Damp house but no sign of damage, just high RH after a lot of rain.

[Greysowhat]

I'm in social housing and the place is fine unless it rains for prolonged periods. When it does the relative humidity (RH) goes up and up. When the weather changes to dry conditions slowly over days the RH comes down again.

The locality has damp ground and I think we are quite close to the water table which rises when it rains. Springs pop up in the local park after an awful lot of rain over days and days! The garden has 2 very wet areas which are close to the 2 worst rooms. I wonder if a spring popped up under the house or maybe it's just sitting in water when the water table rises.

I've been on to the housing people many times about this but unfortunately there are no actual signs of damp in the house such as a smell of damp, mould, crumbling skirting boards or damp patches on the walls. So they say there is no problem. But a couple of weeks ago after a lot of rain the RH was 80%, with temp 18 degrees C.

I ventilate like mad when the house is damp so that would keep mould away.

So can anyone tell me how the place can feel so damp and yet no damp patches or other damage anywhere.

Basic method short of taking the roof off
Go Into the roof in the day. Don’t put any lights on and see if the outside light shines through. If it does that’s the problem area

Other methods are going around with a damp meter and finding the location of highest readings. Then opening up ( from the outside ) to see what the issue is.

Unless your roof has exposed dpm ( some flat ones do ) these are the only ways to check without removing the whole roof - which you should never do without further investigation ie damp meter

If it’s a flat felted roof someone can take a look just by looking at it

Where I am, crawl spaces normally have standing water because the water table is so high. It doesn't mean that the house is damp, just that there is water under it. You do have to make sure it's well ventilated and heated though, otherwise it can get damp.

Yes, but this house has a concrete floor.

I just realised how old this thread is and that you'd been really helpful! My house actually has a concrete floor, but the floor is suspended. Concrete raft floor is a different kettle of fish

Thanks everyone, especially @PigletJohn and @DrPrunesqualer for all your input.

Just to mention that over a year ago they installed a PIV in the attic as I was complaining of the high RH. Well it didn't make much difference I think because my vigilant ventilation was doing the job already. And it was pumping in horrible musty air from the attic so I turned it off. Would musty air from the attic indicate a problem with the DPM up there?

Also a couple of the interior doors stick after prolonged rain. So another thing that says a damp structure to me.

The housing people had another look recently and said the house was too cold. The walls were cold they said. They advised turning up the thermostat to 20 C and leaving the heating on all day in every room and leave it on even when going out. This it to maintain heat in the house which will help with the problem they said. I'm doubtful! But I agreed to try it anyway although seems like my next gas bill will be massive. I've to come back to them in a month if it hasn't helped. I know it won't other than reducing the RH purely because the temp it higher. The worst it has been is 18.3 C and 82% RH following a week of more or less constant rain a few weeks ago. Turning up the heat to 20 that day would still have left me in a sultry 73.8% RH !

So when I do go back to them can I say that staining on the back wall is a sign of damp? What should I ask them to investigate further....

The DPM in the roof space and at the foundation?
The down pipes in the back? The one in the front?

Anything else?

Thanks again 😊

Spaces that are not used do over time smell musty
However
Roofs also need ventilating. This is part of the construction and at the eaves and Sometimes at ridge level too

If it’s musty up there I’d check for RH/ damp. It could be that over time the roof is no longer ventilated.
This can so easily happen….a loose ridge tile gets cemented in without any realisation that tile was supporting ventilation. …. a rotten roof soffit gets replaced without anyone noticing the old one had vents.

So check the roof space just as you have been doing with the rest of the house

You shouldn’t have to keep the temp at 20c. They are trying to get you to pay for a problem they need to sort

Its obvious if you raise the temp things like your doors will dry out and stop sticking ( wood contracts when it’s hot ) but as soon as that heat is turned off you’ll be back to square one.

I’m beginning to think your ha guys know nothing about how buildings work at all.

Ask them to do a survey by an independent building surveyor. It’s worth a try

You shouldn’t have to keep the temp at 20c. They are trying to get you to pay for a problem they need to sort

Yes I agree. The maintenance guy was here and his boss who was supposed to be more of an expert. Turned out he was a plumber who'd done a course, on what I don't know but he said he'd done one! I knew more than he did. I don't think he even understood relative humidity. I had to keep saying it was humidity relative to temperature and he just looked at me blankly. They kept focussing on the house being cold. The plumber even suggested we keep the heating on all night! Ha!

So I'll do this experiment for them or at least on paper. I'll convert the RH readings as if the house is 20 degrees and do a nice Excel document with graphs and everything! We're used to 16.5 - 17 C in the day time, moving around it's fine. 18 - 19 C in the evenings, we dress for it and it's fine unless very damp and then it's uncomfortable. But damp is uncomfortable at any temp.

Thanks so much again!

Just dragging up this old thread to update.

I bought one of those moisture meters and checked around the house. The walls all seem to be ok which surprised me as I was sure it was rising damp. However I discovered a lot of damp patches on ceilings. The rooms with the worst RH problems after rain have the worse damp patches. Following 2 days of rain and coincidentally not using the shower, the bathroom ceiling has around 500 mm of the meter in the red and it progresses across almost all of the ceiling dropping by a few percentage points the further I go from the wall.

Also found damp at the back door by the saddle. The saddle is in the red zone and I an get the prongs into the concrete beside the saddle and that's in the red too. Can't get at the concrete any further into the room.

So looks like the roof might be a problem?? Or what else??

The back door has been moved during a renovation to remove a back hall before I lived here and it seems to be positioned right where the DPM is, or where we think it is under that pebbledash line so I'm guessing it is compromised or removed during the renovation. How big a fix would this be?

Just to add, the damp areas on the ceiling are not associated with any downpipes.

What’s the ‘saddle’ ?

Yes
When the moved the door they have bridged the gap and need to redo that area.

The threshold I suppose, although it's just a strip on this side of the door, not actually underneath the door.

OK, thanks.

We call the door surround the jamb or architrave if it’s the cover piece
If the door is well set into the wall and the wall makes up the enclosure without framing then it’s the reveal.