Hi all,
Unventilated void under stairs, in the pic, causing problems in the hallway.

Interested in thoughts on what to do about it.

Thanks

Had a similar damp, under stairs coal hole here. Right in the middle of the house. Was always damp in there, with just flags on earth. Fotunately, there was a suspended floor with good ventilation the other side of the stone wall, which being an internal, joist supporting wall was "only" 12-18" thick. Dug down as deep as the wall base stones and knocked/cored some vent paths through to the suspended floor.

Then built a raised, insulated, sealed suspended floor over the hole. Not the best energy performance wise but has made the under the stairs dry and usable and, hopefully slowed the stairs from rotting away.

If there were a potential vent path somewhere, maybe a similar option might be viable for you.

Even if your "4th" wall did lead to a vented floor void, with no cross flow of air, tapping into it probably wouldn't do a lot. You could try running a dehumidifier, but that sounds like a hiding to nothing.

If you think the rest of the house can cope with the extra moisture burned, ventilation to indoors somewhere could improve things, but with such a pokey corner, I suspect to get meaningful improvements, you'd have to force the ventilation with a fan.

With that in mind, considering the current weather, you could stick a desk fan in there now and open windows.

If you accept it's damp and that's how it is, sympathetic materials might help. I've found insulating lime based render to be a great moisture buffer. It's not a particularly fantastic insulator but it's capacity to absorb and release moisture is incredible. Digging down as far as you reasonably can (without potentially disturbing footings) and replacing (soil?) With gravel or foam glass also feels like a sensible thing to do, though I can't argue why.

Thanks for the replies. Apologies for the delay. I keep forgetting that this forum doesn't have notifications - so used to other forums where if I don't get an email there is no reply!

Posted By: philedgeIf theres damp rising up through the walls, have you got damp problems in the walls the other side of the coal store?

This is a difficult one to be sure of. The skirting board in the hall on the other side has rotted, but its rotted right along that corner of the hall, not just the part on the other side of the cupboard, so it could be the skirting has been fitted to touch the solid floor there and has been sucking up moisture for years. You would think that with 95% RH inside the cupboard it would have to be working its way through the walls, but apart from a little bit of lifting of the lining paper at the bottom, near the skirting, there are no major problems - no mould or visible dampness.

Posted By: Gareth JEven if your "4th" wall did lead to a vented floor void, with no cross flow of air, tapping into it probably wouldn't do a lot. You could try running a dehumidifier, but that sounds like a hiding to nothing.

If you think the rest of the house can cope with the extra moisture burned, ventilation to indoors somewhere could improve things, but with such a pokey corner, I suspect to get meaningful improvements, you'd have to force the ventilation with a fan.

I have run a humidified in there before, but its feels like just circulating bad air, and as soon as you remove it then its back to the way it was fairly soon. If ventilating to indoors I could reopen the old coal shute as a vent low down and create another one higher up. The top vent would have a very high and spacious hall and upstairs landing to vent to, so it might cope.

Posted By: Gareth J
If you accept it's damp and that's how it is, sympathetic materials might help. I've found insulating lime based render to be a great moisture buffer. It's not a particularly fantastic insulator but it's capacity to absorb and release moisture is incredible.

I had considered lime render, but I think that the idea of a buffer only works if there is a release cycle, otherwise it will probably only improve things until it reaches saturation point.

Posted By: philedgeIf you want to test if a membrane will fix the problem lay a membrane over the top of the existing floor weighed down with dry sand and see if the coal store dries out. Fold the membrane in the corners so its tight against the walls and pile sand against the perimeter of the membrane to keep it as tight against the wall as you can

This could be a good idea, possibly even combined with some venting to the hall way. If it works I could try fitting foam glass or even just some XPS.