Reducing condensation problems

[a twig]

Simple things first, a proper centrifugal extractor fan.

Fitted one of the Manrose inline jobbies to our bathroom recently, and it has made a huge difference, no condensation on windows or walls anymore, even with a really hot shower running for ~15 minutes.

You can get a DewStop switch to control it which would suit your needs better than buying one with a built in humidistat.

 

[Penners]

Thanks a twig. What are the advantages of a centrifugal fan over an axial one? Is it simply efficiency?

I've had a look at the Dewstop humidistat online. It looks pretty much like any other humidistat - am I missing something? Or are you simply suggesting that a separate humidistat will work better than one built into the fan?

 

[Keithj]

For what it's worth: my daughter moved into a house with a large workshop behind the garage, in the same construction (4½ inch brick). She needed an office (she works from home) so we lined the lot with Jablite and then plasterboard over that. It was always damp and musty, and since she's asthmatic it wasn't much use.

Eventually, a "proper" builder was found, who traced the source of the damp (a stream running underneath, would you believe) and dealt with that. He removed the stuff we'd done, added air vents to the outside, Celotex and a membrane, an air gap, and plasterboard over that. Granddaughter 1 now has it as her "suite" and is delighted. There's no damp. The builder wouldn't say whether piping the stream, fitting vents, the air gap, the Celotex, the membrane, or a combination of them all fixed the problem. His comment was "belt and braces wins every time".

 

[a twig]

Dewstop was just an example for a separate humidity switch (other brands are available as the BBC like to say), the advantage of it as opposed to a built in is that you can fit it onto the walls you are trying to control the humidity of, and you can site it near the "worst case" places to ensure you are fully controlling it.

Centrifugal give a better pressure for a given volume, so are better at shifting the air down ductwork. Typically also you will see higher pumping speeds from a centrifugal, so the time the fan needs to run for will be lower as the damp air can be emptied quicker and shut the fan off again.

If you are just whacking the fan through an external wall to an outside vent then an axial would be fine, however I would vote for centrifugal as soon as any reasonable length of ductwork is involved.

I put one of these in the loft space above our bathroom, the difference has been amazing:
http://www.screwfix.com/p/manrose-mf100-w-100mm-mixed-flow-fan/26867

 

[Feltwell]

Did you use Tescon tape on the interior face of a butt joint between boards? Does it skim OK with plaster?

Is that the tape that overstates its profits then tries to stick itself desperately over the gaps and hopes that no one notices?

:lol: :lol: :lol:

Have you heard that Tesco are in even more trouble? The launch of their new Islamic range has angered the Muslim community - they claim the Prophets have been mis-represented.

 

[Penners]

:roll: :roll: :roll:

(That's the emoticon version of a loud groan!)

 

[Zebra]

Airtightness tape would probably be a bit over the top in your situation Penners if you can seal between the insulated plasterboards effectively with silicone or whatever. I've used it where there will be movement: between the OSB airtightness layer and the 17th C timber frame.

 

[Flyfisher]

Would it be a fairly simple job to installed a suitable extractor fan first and see what happens? Sounds like less work (and cost) that a complete lining/insulation job, and wouldn't preclude that later should extraction alone not be sufficient.

Yes, that would certainly be the simplest/quickest solution, FF. I suppose I'm just a bit sceptical about whether it would be sufficiently effective without some kind of further condensation prevention on the walls. As I mentioned above, I have noticed that the black mould is forming particularly in the corners of the room and behind bits of furniture, from which I assume that the air in those locations is not being moved sufficiently for it to pass through the dehumidifier. So I wonder whether a humidistat-controlled extractor would have any better success.

But I take your point that further work could be done later if the humidistat fan failed to provide a complete solution.

Dilemma, dilemma....!

That's an interesting observation, so how about trying something even simpler and totally non-invasive . . . a fan? Some sort of oscillating pedestal fan could perhaps ensure the air within the room is properly circulated and thoroughly mixed, giving the dehumidifier a chance to work with ALL the air in the room. It would also be a more energy efficient solution as warm air would not be extracted and therefore wasted. I've no idea if it would work, but it would be simple to try with no impact to the room itself.

 

[Penners]

That's a great idea, FF. However far down the insulate/dehumidify/extract route I finally decide to go, I'll definitely try that as a supplementary approach. I already have a suitable fan, so zero additional cost (apart from a small amount of 'lectric!).

Many thanks.

 

[jackpoint]

It's a tricky thing. We're looking at some sort of insulation on the nine inch walls while the house is in bits and it boggles the brain!
All I can offer to the discussion is this piece from the celotex website....
http://www.celotex.co.uk/applications/wall-insulation/internal-solid-walls

Ideal where no cavity exists, the Celotex internally insulated solid masonry wall solution is suitable for both direct bonding (‘dot and dab’) and mechanical fixing installation. This application provides a vapor control layer (VCL) when board joints are tapered and jointed, and is particularly suited to refurbishment projects.

I think there is a more detailed pdf there too.

We are currently thinking airbrick vented small cavity, membrane, 40-50mm layer of celotex to reduce thermal bridging, then something like a 50mm stud type wall to run the services in with more celotex stuffing. Probably not as complicated to do as it sounds

 

[Lime]

As a matter of interest one of our bedrooms gets very cold (north facing) and used to suffer black mould behind furnishings etc. even though a window was open most of the time.
I cured the problem by installing a oscillating desk fan on the floor to circulate the air.
It is on a time switch and uses night-time cheap rate electricity.
The problem of condensation has gone away but I wouldn't wish to be in the room for very long with the fan on because of the draught it causes.

 

[Penners]

where no cavity exists, the Celotex internally insulated solid masonry wall solution is suitable for both direct bonding (‘dot and dab’) and mechanical fixing installation. This application provides a vapor control layer (VCL) when board joints are tapered and jointed, and is particularly suited to refurbishment projects.

Thanks for your comments, jackpoint. Rather than the dot and dab fixing method, I'm mor ein favour of a continuous bead of silicone around the perimeter of each board, supplemented by a grid of "dots". This will tend to exclude warm, moist air from the small gap left between the insulation and the brick wall.

 

[TheRoost]

Isn't fitting an extractor fan a bit over the top for a room that isn't creating warm damp air like a kitchen or bathroom would? A standard extractor can make a room very cold from draughts(especially when windy) so you would have to use your heating more. Insulating the walls doesn't have this drawback.

Do the windows have a ventilation setting, or could you install adjustable window vents, it might be all that's needed to give enough air changes to prevent condensation/mould forming.

Is your dehumidifier a compressor type? does it extract much moisture, is the room warm enough overnight for it to work properly?

 

[Penners]

It's a very small room, TheRoost, so just Mrs P's breath is enough to cause condensation (please notice that I avoided mentioning how much of the time her mouth is open!). Your comment about draughts is a valid one, but I'm aware that the best formula for getting rid of condensation is warmth and ventilation. The window is quite elderly (ie: probably 30 years old) so it has no trickle vents.

The dehumidifier is the type (can't remember the name - wick?) that will work at low temperatures.

 

[Keith Bowman]

All sounds far too modern. Punkah wallah. That's what you need. And the punkah for the punkah wallah to wallah.

 

[Penners]

Ah - shades of It Ain't 'Arf Hot Mum and Carry On Up The Khyber! Could the punkah wallah be called Bungdit Din? Could I be The Khasi of Kalabar?

 

[formerly known as]

lime plaster and limewash is a good way of combating condensation without setting up mechanism's for interstitial condensation.