Humidity help

Two years ago we moved into a detached 1950s bungalow, after we moved in it felt like it rained for months on end the constant rain and it being winter resulted in a huge humidity problem resulting in wet ceilings with black mould growth in the rear bedrooms and lots of condensation on bedroom windows.

Initially I thought this was down to poor ventilation regarding the gas back boiler so this was replaced for a room sealed boiler, this made no difference.
After speaking to a builder I then fitted a Vent Axia PIV which gently pressurises the house, this eradicated the problem but basically meant the house was perpetually cold and given the cost of gas it’s not a long term solution.

Our windows are always left on the slightly ajar position so natural draught is higher than a trickle vent would be, the loft has approx 300mm of insulation, cavities are insulated. Both bathrooms have powerful extractors that over run.

I have just fitted an Evohome to individually control room temperatures to see if this improves humidity, it has but only by a 2/3%.

So in short our humidity rarely gets below 65% and often hovers at 70-72%

For comparison if I put the hygrometer a few feet away from the log burner it will drop to 45-50% humidity.

Am I missing something glaringly obvious to try?

Dehumidifier? It’ll reduce the humidity and warm the room at the same time, although there’s obviously an electricity cost to consider.

Just get one that has a hose that can go somewhere convenient, emptying the portable versions is tedious.

Just a thought but are you absolutely sure you don’t have a water leak somewhere?

Solid concrete floor or suspended? My money would be on a plumbing leak which has saturated the concrete floor, or made a lake under the floor if it’s suspended. Less likely cause is a defective damp proof membrane under the floor.

Humidity is a relative measure. It drops by the fire because the capacity of warm air to carry water increases so the relative humidity decreases. The actual water content will be more or less the same.

I have a PIV in the loft, barely notice it and certainly doesn’t make the house cold. You don’t need the windows open for the PIV to work.

felt like it rained for months on end the constant rain and it being winter resulted in a huge humidity

If the rain isn’t coming into the building I can’t see why it would result in so much humidity. Generally speaking constant rain doesn’t result in this sort of problem unless the building isn’t watertight or there is damp course issues, assuming that it was constructed correctly and that this hasn’t been an issue for the last 70 years.

I’m assuming that condensation on the windows is due to a lack of double glazing.

I can’t understand the wet ceilings if there isn’t a leak or damaged roof.

Edit : I would have a good ferret around next time there is heavy rain to see what might be occurring. Check in the loft and also for blocked rainwater pipes/gutters etc. You might be surprised to find water cascading in places where you hadn’t seen it before. Or a constant dripping in the loft.

It’s a much better idea to open the windows wide for a short time then seal them again. It clears out the moist air fast but doesn’t cool down the fabric of the building. So when you shut the windows the air heats up with the walls giving off heat.

Trickle vents are daft, you need to replace the moist air regularly imagine how much air an unforced trick vent lets out.

Although i’m dealing with older ie pre 1900 property at work they are more often than not also experiencing damp issues. As always try and eliminate all possible sources of damp, starting from the top.

So check your chimney first
– does it have a rain cap or cowl?
– is the haunching in solid condition with no cracks
Then check the roof – any possible leaks/slipped slates/dodgy flashing? Get in the loft and look for signs of water ingress or daylight through the roof.
Then check all gutters and down pipes are clear of debris, don’t overflow or leak.
Then check the render if you have it – any cracking
By now you’ll be at ground level – do you have wet soil/material up to the base of the walls.
Are you built on a slope – could water work it’s way toward the building downhill?

Once you’ve done all that, which won’t take long, and are satisfied, start thinking about potential damp generators inside. As others have mentioned, ventilation is very important, especially if drying clothes inside during winter months. In my own house we open doors and windows for 20 minutes to blow air through now and again.

Check in the loft and also for blocked rainwater pipes/gutters etc. You might be surprised to find water cascading in places where you hadn’t seen it before

Ernie is dead right, I have lost count of the number of customers who say their rain goods are all fine only to be on site in a rain shower and watch it all cascading over the gutters or out of a blocked downpipe!

You mention you have cavity wall insulation, that is not always appropriate in some buildings so that might be a cause for concern long term

A dehumidifier such as a Meaco Junior will make life much better so consider one of those. It might not fix the root of the problem though

The property has older double glazing, there aren’t any leaks as in the roof as I have been up to check that along with gutters and valleys.
It’s on suspended timber floors.
There was previously a leak on the chimney but that’s been repaired.

What would be an average reading for humidity in a building?

Having two dogs the back door is nearly always open/ajar.

Thank you for all your input 👍

I’d say our place is around 65ish in average  in the winter, higher in damp low presssure conditions, lower when high pressure takes over. Less again in the summer. Thermostat set to 18.5.PIV solved all our mould/condensation problems in weeks of fitting.

Remember most humidity sensors are probably only accurate to +-3%.

Property I worked on last year went from 85% or so humidity down to a very pleasant low fifties after removing cement render and allowing it to dry out. It was then re harled in lime. The cement render was cracked and allowed rain water in behind which then saturated the early victorian stonework. Being cement, the render then trapped the moisture within the fabric of the building which left only one place for it to go – inside

I could get to 55% if I ran my heating at 21deg. Prefer a cooler house though…

Prefer a cooler house though…

Yep!

Have you looked under the suspended floor?

Squirrel is right, even a tiny leak under the floor will saturate the solum if you have one. Years ago I had a plumber tell me he’d put a continuous run in under the floor and that it couldn’t leak. Turns out he’d put a joint in the middle of the run that leaked a drop every minute. Over a year that’s a lot of water. We stuck the dehumidifier down a hatch in the floor and ran it for a week

https://www.richard-stanton.com/humidity-calculator/

useful calculator here that’ll show you how air temp affects relative humidity.

This is what I don’t understand :

resulted in a huge humidity problem resulting in wet ceilings

I wouldn’t expect a ceiling with 300mm of insulation above it to be cold, so I can’t see how that is condensation.

Surely there must be a leak somewhere. Have you actually looked (and listened) in the roof space when it is raining heavily?

Where is your house OP? Exposed location?

We have 3 de humidifiers running a few times a day to get the levels under 60% and control mould (that loves over 60%).
I do live in a cob walled cottage (with thatched roof) though and think that just goes with the territory.

I’m not sure humidity itself is an issue. Jambo is spot on in terms of it being a relative measure.

Is the problem actually humidity or that you are getting condensation. There are two things to look at. Where the humidity is coming from and why it is condensing on surfaces.

One simple check would be to see if the humidity is the same inside and outside the house. Although that is harder in winter when you have the heating. This will tell you if you are generating the humidity through something that is happening or if it is natural.

Look for sources of things that generate humidity. People breathing, cooking, burning, drying clothes, damp etc. as others have suggested.

If the issues is condensation then it is because the surfaces are below the dew point. Basically warm, humid air contacts a cold surface, cools and the water condenses out onto that surface (like breathing on a mirror). In that case you need try and eliminate the cold surface. Insulation is the obvious solution. Next is trying to keep things warmer. Its fine having a cool house but not if it get’s cold while you are out or overnight. The other option is ventilation active, or passive but you need an air flow to prevent the humidity from building. Either pushing warm or dry air through.

In a well sealed house, that is relatively small for the number of people a dehumidifier may be the best option.

Sorry to join in on this with a thread hijack but looks like there’s a lot of knowledgeable people here and it got me thinking!

Are dehumidifiers preferred over using trickle vents in the windows?

Our previous flat didn’t have trickle vents and leaving the windows on the catch let in way too much cold air so we used a dehumidifier a lot, especially in winter. However got a bit of a shock when the electricity bill came through!

We’re now in a house with trickle vents which are constantly open and we don’t seem to have any issue with humidity or dampness however definitely conscious of the constant stream of cold air trickling in through the vents. It’s a relatively new house and having the stringently controlled wall and ceiling insulation seems a bit pointless with such constant drafts coming through…

The house gets noticeably stuffy if you close the trickle vents so I guess it comes down to the cost of running a dehumidifier for a couple hours a day vs the cost of the extra gas required to compensate for the trickle vents being open all the time?

Also saw automatic humidity controlled trickle vents online; any one any experience of these sort of things?
https://toma24.com/productcart/humidity-sensitive-trickle-vent-higroster

No amount of dehumidifiers are going to get rid of co2 or voc off gassing in your home. You shouldn’t be using one instead of having fresh air.

definitely conscious of the constant stream of cold air trickling in through the vents.

Either they are broken

Or your subconsciously aware you have left them open.

Because that’s not how trickle vents work. If you can feel it then they are not working as they should. It’s a tiny controlled volume rather than a draft you can feel.

This sounds a lot like my girlfriend’s old house, which had a damp problem in the loft, on account of there being no ventilation up there. We got a roofer to install some vent tiles and that fixed it.