Condensation and mould in bedrooms

[benny moo]

Fair play. I'll also ask the ventilation companies about dMVHR systems. The issue only occurs in the two bedrooms. It's quite outstanding there is no mould in the lounge, kitchen and bathroom so a dMVHR in each room might be an option.

 

[noseall]

I’ve been dealing with cold walls in a couple of bedrooms due to having two external walls, which causes cold areas and has led to issues with condensation and mould. This is something I’ve always experienced with the property, even after living here for over 10 years.

I’ve involved the council several times, and they carried out a building survey, concluding that there isn’t any rising or penetrating damp occurring externally. They also provided the following information about the building’s structure:

“Having now looked at the structure, I can confirm it’s a typical late-1950s low-rise structure with solid external walls under a timber pitched roof, similar to many builds of the post-war period. One of the fundamental issues with such builds is that there is no thermal break between the inner and outer-faced brickwork, allowing cold to penetrate. Most modern brick builds of this type have a cavity between the inner and outer walls, which allows for insulation and helps prevent cold bridging and heat loss.”

I’m now considering one of two approaches to address the issue:

Installing humidity-controlled thermostatic extractor fans in the bedrooms. While effective, this could look out of place aesthetically. I know other properties nearby have had trickle vents installed, but they don’t seem to make a significant difference. Would extractor fans help manage high humidity and condensation effectively?

Fitting PIR insulated boards to the two external walls in each room to reduce the cold areas and minimize cold bridging. However, I’m concerned this could potentially make things worse by shifting condensation to the next coldest surface. Is this a valid concern?

In the short term, I’ve been promoting good airflow and using a dehumidifier to manage the humidity levels while deciding on the best course of action. Any advice or insights would be greatly appreciated.

You need to insulate the walls and also look at mitigating the build-up of condensation as best you can.
Mechanical and passive ventilation also needs to be considered/fitted.

Telling folk not to generate moisture, is as silly as it is pointless. Telling people not to put things against the walls - equally as stupid.

 

[noseall]

Add stud wall insulation with an air gap, to retain heat and reduce the cold bridging. Turn your heating up, and use a dehumidifier.

Insulation can be fitted directly to the masonry, if space is an issue.

 

[noseall]

Don’t pile stuff up against walls, open the windows regularly.

Lol.

 

[stuart45]

There's a method in Germany called Stobluften where they open all the windows for about 20 minutes first thing in the morning. The idea is to get a massive blast of dry, fresh air into the house.
I used to see all the windows open and duvets hanging out to air going to work at 6:30 in the morning, along with all the kids off to school.

 

[Mottie]

There's a method in Germany called Stobluften where they open all the windows for about 20 minutes first thing in the morning. The idea is to get a massive blast of dry, fresh air into the house.
I used to see all the windows open and duvets hanging out to air going to work at 6:30 in the morning, along with all the kids off to school.

Mrs Mottie must be part kraut then. If she had to have a 3 word slogan it would be ventilate, ventilate, ventilate. She even whips the duvet off the bed to let that air for at least an hour before making it and piling 101 cushions onto it.

 

[noseall]

Mrs Mottie must be part kraut then. If she had to have a 3 word slogan it would be ventilate, ventilate, ventilate.

Ventilating is great - if you are able. Building design and designers, believe it or not, have to look at those that are unable to leave windows or doors open, for what ever reason. I'm guessing not everyone lives in posh Essex.

 

[Mottie]

Ventilating is great - if you are able. Building design and designers, believe it or not, have to look at those that are unable to leave windows or doors open, for what ever reason. I'm guessing not everyone lives in posh Essex.

Feck me, if you’re living in an area where you can’t leave a window open, a bit of mould would be the least of your problems.

 

[Ivor Windybottom]

Thanks I've been looking at MVHR and PIV systems before I even posted this.

It's a single floor flat with no loft so perhaps the Nuaire Flatmaster is what I need.

Don't. Fix the problem itself instead of finding workarounds.

Excessive ventilation may reduce condensation, but at the expense of even higher bills. Taking ventilation to the extreme, if you knocked down the house and lived outdoors then you'd definitely have no damp issues.

Heat recovery recovers some of the heat - 50% at an absolute theoretical maximum, in practice much less. It will cost you more to keep the same level of heat.

You need insulation between your living space and the outside air. There isn't a quick fix simple answer.

 

[Ivor Windybottom]

We also ventilate every morning. Seal up at lunchtime, heat in the afternoon.

Both of our work rooms are heated separately while the wind is blowing through the rest of the place.

 

[robinbanks]

50% at an absolute theoretical maximum

Nonsense

Fix the problem itself instead of finding workarounds.

Controlled ventilation is a solution, not a workaround

 

[Ivor Windybottom]

Nonsense

Good to see such in-depth thought going on.

So... the inside air is 20 degrees, the outside 0 degrees. The incoming fresh air passes through an ideal (i.e. better than reality) heat exchanger, where the heat from the extracted air heats up the incoming air. What temperature do you think this incoming air will end up? The answer is that the temperatures will (roughly) average. The incoming will be 10 degrees, as will the outgoing. You can't ask physics to make the outgoing air colder than the incoming, it just doesn't work like that.

In reality it's nothing like this good. The incoming air might be 5 degrees, the outgoing 15. Heat gets wasted even in the absolutely impossible best case scenario.

It's much better to fling the windows open once a day, before the heating comes on, change all the air then seal up and heat it.

 

[Ivor Windybottom]

Some small amount of ventilation is best. Trickle vents on windows are good. They allow a small amount in, particularly useful when an extractor elsewhere in the house is running.

Obviously this is at the expense of efficiency, but it's a good compromise. Around the windows is a good place to have incoming air, as it's where condensation is likely to gather and, at night, it will be behind the curtains.

 

[endecotp]

So... the inside air is 20 degrees, the outside 0 degrees. The incoming fresh air passes through an ideal (i.e. better than reality) heat exchanger, where the heat from the extracted air heats up the incoming air. What temperature do you think this incoming air will end up? The answer is that the temperatures will (roughly) average. The incoming will be 10 degrees, as will the outgoing. You can't ask physics to make the outgoing air colder than the incoming, it just doesn't work like that.

I used to think that, until I realised how it actually works. The crucial point is that the fluids in heat exchangers flow in opposite directions to each other. E.g. say the outgoing, cooling, air flows left to right and the incoming, warming, air flows right to left. Here's a terrible attempt at a diagram:

Outgoing ---> 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
Heat flow v v v v v v v v v v v v v v v v v
Incoming <--- 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

At the right end, the outgoing air at 2C transfers a bit of heat to the incoming air at 0C, and they both end up at 1C.
Immediately left of that, the outgoing air at 3C transfers a bit of heat to the incoming air at 1C, and they both end up at 2C.
......
......
At the left end, the outgoing air at 20C transfers a bit of heat to the incoming air at 18C, and they both end up at 19C.

So a theoretical heat exchanger really can be 100% efficient. In practice, as I understand it, the limit on efficiency is determined by the additional energy needed to pump the air through the constrictions of the exchanger.

 

[Ivor Windybottom]

I get your point, and it's an interesting idea but I very much doubt it works anything like that efficiently.

I'd like to see some proper measurements, I'd bet that 50% is a dream.

In practice you'd need a vast array of tiny orifices for the air to mingle with. Which would become a horrible dust-filled spider hotel in about a month.