Condensation and mould in bedrooms

[endecotp]

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

Google will find you a range of numbers. I don’t have any personal measurements to share, but I think you could expect 75% or more.

Still, these things are expensive. It’s clear that they are more useful, i.e. give better return on investment, in climates that are more extreme than the UK, e.g. Canada, Sweden.

 

[Harry Bloomfield]

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.

I used to believe that, seemed logical, but no - much better than 50%

 

[Ivor Windybottom]

Wikipedia reckons 80% is achievable. If this is actually achievable it's pretty impressive.

 

[Ivor Windybottom]

I apologise to the gods of MVHR and consider myself a new disciple. Won't buy it though, would much rather have a burst of fresh air in the morning before the neighbours start setting fire to stuff.

The outside air is probably more polluted than indoor in many places in an evening, thanks mainly to the wood burning trend.

 

[Harry Bloomfield]

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.

If you cannot persuade your landlord to tackle it properly, could you get permission to tackle it yourself. How difficult would it be to add studs to the wall, insulate between them, then plasterboard over? Do one room at a time.

 

[robinbanks]

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.

Countercurrent exchange - Wikipedia

en.wikipedia.org

In practice you'd need a vast array of tiny orifices for the air to mingle with

The fluids on either side of a heat exchange don't mix..

Won't buy it though, would much rather have a burst of fresh air in the morning before the neighbours start setting fire to stuff.

A house well set up for MVHR does permit this too; they work best when they are the sole control of ventilation, which means no gaps, cracks, drafts, trickle or extract vents that do not close fully when inactive. As such, when you turn the unit off, you don't get the neighbour's wood burner output

 

[Ivor Windybottom]

You know what... I'm going to look into MVHR, it seems like a sensible option. Very useful to have a constructive debate and glad to be wrong.

But I'm still of the opinion that it's something you add on top of decent all-round insulation, not an alternative to it.

 

[Roberto2019]

PIV and a log burner... sorted. You'll have a lovely warm house, constantly flushed with clean air, and will never see mould again.

 

[robinbanks]

But I'm still of the opinion that it's something you add on top of decent all-round insulation, not an alternative to it.

Totally; insulate tight, ventilate right. You'll probably find all aspects of passivhaus construction interesting - I was once amazed at the notion that we can construct houses that need no formal heating system at all, just by getting the science right. Now it seems more obvious, because I can recognise so many places the average house loses what could be preserved through better construction detailing. Very few builders care to be so precise, beyond self builders doing it for their own gains

 

[noseall]

I can recognise so many places the average house loses what could be preserved through better construction detailing. Very few builders care to be so precise, beyond self builders doing it for their own gains

After many years of dealing with 'damp' complaints from various clients and their varying property ages, I have a much better understanding of how to deal with issues arising from external cold and internal condensation. Door and window reveals, raked ceilings, window bays, NE facing alleyway walls, kitchen, bathrooms etc, all have their condensation risk idiosyncrasies.

There is nothing better than a good thick slab of well taped/sealed, foil sandwich PIR, for sticking it up to black spot mould.

 

[Ivor Windybottom]

We have a north facing wall that's always cold. Before we bought the place it got mouldy. We dehumidify and ventilate once a day and have no issues.

The problem with solving condensation with insulation is that the cold surface was actually acting as a dehumidifier. That damp won't condense here any more so will just find the next coldest surface to stick to.

You need to start with the water source. Usually extractors in the bathroom and kitchen will eliminate most issues. Suspended floors will normally allow enough air in for extractors to work. But with solid floors you need trickle vents in other rooms and gaps under the internal doors so that air can be pulled through the place by the extractors.

Drying washing indoors is just a recipe for mould. We used to do it, until we got a heat pump dryer which we use for about 99% of washing. It costs almost nothing to run, and all that water ends up down the drain instead of in the air.

 

[Harry Bloomfield]

We have a north facing wall that's always cold. Before we bought the place it got mouldy. We dehumidify and ventilate once a day and have no issues.

Our end wall, of our semi is north, north west facing. We never open windows in the cold weather, never suffer mould, or damp. Apart from a tiny, mysterious 12" wide section of rising damp, in a brick wall, dividing the back of the toilet, from the under-stair cupboard.

The problem with solving condensation with insulation is that the cold surface was actually acting as a dehumidifier. That damp won't condense here any more so will just find the next coldest surface to stick to.

You need to start with the water source. Usually extractors in the bathroom and kitchen will eliminate most issues. Suspended floors will normally allow enough air in for extractors to work. But with solid floors you need trickle vents in other rooms and gaps under the internal doors so that air can be pulled through the place by the extractors.

Drying washing indoors is just a recipe for mould. We used to do it, until we got a heat pump dryer which we use for about 99% of washing. It costs almost nothing to run, and all that water ends up down the drain instead of in the air.

All spot on! Except, rather than a heat-pump drier, we use a dehumidifier, a fan, and lines in the utility, to dry washing. We washed a full load of mixed items yesterday afternoon, along with a pair of large lounge curtains. All hung up in the utility, with the door closed, fan and dehumidifier running for 6 hours. All dry, by 10pm, at an average cost of 75w.