The perfect breathable damp and condensation free house

[JoceAndChris]

Mmm, me too.

I have noticed that I feel the cold a lot less since putting on a bit of weight. Obviously it isnt good to be overweight but my skinny friends really can't cope with the draughty cold here, whereas I'm wrapped in a snuggly blanket of flesh, and can't bear a stuffy room or hot temperatures anymore. If the house is damp open the window and get out the scones and clotted cream!

 

[Penners]

I'm wrapped in a snuggly blanket of flesh

Well, it's certainly getting quite warm in here.

Or is it me?

 

[worms]

As has beenpointed out, sometimes you can let in high humidity warm air (e.g. with the arrival of a warm front in the autumn) when the interior of your house is at a lower-than-outside temperature. Then condensation will be widespread. Think on this before opening the cellar door to 'dry it out' on a warm day. The best drying weather is when its icy cold - it was noticable in the cold snap last Dec/Jan that our internal woodwork was shrinking due to the very low humidity.

Absolutely! All the wood here swells up and the mould forms in summer when all the windows are open all the time but the outside is often warmer than the inside. Last winter saw the lowest RH levels I've ever found in the house, despite all the cooking and drying going on and us being home all day over Christmas.

 

[CliffordPope]

It is also worth pointing out that the water content of air roughly doubles every 10 degrees increase in temperature. i.e. if it is raining outside with 90% humidity and 10°C temperature then this same air when brought into the house and heated to 20°C will have a humidity level of roughly 45%. This is how cold air from outside which is circulated through your heated house will help remove the moisture.

But it hasn't removed the moisture, it is still there in the air. The relative humidity is just that - relative to how much moisture the air could hold at maximum. The air may now be at 20 degrees, but the walls won't be, certainly not in our unheated upstairs. As I said, the walls will be at the average of day and night time temperatures, ie less than 20 degrees.

The water content of air doesn't double every ten degrees, it's its ability to hold water that doubles.

 

[Penners]

It is also worth pointing out that the water content of air roughly doubles every 10 degrees increase in temperature. i.e. if it is raining outside with 90% humidity and 10°C temperature then this same air when brought into the house and heated to 20°C will have a humidity level of roughly 45%. This is how cold air from outside which is circulated through your heated house will help remove the moisture.

But it hasn't removed the moisture, it is still there in the air.

Quite so, which is why I keep banging on about ventilation.

 

[CliffordPope]

But you were talking about outside air at 90 % relative humidity. I don't see any point in letting in some more damp air, just because it is called "ventilation". If mild damp air from outside finds a cold wall, it will condense. The house air might be at 20 degrees, but the walls won't be.

 

[MdB]

The water content of air doesn't double every ten degrees, it's its ability to hold water that doubles.

Yep, that was what I was trying to say. I should have been clearer.

But you were talking about outside air at 90 % relative humidity. I don't see any point in letting in some more damp air, just because it is called "ventilation". If mild damp air from outside finds a cold wall, it will condense. The house air might be at 20 degrees, but the walls won't be.

If the walls inside are colder than the air outside then you are correct, condensation will occur, but I find that unlikely. For most people the walls will be warmer than the outside air - otherwise there is no point in having any wall insulation.. The larger the temperature difference the better the moisture transfer but even a small difference will help. Remember also it is a two stage process, first there is a transfer of air into and out of the house. With colder air outside, this transfer will cause moist warm air to leave and dryer colder air to come in. Secondly the hopefully dryer warm air inside will pick up moisture from the wall. The outside air won't in general pick up moisture directly from the wall and then leave.

 

[AMc]

I suppose that is the issue - where is the tipping point between ventilation and draughts

IMHO
Draught - unplanned movement of air from outside in or inside out which may or may not remove moisture, stale air & heat etc.
Ventilation - planned movement of air from outside in or inside out which does remove moisture and stale air with minimal loss of heat.

I have a ventilation fan in the bathroom and a draught around the warped back door which I don't know how to deal with.

My electrician tried to convince me to install a Mechanical Ventilation & Heat Recovery system during our renovation
http://en.wikipedia.org/wiki/Heat_recovery_ventilation

While we don't have damp or condensation problems it would have made sense as we have a large solar gain in the vinery which it would have been nice to distribute to the older, colder part of the house. It would also have allowed me to dispense with the extractor fans and trickle vents recover their heat loss. However I have a nasty suspicion it would have been a bat magnet in the summer and would have neatly distributed the smell of bat wee from the loft so perhaps not a great idea in this particular house

 

[Penners]

Draught - unplanned movement of air from outside in or inside out which may or may not remove moisture, stale air & heat etc.
Ventilation - planned movement of air from outside in or inside out which does remove moisture and stale air with minimal loss of heat.

:lol: :lol: Well put!

The need for ventilation can be a great boon to the bone idle DIYer.

Her: "Can't you please do something to stop these awful draughts?"

Him: "Stop them?! Don't you realise just how vital the ventilation is to the health of this old building?"