mould on walls and celing in bedroom

Found_true_love

matty2767 wrote: »

we moved into a new build 5 yrs ago and every winter since we end up having small spots of mould in the corners of the bedroom. it starts about midway up the wall and continues a little way onto the ceiling. i guess the corners dont get a free flow of air but we have the trickle vents open all the time. i can get rid of the mould by wiping with mould remover but eventually it does come back again until the summer when the air is drier. does anyone have any ideas as to the cause of this?

thanks

matthew

Ho hum the history of condensation in buildings

The explanation of how condensation forms on walls (or any surface)

Air, at any given temperature, has the ability to hold water vapour the warner the air the more vapour it can hold up to its saturation point reletively speaking of 100%. So air at 30degC can hold more water vapour that air at 20degC.

So air with a relative humidity (RH) of 50% at 30degC is actually holding more actual vapour (in grammes of vapour per m3 of air) than air at 20degC 50% RH.

Now all vapour in air has a corresponding dew point for its given temp and RH. So when the air vapour mixture comes into contact with, say a wall, at its critical dew point temp then the vapour cannot be held in the air any longer and it falls out of its air onto the surface as condensation.

So with us heating our homes to 20degC in the winter months and the wall temperatures being colder (not much but relatively speaking enough) condensation forms on internal walls. It could actually form inthe fabric of the structure itself (as interstitual condensation) which is why we have vapour barriers in cavity walls now, and insulation that is not degraded by moisture.

So the history, years ago we had leaky draughty houses (caves first, then huts, then castles, then......) all those types of habitat we didnt notice cos they were so cold to worry about condensation.

Then we discovered single glazed draughty windows (sash type) that let all the air in and moistue out, the glazing was so cold all the moisture formed on the glazed panel and was easy to clean off.

Now we seal our houses, insulate them and do lots of very moisture generating activities, showers, cooking, breathing etc. moistue became a problem because we wanted to keep the house warm and letting cold outside air in did not seem very energy efficient.

Now we had a real problem with condensation, so now we deliberately let nasty cold outside air into our buildings with sneaky little openings called trickle vents. In theory letting in colder (thus holding less actual moisture) air to bring down the RH of the internal air thus making it less likely to reach the dew point.

But we still produce too much moisture in our houses all of the time.

So to resolve the problem house builders (through legislation) put in fans in the house in all areas that produce the nasty moisture, bathrooms, utility rooms, kitchens etc. and they also have trickle vents

The solution is PRODUCE LESS MOISTURE IN THE FIRST PLACE.

Ah cant do that can we?

Next we can turn the heating down a bit, that will help, it lowers the dew point that condensation will form. I.E. the wall would have to be colder for the condensation to form.

Ah but some members of the household are a bit too nesh (feel the cold)

Ah cant do that

The solution that seems to work (and it involves MORE ventilation is to put in an active positive displacement ventilation system.

Basically it is a fan system that is located in the loft, it takes loft air (partially warmed but dry(ish) because no one does any nasty moisture generating activities in the loft) and trickles it into the space, displacing the moisture ladened warm air in the house. The same moisture ladened air is circulated into the fans system via an air to air heat exchanger (takes out the energy from the warm moist air and puts some of it back into the house) and then expelled to outside.

Vent Axia, Nu Aire, Greenwood Airvac (to name a few) all do systems like this (I know Nu Aire do cos I used to sell them) they would cost in the region of £500 plus installation.

Condensation problem solved......

Or you could just wipe the mould away when it grows.

Hope this tale of "thermodynamics" helps (it took me ages to understand it)

An as it is sooo long since I studied the actual mathematics of dew point temps, vapour pressures etc there is probably a lot that I have forgotten

brig001

I would check the roof and gutters around these areas. You could have a small leak which wouldn't show up in summer - the heat would dry it out. I would also check your loft insulation in these corners - as has been said, you need cold and moisture to get condensation. Talk to your neighbours to see if they have the same problem.

HTH,
Bri.