Does my home have a humidity problem?

We’ve lived in our home for over 25 years and I’ve never considered it to have an issue with humidity.

A year or so ago I added some Aqara temperature and humidity sensors to my HomeAssistant system, but haven’t really paid much attention to the humidity readings until now. I’ve noticed this week that almost every room has humidity in the 70-80% range. It obviously varies over time and with temperature but most of the sensors are reporting consistently well above 70%.

We’ve never had any issues with damp or mould, but from what I’ve read 30-60% humidity is considered healthy.

We’ve not put the central heating on yet, so the temperature is between 15-17degrees in most of the rooms, but I’m not sure how that affects the humidity.

Should I be concerned about the humidity in the 70-80% range?

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The normal measure of humidity is as a % of saturated vapour pressure. In effect it is a measure of how much water vapour the air can hold at a given temperature. Without changing the amount of water in the air the humidity will go down if the room warms and up if it cools.

At 70% humidity in the middle of a room there probably won’t be problems although bacteria and fungi will survive better than at a lower humidity.

If that same room has cold walls then as the humid air touches them the local humidity will rise, potentially above the dew point, and water could form as condensation.

My understanding is that the ideal range is 40-60%. Below 40 the air becomes drier. For a while this won’t matter but you will get more drying from your eyes and lungs and therefore need to keep yourself hydrated by drinking more. Below 30% or so viruses thrive better, hence the advice you may have seen about humidifying dry rooms during the Covid outbreaks.

High humidity in a house is often generated in the house, for example kitchens and bathrooms and carried into other rooms by air movements. It could also be a result of poor weatherproofing if it appears to be related to wet weather.

To prevent internal humidity from building up you need to have extract ventilation in any room with a source of dampness. Opening windows won’t be adequate if the wind has dropped or is blowing into the window and carrying the humidity further into the house.

Hi, I manually logged temperature & humidity readings during renovation and still do monitoring now. The readings you reported are high and you are likely to see a progressive appearance of mould on surfaces such as wallpaper and the tops of skirting boards where dust collects. My monitoring picked up a leak in our roof when humidity shifted from 50-60% to 70-80%. ~I use cheap monitors and calibrated them by leaving the units together on a tray in kitchen and monitored readings to check variance and spread in recorded values.

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For 25 years we lived in a stone solid-walled house with no dpc. The humidity was 78-80% for most of the year. Although for the last 5 years we had MVHR it was too late - our books had gone moldy. We now live in a 1960s house with EWI and MVHR. The humidity is normally between 40-60%. A bit too close to 40% in the winter.

Does this look familiar @Peter_Livesey ?

My sensors are a mixture of Aqaua and Sonoff. As you can see, much of my house has humidity readings of 60% and above all year round. It’s much worse during the summer months when the heating isn’t on. Due to warm autumn, the heating still isn’t coming on enough to keep the dampness at bay (heating to 16 overnight, 17 during day and 18 evenings). On sunny days I make sure to open windows on both ground and first floors for an hour or so, but I don’t tend to do that during wet and windy periods, and I don’t think it helps when it’s damp outside anyway. My daughter visited last week and said downstairs smelled really damp. Waiting for some damp proofing and a MEV ventilation system to be installed, but while I wait books, papers, shoes and textiles all deteriorating :frowning_face:
I’m really concerned about high humidity!

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Hello. I have a condensation problem behind the bed head against the north wall of the house.
The wall is cool and colder in areas where there is less air circulation. Air can hold less water as it cools, the water begins to condense out of the air when the temperature drops to the dew point.
A psychrometric chart shows the behaviour of water vapour in air. If the relative humidity at 20 degrees is 40% the dew point is around 7 degrees, something would have very cold for condensation (single glazed window).
In a more humid house with relative humidity at 20 degrees of 70% the dew point is around 14 degrees so it is possible to to have a cold spot subject to condensation.
Please note my reading of the chart on screen is not very accurate and there are probably more mechanisms effecting condensation.
I think the solution to a condensation problem will be a mixture of insulation and ventilation and I am going to investigate further…
Does anyone know more or have any comments.

The reduced airflow behind the bed will worsen the damp/mould. Can you blow a fan on the damp area or rearrange the furniture so that the air flows freely across the outside wall?

In a previous house with a damp cellar, I fitted a stainless steel Wind-powered chimney fan Cowl. This did reduce humidity significantly in a short period of time. This is definitely worth doing where chimneys are not in used and if there is subfloor access. This can assist other methods e.g. drains etc and relatively quick to do.

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@lloydham ’s solution may be relatively cheap to install but the apparent free running costs actually cost you all the heat in the air being extracted. That isn’t so good in an occupied room.

MVHR is the way to go. Controlled extraction whether it’s blowing a gale or totally wind still and you get your heat back.

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Just thought I would share a recent experience- We generally do not have an issue with damp or humidity but we were away for five days and left the windows covered and came back to a bit of mould growth on the window. By the growth pattern around the edge of the frame it looks like the seal might not be tight enough?

Obviously I wont be leaving windows covered for an extended period.

That effect can be achieved without any air leakage. If there is limited air circulation and the frames are being chilled then the relative humidity will rise. The frames on most windows have a ridiculously high U value.

Just before Christmas we spent 6 days in north Wales. Our home heating was turned down to 10 °C to avoid freezing (there was snow and ice outside). We also left the MVHR running. Our MVHR has an automatic flow control, so as moisture generating activity drops, so too does airflow. If we didn’t have that function I would have reduced flow manually, but we had left a full load of washing to dry while we were away (yes, at 10 °C). Some curtains were left closed.

On our return there was no sign of damp in the house, or the clothes.