Dry Lining and required gap

I am thing of dry lining a north facing bedroom in a flat which is suffering from condensation. Can you get vapour barrier polystrene backed plaster board which I could just grip fill to the wall or do I need a breathable air gap, or does the polystrene act as a vapour barrier on its own. Thanks
Steve Jones
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Almost - you can get vapour barrier Kingspan backed plasterboard which is twice as good.

Although the vapour barrier stops condensation from the occupants, there may still be some moisture ingress from outside (lots if you've got an old house) and so a small air gap and an airbrick near the floor will keep everything dry.
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So the air brick is behind the plaster board and vents the area behind the plaster board, doesn't go directly into the room? Do you require holes in the plaster boad to allow the free flow of air, if so does this not let condensation behind it. I was thinking of plasterboarding down to skirting board. Would gripfill allow enough of a air gap behind the plaster board ?
Thanks
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Yes. It's purely to remove moisture from the enclosed area. With no ventilation at all this area would gradually become damp and cause decay to any wooded joists above and below and possibly to the bricks.

so does

That's a different issue - the room needs ventilation to normal building regs practices but whether that is done through the plasterboard or windows is up to you. But I wouldn't allow any air from the room to reach behind the plasterboard.

Plaster adhesive is much cheaper - 6/25kg

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Small amounts of moisture will safely pass through the maisonary and evaporate to the outside as its no doubt currently doing on the uninsulated walls. The only probelms I can see would be if there is rising damp or if the outside is treated with something like a water proof render in which case I wouldnt bother at all especialy if its a cavity wall as there would be a risk of rusting the ties.
BaSiL

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wrote:

to
You can probably rely on this on south facing walls in protected areas but for a north facing wall exposed to heavy rain the overall averaged effect over the year will be water ingress, not egress.
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Is this just a theory of yours or can you point us to some resources to back it up?
I see a brick wall after heavy rain and it looks soaked, then a few hours latter it looks dry and not from evaporation to the inside. If the phenomonem you describe is correct wouldnt you see wall paper peeling off north facing externanal walls and salts appearing on crumbling plaster? and conversly that not happening on south facing walls? I havnt heard of that.
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wrote:

Sun and rain destroy pretty much anything over the years and, because our prevailing weather comes from south west, walls facing that way cop it far more than north or east facing.
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Stuart Noble wrote:

In my case, not so. I think my problem is wet walls freezing - on the north west side of the house in deep shade. This messes up the render and paint surface. Must put some sealer in those patches next summer and repaint..

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The pliolite products made by Johnstones and others are a *huge* improvement over water based masonry paint. I can't say for sure that it's totally cured my penetrating damp, but the signs are good. Can be applied in damp and cold conditions too, so no need to wait for summer :-)
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The walls are solid walls. I have noticed that in the bathroom the radiator is under the window and no damp. In all the other problem rooms radiators are on internal walls. Do you think it would help if the radiators where moved under the windows. Also if I add some room vents what height above floor should they be?
Thanks
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Is the bathroom upstairs and all the problem rooms downstairs ? More likely but obviously I don't know your house.

Million dollar question. I've had four sheets of Kingspan blocking a wall in a corridor all winter to identify the dampest parts. But my problem is probably a lot more harder to solve than yours (that part of house is 17xx). A foot from the floor is usually adequate.
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On 24 Feb 2005 03:48:59 -0800, snipped-for-privacy@scannex.co.uk (Stephen Jones) wrote:

Unless you have vissably damp walls I wouldnt waste any time on that, just attach the boards with plasterboard adhesive applied to the walls then after your join filler has dried paint drywall sealer as the vapour barrier. Thats what I did. I dont think the insulated boards are vapour sealed unless the maufacturer specificaly states it. Also drywall sealer gives a much nicer finish especialy on the joins than applying paint straight to the boards.
Bas
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Have you checked behind them ? I would bet that the damp is building up quite nicely in a puddle on the floor as that is exactly what I found when I removed poorly installed lining in my property.
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Quick check on my "poorly installed lining", no its dry as a bone!
The puddles you have seen sound exactly like you get with condensatiion. The vapour hits the dew point in within the insulation, condenses out and drips to the floor.
I used to get condensation on the North wall in the room I lined. But now obvously not now. So the wall is dryer for being lined.
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The walls are solid walls. I have noticed that in the bathroom the radiator is under the window and no damp. In all the other problem rooms radiators are on internal walls. Do you think it would help if the radiators where moved under the windows. Also if I add some room vents what height above floor should they be?
Thanks Post a follow-up
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Did you use standard plaster board or was it insulated, if insulated what thicknes and what was its trade name etc
Thanks for the advice
Steve
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On 28 Feb 2005 09:28:55 -0800, snipped-for-privacy@scannex.co.uk (Stephen Jones) wrote:

I used http://www.knaufdrywall.co.uk/themanual/frameset.html?http://www.knaufdrywall.co.uk/themanual/cgi-bin/special_flags.cgi?category_id=2
As much for sound insulation as anything. As there are better and cheaper laminate boards for thermal insulation I wouldnt recomend it unless you need sound insulation.
This looks good:
http://www.insulation.kingspan.com/newdiv/dry_lining.htm http://www.lafargeplasterboard.co.uk/products/prods/therm_res.htm
Without a vapour seal it will make your problems worse, and to make a neat job around the window frames and skirting and any coving etc will be demanding. If your ceilings are > 2.4m hight ( quite likely for you) the adhesive dabs method is more tricky.
I replied to your other thread too.
Basil
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