Hugo Nebula wrote:

On 18 Jun 2004 20:52:59 +0100, a particular chimpanzee named John
Richer randomly hit the keyboard and produced:


Thanks - the relative performance was just what I was looking for.


The conductivity ('k-value' or 'lambda-value') is the relative
performance. AFAIR, the k-value for mineral wool is 0.037W/m^2K,
whereas for Celotex it's 0.023W/m^2K


So this suggests that if I do get to 50mm celotex, then I have done
enough. The attic rooms have sloping ceilings with loose fill
insulation poured between slates and lath-and-plaster sloping walls (a
previous owner's contribution to the house) so they will dominate the
heat flow.


I think I suggested at least 100mm thick Celotex. Although something
is better than nothing.

Your previous owner's contribution appears to be to create a high risk
of condensation in your roof by blocking the ventilation path between
the insulation and the roof felt.

Agreed. You should try and put the celotex down the sloping bits, with
an air gap above.

Probaly means ripping out all the ceilings tho.