Under-stair cupboard damp/humid

[thias]

Block and beam has been installed over our basement at ground floor level, with a brick wall built to separate the new B&B floored room and what was the access to the basement, now just a cupboard under the stairs. There are a couple of telescopic air vents under the B&B floor as per building regs.

Since the brick wall went up, the under-stair cupboard has felt damp/humid - the UFH pump/manifold is in here so will be kicking out some heat. Initially I just put it down to the wall mortar drying out, so I left the cupboard door open every day to try help with that, but it's been over a week now and the problem still persists. No noticeable leaks/damp spots and it wasn't an obvious problem before the wall went up.

Does anyone have an ideas for what I can do? I was considering knocking out a couple of the wall bricks and replacing them with air bricks to allow through-ventilation but of course that would cause a draught in the cupboard...

 

[JohnD]

does the space have an external wall? you could fit a small, quiet extractor fan. A modern one will run for 100 hours for 17pence. If there is not a source of water, and it is just construction damp, it will, eventually, dry out.

A new or damp wall can take months.

have you looked under the floor for signs of water?

 

[thias]

No external walls, but at the other side of the new brick wall is beam and block which is ventilated so I could fit an extractor/air brick in that wall to increase circulation.

The floor, which look to be tiles direct to soil, is visibly damp. My suspicion is the air vents at the other side of the wall were helping the moisture to evaporate and by putting the wall up we've exacerbated the problem.

I'm considering pulling those up and laying a new slab. I can't decide whether it's worth going to the hassle of hardcore and DPM, or just tanking over the new slab, bringing the DPM/tanking up to the house's (injected) DPC.