On Tue, 30 Dec 2003 09:06:21 +0000, {R} wrote:

In uk.d-i-y on Tue, 30 Dec 2003 03:05:20 +0000, Andy Hall
wrote:

}On Mon, 29 Dec 2003 19:23:37 +0000, {R} wrote:
[...]
}The new cupboard is very damp on the inside, soaking the wallpaper that
}was there before the cupboard. The cupboard is on the front wall of the
}SW facing house, 9" brick with a lathe and plaster finish.
}
}I think that you've done a good job, {R} but have made a very
}effective cold cupboard. It's possible that there is some
}penetrating damp through the brickwork, especially as the wall is SW
}facing, although the clue is that there was no apparent damp there
}before. Even so, I would do some obvious checks on the outside wall
}- for example is there a rainwater pipe that might be leaking, gutter
}overflowing, etc.? Could there be any crumbled brickwork? Worth a
}check.

Yes I have done that, I am convinced that it is not any form of leak. I
had one of those in the other corner of the room years ago and that was
fixed by reslating the roof. I failed to mention that the dampness is
very uniform over the whole of the inside of the outside wall.

OK, well there's your clue.


}However, if the cupboard is damp more or less uniformly across the
}back, then my money would be on condensation and lack of ventilation.
}The problem is that the heat loss through a solid 9" brick wall is
}quite substantial, so the action of building a cupboard has been
}effectively to reduce heat reaching this space from the room. It
}would be interesting to put a thermometer inside and see how much
}cooler it is than the room - I'd bet a good 10 degrees C. You don't
}say what you used to make the rest of the cupboard, but most of the
}composite sheet materials are pretty reasonable insulators, so in
}effect you are making a cool box next to the wall.

There isn't much of the rest of the cupboard, it is only 16" deep, being
built around the doors, and in a corner means there is only doors and
one end panel of thin pine T&G cladding.

So you will probably want to think about only 25mm Celotex to minimise
loss of depth.



}You say that not much in the house is original. Have you fitted
}double glazing and generally draughtproofed by any chance?

Oh yes.

There you go, you are setting up the conditions for condensation.


}If so, in the winter, you may have quite low ventilation in the house
}in general, leading to relatively high humidity. All that it then
}takes is a cold surface, and bingo. The air will certainly be
}finding its way into the cupboard, and my bet is condensing on the
}cold wall at the back.

Low ventilation? None is closer to the mark, I was extremely relieved
that when I had the gas boiler replaced after 22 years service the
installers insisted on better ventilation.

Certainly if it's a conventional flue model, this is essential. Not
having adequate ventilation will lead to CO production. Less
critical if it's a balanced flue - then the ventilation is typically
for the compartment in which it's installed.



SWMBO has a permanently cold hands and feet, and has ensured over the
years that there are no draughts at all. We even have a double entry cat
flap. I went and bought a CO monitor as I am/was concerned about the
ventilation. It is snug.

Had you thought about something like heat recovery ventilation? Vent
Axia make these among others. The idea is that you bring in and
exhaust air simultaneously through separate ducts but via the same
machine which sits in the loft, running continuously but at a very low
rate. The air leaving exchanges heat to the incoming, warming the
air. This way you get ventilation without creating draughts.


}Assuming you are satisfied that the outside wall is OK, then I think
}the next step would be to insulate the back of the cupboard. To do
}this, a good solution is polyisocyanurate foam, aka Celotex or
}Kingspan. This comes in 2440x1220mm sheets from builder's merchants
}in various thicknesses. 50mm is a very common one and readily
}available. This would take the heat loss through the wall almost
}down to modern house standards. Probably 25mm would be good enough
}to achieve the desired effect if you can get it. Expect to pay
}about £15 to £18 a sheet for it.

That is what I needed to know, thanks.

You're welcome.



{R}

..andy

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