Heavy condensation in under stairs cupboard

[houseonahill]

We moved to a 1950s detached house in September which has a cupboard space under the stairs. I've noticed some quite heavy condensation inside it which you can see in the attached pictures. The cupboard does smell faintly damp and there was a lot of mould / blown plaster on the walls here before we had them replastered (back to brick) last month.

Please note: the white stuff is NOT salts or some other powdery residue, it is actually little beads of moisture catching the light of the camera flash. But that gives you an idea of how much moisture there is!

The far wall is exterior and beyond that is our driveway which has been built fairly high though still below the DPC. The cavity (60mm) was recently completely cleared out, both of insulating beads and rubble at the base (and there was plenty of rubble in there). The builder also put a new DPC in the outer leaf and repointed along the first two courses of brick. So I am pretty sure this is not penetrating damp though I should say that there is an underground drain (for wastewater from the house) running somewhere along this wall that I have not yet had inspected and will do to be sure it's not contributing to this problem.

Also, I should note, there has not been any rain for the past few days and although there is pipework / guttering on this side of the house, it was all checked recently and cleaned / sealed up. There are no signs of water running down the wall.

Continuing on the assumption that this is purely a condensation issue, what would people recommend in terms of a solution? A vent in the outer wall, or in a stair riser above? And / or one in the (wooden) spandrel?

Also, is there anything besides ventilation we could try? To me, this looks like quite a bit of moisture and I just wonder if a couple of vents in this (unheated) space is going to be enough.

 

[Mr diy a lot.]

I’m not buying the condensation hypothesis. It’s just not adding up. The faint damp smell, the blown plaster and the sheer volume of moisture that seems to be collecting all in a property where you have a new dpc, new plaster to brick, the cavity wall has been upgraded - it’s is all good healthy property maintenance

I don’t see how it can be anything other than a slow leak/drip type issue that has probably been leaking for years. I would be getting on to that waste pipe you mentioned and rule that out before you do anything else.

Sounds like a pest but you’ll get to the bottom of it somehow and eventually with a bit of perseverance. Good luck.

 

[JohnD]

where is the water supply pipe?

have you got a water meter?

 

[tell80]

OP, Its not condensation.

1. Can you post pics of the outside wall - full elevation & at ground level?
2. Being on a hill, even a slight slope, puts you at risk of ground water pressure from up hill.
3. What type of DPC was installed in the outside skin? Why?
4. In the pic, where's the DPC on the inner skin?
5. Do you know the height relationship between the FFL & the outside ground level?
6. Who cleared the cavity? Who checked?
7. Who removed the CWI? Who checked?
8. Something odd about the solid floor in the pics - is it a screed or a slab?
9. The suspect drainage you mention can easily be tested for soundness.
10. What material was used to plaster the wall?
11. Have you probed the stair stringer for rot?

The important DPC is always the inner skin DPC.

 

[Nige F]

.Unusual place for condensation

 

[houseonahill]

Hi all, so since posting I have had the drain guys out to survey the drain - no cracks whatsoever and it doesn't even run right along the wall, it's probably about 1m away and well below ground.

I've also spoken to the damp specialist who diagnosed some of the other damp problems we had. (Before you start, he's an independent surveyor and wasn't selling me nonsense treatments! He correctly identified problems with moisture in the floor and cavities in other parts of the property.)

He says this is condensation because of where the damp patches are appearing and the fact that the water beads are clearly present. He also checked the location of the inner DPC, which he does not consider a problem here (it is about the same level as the floor) and advised me to keep the cupboard door open to let it dry out. 24 hours later, it's looking dry as a bone in there. He thinks that the cause of these patches is ultimately moisture in the air, quite likely largely from recently poured floor screed in the rest of the house.

We had to leave this area under the stairs unexcavated (no new damp proofed floor like the rest of the GF) because we couldn't afford to rebuild part of the staircase etc if we dug out the ground beneath it. So, yes, it's possible that some moisture is coming up through the floor here but the specialist says that he does not think this is a major issue and would be manageable with a breathable floor covering and some vents.

So basically that's what he's advised - I'm now considering whether to install vents in the cupboard door or in the stair risers. (High and low in either case, to improve air flow.) Any tips on that??

To answer some of your questions @tell80 the floor is some sort of concrete or screed, not tarmac. This side of the house is indeed that to which the hill slopes down from above so yes some water pressure from the side could be a problem. However, the builder put a new DPC in the outer leaf as a precaution, we could see the old bitumen one was still in place. And he provided pictures of the cleared cavities. The cavities were checked by the cavity wall insulation removers and myself as well. I know those cavities are clear! There was some rot at the base of the bottom step of the staircase, so it was replaced and a repair (including DPM) made to the patch of flooring below that bottom step before it was installed.