Fully enclosed shower cabinet against rough stone wall?

[meow2222]

Sucking lots of water laden air into that space sounds less than useful to me.

NT

[stuart noble]

It has the advantage of isolating your shower from the structure of the building

[mikehalmarack]

I can see how there would be something of a trade-off which might reduce the overall drying effect but it might be better than having areas of stagnant damp air behind the shower cubicle. At the end of the extraction run there would be more of a drying effect too.

[mikehalmarack]

That seems important to me under the circumstances.

[meow2222]

In winter, with a cavity the wall is going to be cooler than the room air. You spend 10 mins in the shower, passing warm saturated air over the cold w all, which will thus become much wetter. You then spend perhaps another 5 m inutes passing warm nearly saturated air over it, making it even wetter. Th is is not getting you where you want to go, quite the opposite.

NT

[meow2222]

I'm wondering what Stuart means by that

NT

[mikehalmarack]

OK, I'm convinced. :) So it would be better to have any extraction taking place elsewhere, perhaps with some kind of extraction ducting to the main extraction point taken from behind the shower cubicle. Then again, would this also introduce damp air into the void?

[stuart noble]

Only that the dampness could be a more wide ranging problem, and the OP may want a decent shower in the meantime.

[meow2222]

e:

r. You spend 10 mins in the shower, passing warm saturated air over the col d wall, which will thus become much wetter. You then spend perhaps another

5 minutes passing warm nearly saturated air over it, making it even wetter. This is not getting you where you want to go, quite the opposite.

I cant work out what you mean, its not clear. Nor why you'd run a duct to t he void.

NT

[meow2222]

It probably is. The op probably does. What did you mean by 'isolating your shower from the structure of the building' ?

NT

[newshound]

Not what I had in mind. When the shower fan is running, the cubicle is at a slightly lower pressure than the outside, and the fan is pulling warm damp air and discharging it outside. If you also have a few small holes in the top of the panel adjacent to the wall, air will also flow from that space into the shower cubicle and hence outside. Replacement air gets into the space either from under the floor (warm and dry) or the loft (cool and dry). In either case you should not be introducing particularly damp air to the space.

[mikehalmarack]

I was just having a Heath Robinson type brainstorm fantasy about placing the extractor elsewhere then running a duct from it to suck the air from the space between the shower cabinet and the wall. But life is already complicated enough.

[mikehalmarack]

[...]

Thanks for that explanation. I'm going to see if I can do this.

[mikehalmarack]

The conflict of opinion is not really surprising. I read numerous articles from both camps on the web. One claims rising damp doesn't exist, the other says squirt rubber and plastic all over the place to overcome it.

At least here, there were opinions expressed about my specific problem, although the exact same differences seem to have cropped up. Lots of good and helpful info though. I'm sure that by the time I've mulled it over a bit, I shall have moved on considerably toward a solution. Thanks all.

[meow2222]

With some of these questions you can get clear answers if you look in the r ight places. Look at BRE's research into rising damp, it seems pretty concl usive.

If you want to figure out the debate re damp & old buildings, the key is to understand a few core principles a) that the amount of water vapour air can hold is proportional to temperat ure, hence hot apparently dry air can hold more vapour than cold apparently damp air b) to understand that damp moves from inside to outside a building, not vic e versa, ie from warm air containing water vapour from breathing, showering , washing etc to lower temp and thus lower water vapour outdoor air c) the slow movement of water vapour outward through the walls is prone to result in interstitial condensation. A porous outer surface enables this to evaporate away harmlessly. Sealing the outside with nonporous paint causes water content to build up in the wall, which only worsens interstitial con densation. d) waterproof exterior paint prevents rain surface penetration, but also bl ocks ongoing evaporation. On balance it makes things damper, ie evaporation exceeds rain penetration.

I'd start with a building-wide assessment to see what causes there are of d ampness, and what can be remedied. There are typically several in damp old buildings. Bear in mind historic buildings normally can handle water vapour effectively by design, its usually later inappropriate treatment/maintenan ce/failure to maintain that result in problems building up.

NT

[stuart noble]

I think you're off your head

[mikehalmarack]

Thanks for the detailed explanation. I'll give it some thought and look at the sources you mention.

That may well be true of some designed buildings. this one started as a pile of stones with a roof over it in the 1600s. since then it's had a Hodges podgier of stone and brick additions, which may or may not have added to it's water vapour handling effectiveness.

[mikehalmarack]

If so, in the nicest and most informative way though.

[meow2222]

He offers no content whatever there, flatly refuses to go read up on this stuff, and resorts to personal abuse. Shrug.

NT

[meow2222]

e right places. Look at BRE's research into rising damp, it seems pretty co nclusive.

to understand a few core principles

rature, hence hot apparently dry air can hold more vapour than cold apparen tly damp air

vice versa, ie from warm air containing water vapour from breathing, shower ing, washing etc to lower temp and thus lower water vapour outdoor air

to result in interstitial condensation. A porous outer surface enables this to evaporate away harmlessly. Sealing the outside with nonporous paint cau ses water content to build up in the wall, which only worsens interstitial condensation.

blocks ongoing evaporation. On balance it makes things damper, ie evaporat ion exceeds rain penetration.

f dampness, and what can be remedied. There are typically several in damp o ld buildings. Bear in mind historic buildings normally can handle water vap our effectively by design, its usually later inappropriate treatment/mainte nance/failure to maintain that result in problems building up.

tively by design".

Its actually very simple for a masonry building to handle the British weath er, as long as its above ground and has the basics like guttering etc, and isn't in an issue producing situation such as being built against a rockfac e, being subject to frequent driving rain etc. The details of how buildings handle damp are however often misunderstood, and buildings often wrongly m aintained. On a modern house it doesnt much matter, the additional safeguar ds against damp make it very hard to screw things up. PPs dont have those e xtra safeguards, and things can go wrong. There's no shortage of people mak ing money selling inappropriate treatments and harbouring the usual misperc eptions like 'you need to keep the rain off the walls, I'll waterproof them for you for £500 with this overpriced gloop and all your problems will b e over.' If you think this unrealistic, start with some reading at SPAB.

NT