exterior pic.
3. An access trap might be anywhere in the property GF - from there you crawl the whole sub-floor oversite. If no trap visible, then cut one in an unobtrusive location.
Your joist tails are at fungal risk - crawl the site, and examine all joist seatings - probe with a screwdriver.
4. Vents are req'd every 2m and within 1m (both sides) of a corner. Your hallway is vulnerable. Research vents on here.
5. Sand & Cement plinths in 20thC buildings are often inadequate attempts to deal with damp, or perhaps aesthetic features. Unless they are 18th or 19th c originals they are questionable distinctions
6. Open the man hole and observe for a flush from the WC, and from the side gulley(s). Perhaps the soil drainage runs round the south side and picks up the gulley(s) on it's way to the m/h?
7. Depending on item 6 the sump will have to be led away from the property.
8. Dont cut and channel out 6" of the top step unless you provide a cover/tread (a grill?) for the gap.