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.

Afraid I have no advice but following as my house is similar. My lounge is north facing and we live in a rainy part of the country - my sofas smell a little musty sometimes but no other signs of damp anywhere. Still drives me mad though!

Keep the windows and internal doors closed during a cold night. Look at all the windows early in the morning to see if any room was particularly damp. That may indicate a source of water.

There might be a roof leak problem, get a good torch and look in the loft.

Walk round during and after rain looking for signs of spilling gutters or downpipes, and around windows inside and out. Bays are particularly troublesome in older houses.

How do you ventilate the kitchen and bathroom?

Do you dry laundry indoors?

UK houses usually have lower humidity in winter than in summer due to central heating. Round about 50% humidity is normal in my house.

We have water rising through the gaps in our brick floor ( old house ) as it sits over a well. I know that because there’s an old hand pump too

Weirdly apart from the wet floor it never causes any mould etc and just dries out when it doesn’t rain.

Ventilation is key

Yes I ventilate like crazy, better than the Germans with their "luften" !

Your house sounds amazing with your well and hand pump. Water rising is a pain though.

I wonder if I've no mould or damp patches because between very wet periods the place can dry out completely. And the luften of course!

I have temperature and relative humidity gadgets in every room so I know 2 rooms are the worst and these are the ones where the ground outside is saturated after rain. Small enough area, 2-3 metres square and the rest of the garden will dry out completely while these will stay wet for ages which makes me think the water is coming up from below..

Laundry is line dried and finished off in bathroom if necessary.

Bathroom has a useless extractor fan so window is opened after showers until all the shower moisture is gone. Can be chilly but has to be done.
Kitchen has an extractor fan for when cooking, will crack open the window too to aid ventilation. I really do everything to keep the relative humidity down.

What temperature is your house when you get readings of 50% RH?

Ventilation is key- I’m having vents put in bathroom kitchen, additional trick vents too

Yes trickle vents open here all the time unless there's a gale blowing in.

It's damp and misty here this morning but I opened the kitchen window for 10 minutes and RH went down by 3%

We had a leaking pipe under the floor that caused similar problems to yours. The rain tipped it from the water from the leak draining away to some pooling. All the self defined experts (neighbours, family members, post man, friends) said it was a rising spring despite the geomorphology making it a physics defying possibility.

We turned the water off at the stop tap and the meter on the stand pipe was still ticking over. Which indicated that there was a leak somewhere between the street and the house. It turns out that it was an old stop tap under the kitchen units buried in rubble from when a previous owner had an extension done.

If the water meter in the street doesn't go around turn the stop tap back on and turn off all your taps and check your meter. If it is going around then you have a leak on the house side of the stop tap.

If the water meter doesn't go around in either case it isn't a leak and you have an issue with ground water. Digging a ditch on the down hill side of your house and backfilling with gravel or a perforated pipe can reduce the water level in your house.

It took us over 2 years to find the leak in our house... Ironically when we gave up searching for the leak and put a new supply in.

Get a dehumidifier. Run it a lot.

I’ve just bought a humidifier. The front of our house is around 65%.

Chat GPT said it can be caused by the front of our house being old (and rendered) and the back of our house being new and insulated.

"I have temperature and relative humidity gadgets in every room so I know 2 rooms are the worst and these are the ones where the ground outside is saturated after rain."

How old is your house?

Is there a gulley or downpipe outside these rooms or nearby?

Are you on a slope?

Are the floors concrete, or wooden? If wood there should be some airbricks in the wall above ground level. Can you see them? Sometimes ground level is raised too high by paving or flowerbeds. Photos would help.

BTW I agree with the waterpipe hypothesis for water coming up through a floor.

OP if you’re up for a bit of digging you could create a soakaway. Starting at the 2/3m2 wet area in your garden dig a trench running away from the house. Fill with rocks/gravel then cover back over with soil and your grass.
The wet won’t pool near the house then

"Bathroom has a useless extractor fan"

I can probably recommend a better one. Does yours fit a 100mm duct through the wall, and does it have a timer run-on?

Do you have steamy showers?

Concrete which doesn't help as they are so cold.

Yes it has a timer but once or twice I've tried leaving it run for over an hour and the RH hardly changes. If I put a thin piece of tissue up to it it can barely hold on to it. I just open the window as it's so pointless.

Let me check about the duct size....

Relative humidity here, outside, is 97%. It won't be much lower inside, I suspect, as it's been sunny so all the windows have been open.

18 isn't that warm. Try bumping the temp up a degree or two and run a dehumidifier. Our living room can easily hit 70% in the winter and the rh outside will often be higher as it's just a damp part of the year

I'm not convinced that there's a problem. It's really mild at the moment so rain will evaporate into the air more. My weather app tells me that the outdoor RH is averaging 83% and it's not even rained for a day or two. I generally find that at the beginning of winter the indoor humidity is high and drops as it gets colder. Currently it's sitting at about 75% without a dehumidifier running, which looking back at my heating app is the same as September last year when outdoor temperatures were similar to now.

As it got colder last winter and we were running the heating more the humidity in the house dropped to as low as 35-40% (even without a dehumidifier).

We don't have any mould or condensation so I'm confident that we don't have a leak or anything, it's just weirdly warm with high humidity for the time of year.

Depending on the age and construction of the house, they will be more or less damp.

How old is it?

Can you see the DPC outsde? It will be a thin black horizontal line in a mortar bed usually 6 or 9 inches above where ground level used to be when the house was built.

Even with windows open the RH should be lower indoors due to the higher temperature. My problem is that the RH can be higher indoors than out even on a damp misty day with 99%outdoors. I can open the windows on a day like that and the indoor RH will drop.

House is approximately 45 years old. No sign of a damp proof course. The fact that the 2 worst rooms are right next to the wettest parts of the garden makes me sure that moisture is coming in somehow. It's just that the lack of mould or damp marks on the walls has the housing people saying there is no damp problem.

We had problems painting the place too. Bubbles popped up on the ceiling and a painter said it could be because of moisture in the ceiling. Also problems painting the walls and this was al following prolonged rain. Painted after a long dry period and no problems.

Oh crikey. That sounds an entirely different kettle of fish. Hope you get a resolution.

• No RH isn’t always lower indoors than out

warm air holds more moisture and mixing humid air and warm air creates moisture which holds in the air for longer

Temperature difference: If your home is air-conditioned or just cooler than the outside, the indoor air is holding a given amount of moisture at a higher relative humidity.
Indoor activities : Everyday actions release moisture into the air, including cooking, showering, washing/ drying clothes, and even just breathing.
Poor ventilation : If there isn't enough air exchange between the indoor and outdoor environment, moisture can build up inside.
New builds: Newly constructed homes can release stored moisture from materials like concrete, leading to high humidity for a period after construction.

The best solution is to improve ventilation or / and use a dehumidifier if it’s becoming a problem.

"House is approximately 45 years old. No sign of a damp proof course."

I presume you are in UK? Damp courses gave been compulsory much longer than that. Either you can't see yours, or it has been buried by adding paving or raising the ground level against the house. Which would cause damp.

You might be able to see it on some other wall. It is often visible beside or below a doorstep, or in an unplastered room or inside a cupboard.

"House is approximately 45 years old. No sign of a damp proof course."

I presume you are in UK? Damp courses gave been compulsory much longer than that*. Either you can't see yours, or it has been buried by adding paving or raising the ground level against the house. Which would cause damp.

You might be able to see it on some other wall. It is often visible beside or below a doorstep, or in an unplastered room or inside a cupboard.

Can you post some photos of an external wall showing the ground, and the first few courses of bricks? The wet area would be ideal.

*!875 in what was then London, shortly after, in other major cities, varying dates elsewhere.