Condensation on cold walls - what can I do?

Fastmower26

Hi all, I have had a search through the forum and found a few old threads but nothing recent. I have a Victorian end of terrace house. I am getting condensation on the cold walls in the bedrooms.(teenagers spend a lot of time in there with door closed, as teenagers do) It had created mould and I was constantly cleaning the walls. I did paint bathroom paint on one wall to see if that improved it. It did stop the mould but now the walls are actually wet and need wiping with a towel.  They are not cavity walls so does not have cavity insulation. I was wondering what I can do to stop this happening.  Would insulation board like kingspan help. And if so does it go straight on wall, or leave an air gap on a timber frame? Or do I fill the air gap with like loft roll or something?  I have even looked at that thermal paint, but I don’t think that will be enough? Any advice, or people’s experiences of similar would be much appreciated, thank you

Martin_the_Unjust

Ventilation will be the key, if the rooms are occupied with the doors and windows shut you need somewhere for all the moisture a person expels to escape.

Insist on a window being cracked open while they are in there and that they leave the door open while they are not.

aoleks

Ventilation indeed, insulating the wall (your type of wall) will only make it much worse. It’s not the wall temperature that’s the issue, but the extreme levels of humidity in the house/room.

grumbler

Fastmower26 said:

 Would insulation board like kingspan help. And if so does it go straight on wall, or leave an air gap on a timber frame? Or do I fill the air gap with like loft roll or something?  I have even looked at that thermal paint, but I don’t think that will be enough?

I've never heard of of thermal paint, but am pretty sure it's all lies.

Insulated plasterboard with 50+mm of insulation will make a huge difference. Normally it's screwed to batons screwed to the wall.

And do you realise that big, if not biggest part of the moisture in a house is often produced by gas burning in a hob?

RAS

Get the end wall checked in case it needs re-pointing so you have penetrating damp as well

Check juniors' life style? Do they drape wet towels over the radiator etc?

In the short-term, rotate a decent de-humidifer  between the rooms and tell them to leave the doors open when they are not in.

Think about the moisture created by bathrooms and the kitchen, is this dealt with "at source"? A squeege makes it much easier to dry a shower area for example; then ventilate for an hour.

FreeBear

RAS said: Get the end wall checked in case it needs re-pointing so you have penetrating damp as well

And the wall does need repointing, use a lime mortar, not cement.

Bathroom paint would have been the wrong stuff to use, especially if you have the original lime plaster on the walls - Bathroom paint leaves a waterproof plastic film on the plaster which stops it from absorbing & releasing moisture, but hey ho, the damage is done...

What I would do (and have done) is remove all the plaster from the wall. Fix vertical battens (25x50mm) to the wall with a strip of DPC between the battens & brick (~600mm centres). Cover with 25mm Celotex, sealing the joints with expanding foam and aluminium foil tape. Put some horizontal batten on, screwed through the Celotex and in to the vertical battens, again at 600mm centres. Fill the space between the battens with more Celotex, again, sealing with foam & tape. Finish off with plasterboard, and skim. A thin layer of Celotex needs to be fitted around the window reveal, but you can get away without an air gap behind it - This will limit any cold spots forming in that area.

If the radiator is fixed to the wall under a window, consider having it moved to an internal wall. With modern double glazing, there is no real need to have radiators under a window.

The above work will cost something in the region of £200 for materials, and maybe £300 for a plasterer to do the final skim.

If money is an issue, slap some Wallrock thermal paper (other brands available) on the wall. Whilst it won't do much to insulate the wall, it should help to reduce condensation a bit. It will also trap damp behind (as will the bathroom paint), which may cause problems in a few years time.

Edit to add - Insulating the walls as described above will have two advantages. An improvement of the EPC rating. A reduction in heating bills as well as making it easier to heat the (insulated) rooms. Condensation will still be an issue, but it will be limited to the window, so should be easier to manage.

youth_leader

I came on here earlier in the year because my bedroom windows were dripping with condensation, and I bought an Aldi 20L dehumidifier.  The door has to be shut during use and the windows were clear in the morning, it collected about 10L per night.

It seems the bungalow doesn't have enough ventilation as both chimneys have been boarded up/blocked, and some of the double glazing doesn't have trickle vents.  I've started leaving all of the windows open a 'crack'.

The surveyor recommended I get a positive ventilation system installed in the loft that will work for the whole bungalow, rather than just one humidifier in one room.

(Since then I have found out the floorboarded front bedroom has wet/dry rot and woodworm!  And the weyroc in the other two bedrooms is black and mouldy, the surveyor said water is somehow getting underneath the building.) 

neilmcl

Consider a PIV system. These can work wonders for older houses with condensation issues.