Bloody humidity meter!

[yamin]

A friend gave me a little gadget that measures relative humidity in rooms but I'm wondering whether to chuck it out! It won't drop below 66% reading at 13.5 degrees C or so in our bedroom. I'm removing woodchip at mo and wondered if it was the steamer, but not done any stripping for 5 days now and still obstinately at 66%. With woodchip off, presumably more air can get to the room. There was the odd bit of damp behind the paper, but not to my mind especially bothersome. The window is horrible double glazed plastic. Opening it as much as poss but we are by a busy road so can't have it open at night.
We are coming out of winter now (apparently) so no heating, but even in depths of, we avoided heating as I hate a hot bedroom.

Wondering firstly if the damp conditions over the last few days, and colder temps, have simply meant that the humidity can't escape, even out of open window

Secondly, if we are not bothered by damp or discomfort, can we ignore this kind of reading?

We cannot afford any kind of decent de humidifier. We have a ceiling fan, if thats any good!!

 

[worms]

Yamin, don't throw it out just yet! I thought the same when I first got a humidity meter and subsequently a dehumidifier. Our house rarely drops below about 64%RH without heat and/or dehumidifier and is very dependant on the humidity outside. Summer is the worst as the heating is off and the outside humidity rarely drops below the mid 60s. That is when the doors swell up! Lowest figures were during the Jan/Feb cold snap where at 11.5C, the bathroom was showing 48% RH but at times last summer it stubbornly sat at 84% even with the window wide open.

 

[johnandrew]

Hi Yamin

I spent a few months last summer measuring RH in my cellar. The temperature rarely deviated from 13 degrees celciius and the RH varied between 80% - 94%. I'm no expert but here is my understanding of RH and related matters.

My understanding is that RH is simply a measure of how much water vapour the air contains as a percentage of how much it can hold at that given temperature, pressure, etc. The higher the temperature the more water vapour the air can hold before reaching saturation point.

Your bedroom at 13 degrees has a RH of 66%. But the RH at 18 degrees would be 48%. The amount of water vaopur in the room would be the same in both cases.

I'm sure others will correct me if my thinking here is wonky.

This site is quite useful: http://www.humidity-calculator.com

Regards

John

 

[Andrew Bodenham]

Yamin,

Whilst it can be useful and interesting to be able to quantify things like humidity it is really the qualitative analysis that counts, viz. "does it feel damp in here?"

If it feels damp enough for you to worry about it then add some heat, and ventilation. If not, don't worry.

My workshop where I make furniture is a bit damp, despite having a dehumidifier running 24/7, and I have real problems with pieces of furniture that I've made shrinking or curling up when I take them into client's modern dry houses. Give me a nice damp house any day.
(who remembers Fungus the Bogeyman......?)

 

[worms]

Your bedroom at 13 degrees has a RH of 66%. But the RH at 18 degrees would be 48%. The amount of water vapour in the room would be the same in both cases.

Yes, but the RH is only a measure of the moisture in the air in the room at a given time. The difference between your two scenarios above would surely have a big effect on the extent to which condensation might form on the walls or the previously damp walls dry out (or indeed on the moisture levels in my doors!).

I found that using a humidity meter around the house helped me to understand what is going on in terms of moisture much better, including the effects of the central heating (not just the heat allowing cold air to warm up and carry off more moisture, but also the huge amounts of damp air that the Rayburn sucks out of the kitchen when it is running).

As part of an "old house learning curve" I'd recommend a humidity meter to anyone!

 

[yamin]

My understanding is that RH is simply a measure of how much water vapour the air contains as a percentage of how much it can hold at that given temperature, pressure, etc. The higher the temperature the more water vapour the air can hold before reaching saturation point.

Your bedroom at 13 degrees has a RH of 66%. But the RH at 18 degrees would be 48%. The amount of water vaopur in the room would be the same in both cases.

To my shame this is shaking my old and inadequate brain cells a bit! But are you sayingn that at 66, the air in the room is only holding approx 2 thirds of the moisture it could actually absorb?

The difference between your two scenarios above would surely have a big effect on the extent to which condensation might form on the walls or the previously damp walls dry out (or indeed on the moisture levels in my doors!).

This is what I am thinking, or my concern - less about how the air feels and more about should I worry about the permeability and/or damage to the walls?

If it feels damp enough for you to worry about it then add some heat, and ventilation. If not, don't worry.

This is what I was hoping to hear and what my gut feeling was telling me too, though I do want to understand it (hence questions above!), but yes, I'm tending to think if it feels ok it is OK. I just don't want to rislk damage/paper off walls etc.

(who remembers Fungus the Bogeyman......?)

Daily reminded of the old chap, together with Mould, Mucus, Mildew, Grot, Gunge, Septic etc - a favourite story CD in our car!

 

[JoceAndChris]

Well I think you're very brave getting one of those machines up and running - I wouldn't! When the nasty Damp Men came here with all their metres and gadgets they said the bedroom was damp, the humidity was high, and the plaster needed hacking off the walls and a long drying out period to ensue. They said that even though evidence of damp was limited to a very old woodworm infestation. The paper wasn't peeling off the walls, there was no condensation on the window, and no smell of damp. But we believed them, until reading everything on this forum convinced me that damp can only be properly assessed with the eyes and the nose. We had delayed decorating until this revelation but then thought sod it and decorated.

It's April now (yay!), it's been a long, cold, wet winter and spring and there's no damp in the bedroom- the new decorations are all fine.

I wouldn't worry about not having a dehumidifier either - we've got one and I'm putting it out in the shed. It sent my pamment floor downstairs completely white. Now I've switched it off, the efflorescence is crumbling off and the orange colour is returning.

I really wouldn't let that device bother you too much. Decorate, and have the window open in the summer when you can.

 

[Merlin]

I can second the view that using your own senses is a good method to detect damp. Our kitchen was damp when we moved in; it smelt damp and it felt damp.

We replaced a broken drainpipe and refitted other drainage pipes on the outside wall, all of which were "splashing" onto the wall. I have started to knock the cement render off the back wall at the bottom (manually with hammer and chisel.) There is no sign of a chemical damp course yet! The wall is now visually much drier to the eye, and feels dryer to touch - it no longer has that cold clammy touch.

The kitchen now does not smell of damp - nor feel damp, even though it is sometimes cold in there. We also have less visitors (woodlice) who I believe prefer damp areas to dry areas.

We will keep monitoring it to see how it goes, but at the moment things are looking / feeling / smelling positive.

 

[yamin]

These are both very encouraging replies - thank you. I agree wholeheartedly that nose/eyes/sense/comfort a much better indicator of damp, or should I say, problem damp. Its just that sometimes people who believe strongly in 'their own way' can shake your confidence a bit!
Well, I shan't worry then, and continue with the decorating and the open windows!

 

[JoceAndChris]

Go for it - that sounds very sensible to me.