"Ian Stirling" wrote in message
...
IMM wrote:

"Ian Stirling" wrote in message
...
Rick Dipper wrote:

I have worked out the U values of the insulation I intend to use in
my
cavity walls, I have 2 solutions

1) Blocks -celotex-rockwall = 0.224 W/m2K
2) Blocks -2 * rockwall = 0.255 W/m2K

0.255 is poor. You should be aiming for 0.1ish

It kind of depends on the property.

0.1U would here (on all walls, floor and ceiling)
result in overheating most of the time except
in sub-zero temps from the ambient electrical load,
and human inhabitents, not to mention solar gain.

You install adequate ventilation.

If going from 0.25 to 0.1 costs around
1500 quid extra (and incidentally
knocks 50 cubic meters off the habitable
space), saving me no money,
unless it goes below 10C outside
(heating set to 20C now) and vanishingly
small amounts if it does. (currently I reckon
the overall insulation is
about 900W/K, with the walls having a U of about 2.4)

0.1ish is the point where a 2000 squ foot house does not require a full
heating system. So this extra £1500 is clawed back by not installing a full
heating system. As oil is not getting cheaper, it is a worthwhile investment
for the future. Also the insulation will keep out heat in the summer. All
makes sense.