Damp under stairs cupboard – easy fix?

Old house has no dpm/damp course
Wall is mid terrace between to houses

The floor below the stairs is basically just dirt right down at the end under the first step

There was signs of damp above the stairs when I moved in which I hacked off and had replastered, with no actual fix for the damp (bare with me I was new to this)

The under-stairs entrance door has been off all year, and so has the adjacent kitchen door one so loads of lovely airflow, last week I put doors back on both the kitchen and under-stairs – et voila, big patch half meter square of damp 7 days later showing above the stairs

Thing is I want to keep the door on the under-stairs as it makes up the wall on one side of the living room and looks terrible with just the open space their

– could I keep it on (open up and vent the space above the door) door width and about 300mm high, then introduce louvre type vents on the vertical parts of the stairs to get air in from that side too? Maybe do the bottom 5 stairs on left and right?

In other parts of the house I’d stayed clear of injectable dpm type things but might be needed in this one spot to help

In future I’d also keep all doors open when away from the house / work etc

What’s the airflow like under the floor? Can you put a vent in to use this to ventilate the cupboard area. Alternatively, louvre door?

Its a thin slab with soil underneath in the living room, the same under the stairs but the slab is pretty much none existent the tighter under the stairs you go

Louvre door could be a shout, annoying as I’d just picked up 3 1930s 3 panel doors for the living room s/h, the worst one I’d trimmed down to make fit and put it on the under-stairs, that might get some vents put in the base board yet

Don’t inject anything into the wall. It is nothing but snake oil. Buy a copy of Peter wards book warm dry house.

Agree ajc, I’ve watched a lot if his YouTube videos, my place is a classic example if built old methods modernized new (not by me) so I’m doing my best not to make things worse

What you need is proper airflow if the base is partially just dirt. How about a louvre vent into the lowest riser of the staircase and a vent in the base of the cupboard door?

Not going to be easy keeping anything in it, it will obstruct airflow and just get mouldy, I’m guessing.

Yeah this is what I’m thinking, but possibly adding vents to the first 4 maybe 5 risers, I was going to put a carpet runner over the top but I’ll chuck them in and just paint the whole stairs for now, then experiment with putting a peice of carpet over them in future once things have calmed down a bit

Luckily the back of the cupboard is mostly old wheels and racks so there’s room enough for air flow and no big shelves or anything sat up against the walls

As above, ventilation will help massively, but can you check with next door to see if they have had an injection DPC along their side of the wall?
If they have, moisture could potentially rise up then bridge across to you.
I had exactly the same problem in one of my houses (the whole row of terraced houses floods under the floors in heavy rain) and to be fair I had to do a mortar layer DPC, re plaster and vent the cupboard. Been fine since.

Good timing this.
Have noticed ‘rising damp’? No not Rigsby lol on one of our party walls in a cupboard in the dining room.
I was thinking/dreading that we’d have to get dpc injection done at some point, not realised that it’s ‘snake oil’…

That, surely, is a euphanism…

@granny_ring damp in a cupboard is condensation forming on a cold spot with lack of ventilation. Normally on external walls but party walls can be thermal bridges. Is it on the side of a chimney?

Our understairs cupboard gets a but damp in wintertime, so we chuck a dehumidifier in there. Works a treat.

@granny_ring damp in a cupboard is condensation forming on a cold spot with lack of ventilation. Normally on external walls but party walls can be thermal bridges. Is it on the side of a chimney?

Yes it is, Cupboard built in the recess. Have also got damp on the front face either side of the blocked off opening.
There is a vent just above skirting height.
Tbh, the cupboard was full of junk so once it’s dried out things will be stored in those plastic storage boxes leaving room for air to circulate.

Could you source a timy 4in cpu fan from RS components. Place this in the stair riser. Then fit a low level mesh vent in the door. The fan will draw slightly warm air into the area and up and out again
Moving air dries things better than stationary air. Cost pennies to run, almost silent, slim and cheap. A silent bathroom extractor on a humidistat would work but cost 4x the amount, are bigger and the humidistat can fail

Thanks guys, CPU fan is interesting, sit next to a bunch of electrical engineers at work, my first question, how to power it!

Does it matter particularly where the vent is as long as the space is ventilated? Or should they be low to the ground close to the issue? I guess the latter, just looks better on the door side to vent above the door where there’s already a gap, than fit a vent into the door base