In article ,
Roger Chapman writes:
On 27/02/2011 18:41, Andrew Gabriel wrote:

snip

The house has temperature logging, but not in the loft. So, I just
added a sensor in the loft and I'll compare it with the outside sensor.
Having come out of the loft and closed the hatch, the loft temperature
is rapidly dropping towards outside temperature, but too early to know
where it will settle yet.

Temperature is only half the equation. Do you have a dehumidifer to put
up there for a bit to see how much water you can extract at say 80%
humidity?

I do have one, but they don't work at the current loft temp (6C) as
the evaporator ices up. I could perhaps put it upstairs with the
outlet ducted up into the loft as a measure to dry it out quickly.

I have some readings now. Last night and this morning, loft stays
2C higher than outside temperature. It's been continuously cloudly
over that period, so no radiative cooling or heating to speak of,
and no wind to speak of.

I varied upstairs temperature from 16.5C to 20.5C over night and it
made no difference to loft temperature, but this would probably need
running over a longer period to get a noticable effect.

This morning, I put 500W of heating in the loft to see what impact
that has on the temperature. That raises the loft by a further
4C, to 6C above outside. Very conveniently, the outside temperature
hasn't changed over this period, so the temperature rise should be
proportional to the heat loss, so that implies that I'm normally
losing about 250W through the new loft insulation. I don't have
equivalent measurements before doing the extra insulation, but I
would imagine it could well be many times that heat loss.

Another interesting observation. In the loft is a large metal tray,
4' x 3' (originally the side from a 19" rack). It was originally
supported above the new insulation, but the insulation has expanded
a bit since laying, and was now touching the bottom. There is a
little condensation on the bottom of this, which implies some
moisture is working it's way through the ceiling, which is lath
and plaster at that point, but not cracked. I still find it hard
to believe all the moisture in the loft is coming from the house
though.

--
Andrew Gabriel
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