High humidity levels during rainy spells

[DaveG]

It is a very muggy and humid summer but is it normal to have 80 to 82% humidity in an older stone house at this time of the year? Circa 1870s build. It smells more musty during wet days but I’ve not had any mould issues as yet. We only moved in 2 months ago.
Given how warm it is we have plenty of windows left open and even the front door is left open for large parts of the day.
I had a VapourFlow humidity controlled extractor fan fitted a couple weeks ago in the kitchen and it’s just been flat out the past 3 days.
The house does undoubtedly have some issues with damp but in previous weeks we’ve had levels at nearer 65 - 70% RH. It’s seemed particularly bad the last couple days with the sustained rain.
Given the house is airing all the time, could it be that we’re actually bringing in damper air in and we’d actually be better off not leaving everything so open?

 

[LadyArowana]

Left to its own devices our half basement level would probably have those sort of levels. We run a dehumidifier 24 7 to keep it 60’s. In Summer we are pulling out a tank a day, less in Winter. If we are away it goes off and on returning it’ll be 80’s ish in there

 

[Lacan07]

It is a very muggy and humid summer but is it normal to have 80 to 82% humidity in an older stone house at this time of the year? Circa 1870s build. It smells more musty during wet days but I’ve not had any mould issues as yet. We only moved in 2 months ago.
Given how warm it is we have plenty of windows left open and even the front door is left open for large parts of the day.
I had a VapourFlow humidity controlled extractor fan fitted a couple weeks ago in the kitchen and it’s just been flat out the past 3 days.
The house does undoubtedly have some issues with damp but in previous weeks we’ve had levels at nearer 65 - 70% RH. It’s seemed particularly bad the last couple days with the sustained rain.
Given the house is airing all the time, could it be that we’re actually bringing in damper air in and we’d actually be better off not leaving everything so open?

I wouldn't get too disheartened, those humidity meters aren't very reliable. Mine shoots through the roof every time a black cloud approaches the house regardless of whether it rains or not. It won't tell you much about levels of moisture in the fabric of the house.

 

[CliffordPope]

Given the house is airing all the time, could it be that we’re actually bringing in damper air in and we’d actually be better off not leaving everything so open?

I've just read that the outside humidity when it's raining is about 90%. So surely ventilating the house when it's wet outside is just letting damp air in?
If it's hot air as well as damp then it will make a beeline for the walls and solid floors and condense because their temperature will be lower than outside.

 

[aockenden]

Yes we’ve been exactly the same this year. It’s been extremely humid outside and so with windows open we are rarely below 75% and during rain we’re into the 80’s as well.

Last year during those 6 weeks of drought at the start of summer I remember the RH is the house with windows open dropping to 40% at times.

So either we have to accept and get used to these higher relative humidities in order to get fresh air to breathe, or you shut everything up and run dehumidifiers to try to create a local pocket of drier, albeit stale air. So far, we are choosing the first option as it’s free (no electric cost for dehumidifiers) and we prefer fresh oxygenated air to dry air.

 

[DaveG]

Glad it’s not just me. I can’t quite get my head around why this was never the case in the newer property we had. I guess the air exchange was much slower with us not feeling the need to air things quite as much.
It does make sense that if you’re leaving doors and windows open everywhere that you’d get an equalisation of humidity with the outside which at times here is in the high 90s but that never seemed the case where we used to live. The only thing I can think of is if the building fabric is much dryer to begin with that it pulls some of that moisture from the air indoors?
I know our current stone built house is already holding moisture so my theory is perhaps it’s staying in the air more due to not having dryer fabrics to easily migrate to.
Winter will sure be interesting here. I hope we don’t encounter issues with mould. I’m installing what I can in the way of ventilation now to hopefully mitigate that over winter without the need to have windows open and freeze everyone!

 

[CliffordPope]

I've often wondered about the accuracy of these humidity meters. The one on our landing normally reads 80 something, and only ever goes down to 60 during a prolonged hot drought (rare in Wales). This reading is confirmed, very approximately, by other meters, but never agrees even approximately with what the dehumidifier says. But then it is only taking a reading at the dehumidifier itself, which is surely therefore bound to be wrong?

The strange thing is the house never actually feels damp, and paper remains crisp.
I wonder how they work? "Relative" humidity always feels like a false concept anyway - I don't want to know how damp it is compared with how damp it could be, I want to know how damp, in absolute terms, it actually is.

Our old rather twee little wooden house has Mr Wet and Mrs Dry who pop in an out twisting on a strand of cat gut, and they move exactly in accord with how things actually feel. I'm guessing they don't understand anything about Relative Humidity, and just show how wet it is. It is much the most useful of all these devices.

 

[LadyArowana]

Glad it’s not just me. I can’t quite get my head around why this was never the case in the newer property we had. I guess the air exchange was much slower with us not feeling the need to air things quite as much.
It does make sense that if you’re leaving doors and windows open everywhere that you’d get an equalisation of humidity with the outside which at times here is in the high 90s but that never seemed the case where we used to live. The only thing I can think of is if the building fabric is much dryer to begin with that it pulls some of that moisture from the air indoors?
I know our current stone built house is already holding moisture so my theory is perhaps it’s staying in the air more due to not having dryer fabrics to easily migrate to.
Winter will sure be interesting here. I hope we don’t encounter issues with mould. I’m installing what I can in the way of ventilation now to hopefully mitigate that over winter without the need to have windows open and freeze everyone!

Our newer property had a heat recovery system [ aka the magic snail ] and never needed ventilation. The one with half basement is Georgian and because of bugs and human miscreants the windows remain closed. There are things which people put into lofts to help ventilation, we don’t have that and for reasons it wouldn’t have been suitable, I expect someone else will chime in with more information, iirc they’re PIV systems [ not magic snails or some other name I made up ].

 

[Stonehouse]

It is a very muggy and humid summer but is it normal to have 80 to 82% humidity in an older stone house at this time of the year? Circa 1870s build. It smells more musty during wet days but I’ve not had any mould issues as yet. We only moved in 2 months ago.
Given how warm it is we have plenty of windows left open and even the front door is left open for large parts of the day.
I had a VapourFlow humidity controlled extractor fan fitted a couple weeks ago in the kitchen and it’s just been flat out the past 3 days.
The house does undoubtedly have some issues with damp but in previous weeks we’ve had levels at nearer 65 - 70% RH. It’s seemed particularly bad the last couple days with the sustained rain.
Given the house is airing all the time, could it be that we’re actually bringing in damper air in and we’d actually be better off not leaving everything so open?

Hi Dave

We’re 1850’s and I’m really struggling with humidity too. We’ve been decorating. Painting and skirting boards fixed a few months ago, but seem to be struggling with mould in a few areas on and at the bottom of the skirting. My hygrometers read high 70s to 80 per cent in those areas.

Like you, I keep opening windows, front door and now running a dehumidifier to try get on top of the mould. Maybe the walls are condensing or walls are still damp in those areas where skirting is as no piping where we have issues and no rising damp.

Any tips would be hugely appreciated.

I am nervous for winter!

 

[Jacky123]

I have a 17th century cottage and high humidity in summer. I run a very small dehumidifier downstairs all the time and the room is then comfortable. I have trickle vents on all the windows. I keep my clothes in the spare room on a rail, they always feel ever so slightly damp. I have read countless articles on this subject and it does appear to be a problem with older properties.

 

[DaveG]

I’ve conceded defeat for this year and started running 2 dehumidifiers on the ground floor only.
Obviously it’s made a huge difference but it’s a sticky plaster solution.
I’ve gone around the whole house these last couple days listing all the areas I know are contributing to water ingress and poor ventilation. It’s realistically going to take me 2 - 3 years to address them all but I’m determined to get this house dry and I’m confident it can be done.
I’m looking to buy a digital thermometer with infrared screen soon. They are expensive kit but there are some good models on eBay for under £200.
This will help me continue my learning of the intimate details of the house, including the damp areas around skirting boards even in internal walls which a few mention here.
I’m fairly confident that in 95% of cases this is internally generated moisture finding colder surfaces to condense and the IR thermometer will help me to visualise and prove this.
In my case a lot of my remedial works need to centre on improving airflow throughout the ground floor (I have 2 chimneys, both capped) and reducing rain ingress around the foundations from high external ground levels

 

[Lacan07]

I’ve conceded defeat for this year and started running 2 dehumidifiers on the ground floor only.
Obviously it’s made a huge difference but it’s a sticky plaster solution.
I’ve gone around the whole house these last couple days listing all the areas I know are contributing to water ingress and poor ventilation. It’s realistically going to take me 2 - 3 years to address them all but I’m determined to get this house dry and I’m confident it can be done.
I’m looking to buy a digital thermometer with infrared screen soon. They are expensive kit but there are some good models on eBay for under £200.
This will help me continue my learning of the intimate details of the house, including the damp areas around skirting boards even in internal walls which a few mention here.
I’m fairly confident that in 95% of cases this is internally generated moisture finding colder surfaces to condense and the IR thermometer will help me to visualise and prove this.
In my case a lot of my remedial works need to centre on improving airflow throughout the ground floor (I have 2 chimneys, both capped) and reducing rain ingress around the foundations from high external ground levels

yes, if you believe it to be largely internally generated then ventilation is the answer.

 

[CliffordPope]

yes, if you believe it to be largely internally generated then ventilation is the answer.

I wonder whether that advice still holds true in wet weather? I've measured the humidity outside on a few occasions and it can easily reach 90 when it's damp outside. Does inviting that moisture into the house really dry it?

The problem is it's seasonal. In autumn (and some summers!) it's sopping wet outside. In summer it can be hot and dry, but the house walls will be colder (average over the year) so attract condensation because warm air can hold more moisture.

The only thing I can logically see working is powerful extractor fans in bathrooms and kitchen to get rid of the moist air at source and stop it drifting into the house.

 

[chrisfraser05]

Do you have a nice dry loft space? If so have you considered a PIV unit?

I had one in my last place and plan on using one in the next place. As long as your roof/chimneys are kept in a decent state in theory pulling air from there into the house should force out your cooking/breath laden air though the nooks and crannies, vents etc.

One thing I started off doing wrong in my old place was opening a window during a shower, then it was cold as the extractor started just pulling air from the window and sending it out, bringing cold outside air over you as you showered, therefore you cranked the hot water higher to compensate.
Once I had the PIV unit and had a 10mm gap under the bathroom door, with the window closed and the fan on it pulled air from the house and out.

I have been going over ideas and I'm planning 2 PIV's, one feeding the upstairs landing and one feeding down through a cupboard and into the downstairs hallway by the kitchen doorway to help replace what the extractor takes out.
I'm looking at 400w heated unit. Granted the extra cost to heat the air will be noticeable on the electric bill, but the extra cost of rectifying damp and heating moisture laden walls with the central heating unit would also build up over time.

 

[chrisfraser05]

I wonder whether that advice still holds true in wet weather? I've measured the humidity outside on a few occasions and it can easily reach 90 when it's damp outside. Does inviting that moisture into the house really dry it?

The problem is it's seasonal. In autumn (and some summers!) it's sopping wet outside. In summer it can be hot and dry, but the house walls will be colder (average over the year) so attract condensation because warm air can hold more moisture.

The only thing I can logically see working is powerful extractor fans in bathrooms and kitchen to get rid of the moist air at source and stop it drifting into the house.

Regardless with the extractor you will be pushing air out, so the house will pull in air from outside. So in effect you have no choice that the outside air is coming in, but the internal air is going to be higher with the added humidity from human activity.
This is where it's best to choose where the air comes from (ie a PIV or a window/trickle vent) or have dehumidifiers or the like to deal with it when it does get too much at specific spots.

Even in autumn/winter, when the rain stops the air can dry out pretty quick. This is where the "breathable" materials of the house come into play. When the air is more moist than the walls, they should be able to absorb the excess, and vice versa when the air has less they excrete it back into the air, the objective being keep enough airflow going that over time the levels in the walls don't get excessive. Think of them as a moisture battery. Hence covering them with modern materials causes the barrier, they no longer act in that manner, and materials behind them that do allow the moisture in will have no way to release etc.

 

[CliffordPope]

Regardless with the extractor you will be pushing air out, so the house will pull in air from outside. So in effect you have no choice that the outside air is coming in, but the internal air is going to be higher with the added humidity from human activity.

But the house doesn't have to pull in any air. If you keep the kitchen or bathroom doors shut, and leave the extractor on for half an hour after use, the air can enter through an open window in the kitchen or bathroom and doesn't need to mix with the house air at all.

 

[DaveG]

I think the point Chris is making is if outside air humidity is high you are bringing it in regardless of which method you use. Any air exhausted has to be replaced. If it’s pulled in from another area of the house then the air in that area will be replaced. Regardless you will and should encourage outside air into the property. A healthy home should have multiple changes of air throughout the day.
The problem is if the house is damp to begin with, bringing in moist humid air from outside isn’t going to help dry it out whereas during the winter when the air is drier (but also colder) you will be bringing in less moisture from outside.
As Chris says, either way outside air is better than inside air but don’t expect much of a drying out process to occur over warmer months where typically in the UK that means humidity not dry arid conditions.
Only thing that puts me off about PIR is generally an attic space will have more contaminants. Dust can to a certain extent be filtered out but a lot of the finer chemicals associated with many modern insulations will not be and this is being introduced into the home.
I’ve heard good things about their effectiveness but if possible I think better to just go that one step further and pull in the air from outside the home rather than from within the loft space
Of course if you live on a busy main road that’s another issue there

 

[Cubist]

Personally I'm an advocate of more ventilation rather than less and have worked to ensure the free flow of air into and throughout the house. On balance I feel, particularly as ours is an oak timber frame, that this helps to minimise damp and therefore reduces the risk of pest infestation and other deterioration to the timbers. Whilst beneficial to the fabric of the property this is sometimes met with vociferous grumbles from some. However, while I could never be described as a fresh air freak, I will adamantly pursue this policy because.... I never, ever, again want to be trapped in a house with a flatulent West Highland White!

 

[DaveG]

Theres an opportunity for a magnificent typo there. White/Wife

 

[Cubist]

Theres an opportunity for a magnificent typo there. White/Wife

Ensuring I was not damned by either my own lackadaisical digits AND by the dreaded AutoCorrect was very much in mind. I survived the pooch - just - but a stratospheric First Lady not so much.