Green Building Forum - Unventilated void under stone stairs causing problems Tue, 19 Dec 2023 08:31:38 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301703#Comment_301703 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301703#Comment_301703 Tue, 23 May 2023 12:37:53 +0100 Kenny_M Unventilated void under stairs, in the pic, causing problems in the hallway.

Interested in thoughts on what to do about it.

Thanks]]> Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301704#Comment_301704 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301704#Comment_301704 Tue, 23 May 2023 12:50:19 +0100 Kenny_M https://1drv.ms/i/s!AkPpamnXoVTHgZQ802-7DZXjvIbVSg?e=dQWM2b

I originally wrote a much longer post about this, but then it was lost when I tried to submit, so I can add a bit of an explanation.

The void is under a stone stairway in a 200 year old house, at some point it would have probably contained coal and would have been vented to a draughty back hallway. Now with an extension on the back of the house it is completely enclosed, but the floor is a mix of concrete/flag stones about an inch above bare earth.

Problems in other side of wall in hallway. with lining paper peeling and skirting rotting. RH is 95% in the void.

I could try to ventilate, but this would mean reopening what looks like a coal chute into an internal hall on one side, and venting the other side to a toy room, and that might just be transferring the humidity and other nasties into those areas.

Alternatively I line the floor with something impermeable and fill most of the inaccessible parts of the void. Worry here is that the moisture would just start to find its way up the stone wall and out somewhere else.

Any thoughts appreciated - that do not involve knocking the house or extension down! :)]]> Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301709#Comment_301709 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301709#Comment_301709 Wed, 24 May 2023 09:02:06 +0100 Gareth J
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.]]> Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301712#Comment_301712 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301712#Comment_301712 Thu, 25 May 2023 19:41:18 +0100 Kenny_M
I think ventilation would be ideal, rather than try to seal it into the ground, but there is no obvious ventilation route to outside.There are solid floors on 3 sides, and the 4th side has an extension built on to the old wall. I'm not sure of the construction of the extension floor. The fact that its higher than the old part of the house would imply that its raised, but no sign of vents.

If I ventilate it, I think the only way would be to ventilate it into the hallway, which would not be ideal.]]> Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301713#Comment_301713 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301713#Comment_301713 Fri, 26 May 2023 09:41:34 +0100 Gareth J
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.]]> Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301714#Comment_301714 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301714#Comment_301714 Fri, 26 May 2023 09:50:21 +0100 philedge Unventilated void under stone stairs causing problems http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301803#Comment_301803 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17849&Focus=301803#Comment_301803 Sun, 04 Jun 2023 08:49:02 +0100 Kenny_M
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.]]>