New mould issue.

banie01

Hi folks, I have a relatively "new" mould problem in a house I've lived in for 18yrs. It's confined to 1 bedroom. The external wall and part of the ceiling are getting it recurrently at top of wall, junction of ceiling.

The house is an 80's built Semi-D with pumped wall insulation added, along with recent triple glazing. There is a vent in the bedroom. Overhead the bedroom is covered by 300mm of rock wool, with adequate venting at the eaves.

The bedroom's window is quite large and north facing, and on the affected wall(as is the rad). I'm thinking that the cold bridging and mould is likely due to insufficient pumped above the window compared to the rest of the wall.

What's the best method of dealing with this?

I'd prefer a permanent fix, rather than clean and repaint with anti mould added

10-10-20

Hi!

If the top of the wall cavity was closed with a block on it's side then that becomes a cold bridge at the wall/ceiling junction. You can measure the depth or extent of the cold area and that would give you can indication whether it's the cavity closing block or not (is it the depth of a block-on-side).

If you're not planning on installing IWI in the affected rooms then in my mind you're resigned to managing the humidity in the room/house to prevent the condensation at that point as there is no other realistic way to mitigate. I use a dehumidifier in my house to achieve that management of the RH.

DC999

https://www.boards.ie/discussion/comment/121588185#Comment_121588185

What's an IWI?

10-10-20

https://www.boards.ie/discussion/comment/121588232#Comment_121588232

Internal Wall Insulation - insulated plasterboard and such.

banie01

https://www.boards.ie/discussion/comment/121588185#Comment_121588185

Thanks for that. I'm beginning to think that the problem is a result of the triple glazing. where previously humidity would condense on the internal pane of the old double glazing, now its hitting upper wall and ceiling as coldest points in the room. My plan now is to squeeze into the eaves and see if cevity is closed at top of wall. I may well also run an extraction dusk into the corner of the affected bedroom.

micks_address

Do you have trickle vent position on your Windows? I've found in our house if we leave the bedroom windows open a crack in cold weather there's no condensation on the inside in the mornings..closed and they are soaking wet. I hoovered them with a karcher window vac one morning last week and a lot of water came off. I know it's cold so we close the windows till just before bedtime and then open them a little. Seems to make a big difference. We only have double glazing and it's on the cards to change the windows in next few years as they are getting on and have broken handles etc.. I was thinking of going triple glazing for the sound insulation more than anything else

banie01

https://www.boards.ie/discussion/comment/121608656#Comment_121608656

There is a trickle position alright, only issue with that is that its my son's room and he has a habit of locking them. its a good solution tho. In regards the sound muffle with triple glazing, I live in a quiet cul de sac on a very quiet estate and they are honestly like noise cancelling headphones, they've also made a big difference on our heating. The windows were the last part of the house's envelope we upgraded, after walls, attic, new gas boiler but they made a significant difference over the old leaky double glazing

10-10-20

https://www.boards.ie/discussion/comment/121608622#Comment_121608622

It's not the "fault" of the triple-glazing, per-say, you probably just had better incidental ventilation with the older windows which has now been eliminated. You possibly now have more humidity in the air on average than in the past, and the dew-point (temperature point where water condenses) has now risen so that you have more humidity in the air and it's more inclined to condense on cold surfaces. It's a feedback-loop of sorts.

After many years of hearing the answer of "increase the temperature of the house to reduce the mould" (which isn't in itself incorrect but goes against many of our heating habits here in Ireland) I've decided that a dehumidifier is the best option for many homes. Hence I have two dehumidifiers now (2001 build) and they come on-and-off as needed and keep me in-and-around 60% RH.

banie01

https://www.boards.ie/discussion/comment/121608740#Comment_121608740

That's precisely what I'd meant when I assigned the blame to the windows, you phrased it far better than I. As I improved the fabric of the house, the dew point moved away from the window.

I have a small dehumidifier that I can stick in there for the time being that will hopefully arrest the problem.