Bathroom breathability

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Feltwell
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Bathroom breathability

Post by Feltwell » Tue 19th Oct, 2021 6:24 pm

Hello,

In the midst of bathroom renovations here - 2 bathrooms at the same time, just to make life interesting! Increasing the size of our stupidly small family bathroom by taking some space from the adjoining en-suite bathroom, so the wall between had to come down. New stud wall has gone in, plus a mix of knackered plasterboard and knackered lath & plaster has come off a side wall - it was well & truly beyond redemption - and has been replaced with Elements board, as these will in part form the back walls of a shower cubicle. I'm very impressed with Elements board - totally waterproof, lightweight, very easy to cut and feels very sturdy once up.

https://www.youtube.com/watch?v=QwlHR6rEduY

Which got me thinking - breathability. In the en-suite bathroom, the first one to be refitted, the Elements board has gone on internal stud walls only. There is an external wall, but it's not behind the shower cubicle - it's been gypsum plastered by previous owners but shows no signs of damp so will stay as is.

However - in the family bathroom, a bath with shower over will go in a corner adjacent to two external walls. Those walls are currently gypsum plastered and are cold - condensation & mould has been a problem. Ventilation will be massively improved in the refit (no fan at present), but these external walls will be fully tiled - surely a fully tiled external wall can't offer much if any breathability? I'm considering using the Elements board on these walls as well - give a much better surface to tile on and offer some insulation to help reduce condensation.

It seems wrong to be sticking an impervious board to the walls, but by the same token I can't see that there will be any breathability anyway - can anyone see a downside?

Walls are 9" solid brick, lime pointed on the outside, no sign of any damp - even though up until last year the pointing was fairly knackered cement.

Cubist
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Re: Bathroom breathability

Post by Cubist » Tue 19th Oct, 2021 6:54 pm

I was faced with the same conundrum a few years back when I modernised our master bathroom. Finally I decided that, provided the interior of the room was properly ventilated all I needed to be concerned with was condensation/evaporation from other rooms below and beside the bathroom. Provided there was adequate air movement opportunity in the floor and ceiling spaces I reckoned the overall impact of fully tiled walls in one room would be minimal.

worms
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Re: Bathroom breathability

Post by worms » Wed 20th Oct, 2021 9:34 am

Is the current gypsum plaster directly onto the brick? In the new arrangement, could the Elements board be mounted onto battens to allow air movement behind it? Is there space to allow for air movement and a little insulation? It sounds like this is an external corner of the house and these are often problematic in terms of both condensation and water ingress, so everything you can do to warm the inner skin and allow the outer skin to breathe would help.

CliffordPope
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Re: Bathroom breathability

Post by CliffordPope » Wed 20th Oct, 2021 6:23 pm

charlottmia19 wrote:
Wed 20th Oct, 2021 11:56 am
Plumbing air vents also prevent sewer gases from entering the home and allow wastewater gas and odor to escape.
I thought that was the function of U-bends, to stop gases coming in from the external drains, and of extractor fans to take internal odours (and steam) outside?

worms
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Re: Bathroom breathability

Post by worms » Thu 21st Oct, 2021 7:51 am

Clifford, the two posts from charlottema19 are sufficiently odd and disconnected from their topics to make me wonder if these are from some sort of auto-response bot. There is so much wrong with both posts, that I don't think it is worth rising to them.

Feltwell
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Re: Bathroom breathability

Post by Feltwell » Thu 21st Oct, 2021 9:45 pm

Yes, I got the impression charlottmia19 was some kind of bot. Who bothers to write these things?

Anyway, bathroom. At the moment it's a gypsum skim over the original lime plaster, partly tiled, partly plastic emulsion paint - so no breathability internally. Outside is OK now, lime pointed brick, but it was cement pointed up until last year and still no sign of damp, apart from condensation. Ideally I'd take the plaster off, batten and fix the Elements board with a ventilated gap behind, but there's really not much room to batten so I'm contemplating dot & dab the Elements board straight onto the brick - will still leave a tiny gap behind. Not very traditional but the Elements board will keep the bathroom water vapour out, even if the tile grout lets moisture through, and the foam core will give a little insulation to hopefully cut the condensation down.

Ventilation - there were just windows only, when we started getting mould problems I fitted a 4" wall mount fan with a humidistat - thinking then I don't have to rely on the family to remember to turn it on - that was a mistake, despite being an expensive and supposedly decent one it was hopeless, the humidistat never worked properly and it wasn't really powerful enough even for a small bathroom.

This time round it's an inline fan mounted above a false ceiling, supposedly a lot more powerful, drawing air in through a ceiling vent directly above the shower. The downside is the human element, it'll be switched on via a momentary "pull to make" ceiling switch, then run on a timer. I could link it to the lights but that always seems very wasteful to me, you don't always need the fan on. I'll just have to drill it into the kids to actually turn it on! :roll:

worms
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Re: Bathroom breathability

Post by worms » Fri 22nd Oct, 2021 7:54 am

Feltwell wrote:
Thu 21st Oct, 2021 9:45 pm
This time round it's an inline fan mounted above a false ceiling, supposedly a lot more powerful, drawing air in through a ceiling vent directly above the shower. The downside is the human element, it'll be switched on via a momentary "pull to make" ceiling switch, then run on a timer. I could link it to the lights but that always seems very wasteful to me, you don't always need the fan on. I'll just have to drill it into the kids to actually turn it on! :roll:
Will drawing outside ambient air, directly above the shower, not make standing in the shower a very cold experience on a winter's morning? :shock: That might work against your best efforts to drill the kids!

Would a separate humidistat detector and switch wired into the circuit solve the problem?

CliffordPope
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Re: Bathroom breathability

Post by CliffordPope » Fri 22nd Oct, 2021 8:29 am

worms wrote:
Fri 22nd Oct, 2021 7:54 am

Will drawing outside ambient air, directly above the shower, not make standing in the shower a very cold experience on a winter's morning?

It's not outside air, surely? I thought the point was it's warm but very humid air from inside being sucked out?

But yes, I've noticed showers can be pretty chilly merely from having a draught of any kind of air - the wind chilling effect.
I found it was vastly improved by fitting a cowl over the vent so that the air was drawn horizontally from round the ceiling, not in a direct line over one's shoulders.
I've often thought that the advice to mount the extractor grill close to the shower nozzle was mistaken.

worms
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Re: Bathroom breathability

Post by worms » Fri 22nd Oct, 2021 10:11 am

CliffordPope wrote:
Fri 22nd Oct, 2021 8:29 am
worms wrote:
Fri 22nd Oct, 2021 7:54 am

Will drawing outside ambient air, directly above the shower, not make standing in the shower a very cold experience on a winter's morning?

It's not outside air, surely? I thought the point was it's warm but very humid air from inside being sucked out?

But yes, I've noticed showers can be pretty chilly merely from having a draught of any kind of air - the wind chilling effect.
I found it was vastly improved by fitting a cowl over the vent so that the air was drawn horizontally from round the ceiling, not in a direct line over one's shoulders.
I've often thought that the advice to mount the extractor grill close to the shower nozzle was mistaken.
Ah yes! That would make more sense! Sorry, it was my interpretation of "drawing air in through a ceiling vent" that threw me off track! :oops:

Feltwell
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Re: Bathroom breathability

Post by Feltwell » Fri 22nd Oct, 2021 10:33 am

The idea if it's directly above the shower is the steam is carried away before it even gets a chance to land on a cold surface and condense. Drafts - yes, I have to convince Mrs F that the idea is not to have a shower then turn the fan on afterwards! Should be OK, the air is drawn in parallel with the ceiling rather than directly from below with the inlet I plan to use

worms
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Re: Bathroom breathability

Post by worms » Fri 22nd Oct, 2021 11:03 am

Our bathroom extractor fan is directly through one of the quarter-lights in the window (the ******* installer put it on the opening quarter, then screwed the window shut and removed the latches :roll: ). I've always intended moving it to a ceiling fan, but it would need to vent through the roof and I worry about condensation forming in the vent tube and either ponding or dripping back.

CliffordPope
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Re: Bathroom breathability

Post by CliffordPope » Fri 22nd Oct, 2021 12:06 pm

Feltwell wrote:
Fri 22nd Oct, 2021 10:33 am
The idea if it's directly above the shower is the steam is carried away before it even gets a chance to land on a cold surface ......... air is drawn in parallel with the ceiling rather than directly from below
Aren't those features contradictory? If the air is drawn in parallel with the ceiling then surely it does have a chance to condense there?

I don't think there is a perfect solution. If you have a fan there is bound to be some kind of draught.

Unless (sudden inspiration!) you had a hot air fan blowing air IN to the bathroom, and just a plain pipe somewhere near the ceiling to take the steam out. You could even have very hot air from a fan heater, and only turn it on for a few minutes AFTER showering, to dry everything out.

Feltwell
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Re: Bathroom breathability

Post by Feltwell » Fri 22nd Oct, 2021 1:54 pm

worms wrote:
Fri 22nd Oct, 2021 11:03 am
Our bathroom extractor fan is directly through one of the quarter-lights in the window (the ******* installer put it on the opening quarter, then screwed the window shut and removed the latches :roll: ). I've always intended moving it to a ceiling fan, but it would need to vent through the roof and I worry about condensation forming in the vent tube and either ponding or dripping back.
You put a fitting in the vent tube which catches the drips and puts them out through the soffit in a 22mm waste pipe - like this:-

https://www.amazon.co.uk/condensation-d ... B00BW329KI

Otherwise you'd definitely get it dripping back into the room!

As I've had to remove a wall here and fit a beam, I'm putting a new false ceiling in to hide the beam - the bathroom has a very high ceiling anyway so it won't look odd. That means my new inline fan can go above that ceiling (with a hatch for access) and vent out through the wall through the hole I'd already put in for the current, hopeless wall fan.
CliffordPope wrote:
Fri 22nd Oct, 2021 12:06 pm
Aren't those features contradictory? If the air is drawn in parallel with the ceiling then surely it does have a chance to condense there?
I don't think it'll be a great problem, the bulk of the moisture will just get sucked straight in - and the ceiling is warm so not so likely to suffer condensation as ceramic tiles on a external solid wall.

worms
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Re: Bathroom breathability

Post by worms » Fri 22nd Oct, 2021 5:16 pm

Feltwell wrote:
Fri 22nd Oct, 2021 1:54 pm
You put a fitting in the vent tube which catches the drips and puts them out through the soffit in a 22mm waste pipe - like this:-

https://www.amazon.co.uk/condensation-d ... B00BW329KI

Otherwise you'd definitely get it dripping back into the room!
Thanks, that looks useful...even though I don't have soffits!

worms
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Re: Bathroom breathability

Post by worms » Fri 22nd Oct, 2021 5:27 pm

CliffordPope wrote:
Fri 22nd Oct, 2021 12:06 pm
Unless (sudden inspiration!) you had a hot air fan blowing air IN to the bathroom, and just a plain pipe somewhere near the ceiling to take the steam out. You could even have very hot air from a fan heater, and only turn it on for a few minutes AFTER showering, to dry everything out.
You do get heat recovery bathroom extractor fans with a heat-exchanger to raise the temperature of the incoming cold air against the outgoing warm air.

I once had a house which came with an electric clothes drying cabinet. It was a bit like a shower cubicle which blew hot air in through side vents and had an extractor out the top. It worked really well, but was far too expensive in electricity to run it routinely. I always reckoned that having that system built in to the shower unit would be handy!

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