Humidity in the house - how to control it?

LeoC

Hello

Not sure if this is the right forum, but I thought I'd ask.

Some time ago my doctor told me that I am severely allergic to dust mites and that I should try to keep the humidity in my home below 50%, so I started to check it with hygrometers and control it with a dehumidifier.

What I don't understand is what are the drivers of humidity, I thought that everywhere in London humidity should be the same, but...

I have lived in 3 different flats in London recently with very different levels of humidity.

Flat 1 was a top-floor flat in a converted 1860's house, London Zone 2, around a leafy/green area. Single glazing, single brick walls, very draughty, very badly insulated. Humidity there was 60% in the summer, 55% in the winter or so.

Flat 2 was central London zone 1, very urban, modern block, double glazing, cavity walls, built in the 1990s. Humidity there was very low, around 50% all year.

Flat 3 is Zone 3 London, in a 1950's block. Cavity walls, double glazing. But humidity here is even higher, 70%+ now in the summer. Lots of trees around, woods, and forests. Very green.

So I don't understand how in the same day humidity in one flat is 50% and another almost 80%? And all the flats are around 5 miles from each other.

I am looking for a place to buy, what are the main drivers of humidity? Is it location (central London, no trees around v. leafy suburbs), is it the construction of the flat? I read here in the forum that cavity wall/insulated wall/single-brick wall would make a difference, but my latest flat is cavity wall and very high humidity, higher than my previous single-brick wall flat.

Thanks!

Leo

motherofstudents

There is general atmospheric humidity like you see on some weather forecasts and then there is the humidity in a house/flat. The internal level of humidity can be changed by the way the property has been built, insulation and so on.

The only thing you can do is try to reduce it. You could try a dehumidifier, keep ambient temperature around 20C and ventilate well. Vaccuming your mattress will help. I'm sure someone will know more than I do though.

LeoC

Thanks, I should add that Flats 1 and 3 were both top-floor flats and Flat 2 was 1st floor flat, so no ground humidity coming up (which I guess could be a driver).

I use a dehumidifier, but for the flat/house that I want to buy, I was wondering if there is anything I could look for to keep humidity down even before needing to turn the dehumidifier off.

G_M

The main cause of internal humidity is lifestyle. Humidity is water suspended in the air. Where does water vapour come from?

Hot Showers. Baths, washing machines and esp dryers that do not vent externally. Cooking. In other words any activity that produces steam/hot water. This rises into the air and stays there unless....

It has somewhere to escape eg open windows, extractor fans

So:
a) cut down on the amount of water vapour by covering saucepans etc when cooking, venting thr dryer externally, not leaving wet washing to dry inside
b) remove water vapour from the air via windows, extractor fans, air conditioning and humidifiers

phill99

The levels of humidity are dependent on, primarily, 2 things: your lifestyle and the construction of the property.

Humidity is a measure of the amount of moisture in the air. This moisture is created by us in our homes. Some comes from our breath and we can't do much about this. But most comes from our daily activities: bathing, showering, drying clothes, cooking. To reduce the amount of moisture in the air in your home you need to reduce the moisture caused by these activities. :

When you shower or bath ensure you have extractor fan in your bathroom and use it. Let it run after you have finished in the bathroom for a good 30 - 60 minutes to get rid of the steam. Also, once you have finished in the bathroom, open the window and keep the door shut. This will ensure the steam is kept in one room and goes out of the window, and not into the rest of your flat. If you bath, put cold water in before the hot as this minimises the amount of steam generated.

Avoid drying clothes round the flat, again to minimise the moisture in th air.

When cooking pasta, veg, rice tc, always have a lid on the pan. Ideally, have an extractor fan on or at least own the window.

So essentially you are trying to minimise the amount of moisture in the air, and when it is produced, you are trying to get rid of it by means of mechanical extraction.

Poorly insulated homes tend to have higher levels of humidity as they allow the production of condensation on either the windows or walls. The condensation is another source of humidity. Therefore if you have double glazing and cavity wall insulation, it minimises the chanc of condensation forming. However having the windows open slightly will help get rid of moist air an allow cool air into the house. Cool air holds less moisture than warm air.

Not aware that the actual location of the hoe in London will affect its humidity.

motherofstudents

We have a very powerful centrifugal extractor in the bathroom and a decent one in the kitchen which you might want to think about as they do really make a difference.
As above, the main thing you can control is lifestyle. The moisture in the air will gravitate to the coldest part of the flat, usually windows in the coldest room but also cold walls. Hence the need to keep the flat well heated.
Do try to use a dryer to dry your clothes.

CLAPTON

I would disagree with many of the comment here

humidity is indeed a function of the amount of water vapour in the air AND the temperature
so for any given amount of water vapour in the air the hotter it is the lower the humidity, the lower the temperature the higher the humidity

the weather is clearly a major factor; when it's raining humidy outside is very high

inside your house it depends on the weather and a lot on how you live

usually well insulated houses have major problems will high humidity often seen as mold around windows

basically, reducing the amount of stream as already mentioned, extractor fans (after a shower/bath/cooking use the extractor for at least 4/5 hours

and keep the place warm

LeoC

Thanks for the tips. We haven't cooked the whole week this week at home, so no steam from the kitchen. I guess any steam we produce is coming from hot showers, we do shower with the bathroom door closed and window open, but there is still quite a lot of steam. I don't think that the extractor in the bathroom is doing anything at all.

Also I believe that our new flat was empty for months before we moved in, at least 2 months, probably more. It was also recently refurbished and smells a bit like paint. So perhaps because it was not heated for a while (and therefore cold inside) together with potential replastering of the walls (always a wet business) perhaps it made the fabric of the flat humid, and we need to suck this humidity away with the dehumidifier?? And then afterwards it will go down? (we hope).