You are looking at the house as a whole again. Duh! The extra
insulation
benefits greatly the upper rooms.

Of course I'm looking at the whole house. I pay the whole gas bill,
which covers the heating for the whole house. If I only paid for my
study, and my wife paid for the rest, then I'd turn the radiator off in
that room and buy a few jumpers.

The loft insulation is the depth over and above the 100mm.
That's right - the extra 300mm required to take it up to the 400mm you
requested. Well spotted.

You have to
take into account the fixing of the downstairs wall Kingspan.

I did, actually, because the costs I have been quoted for the Kingspan
alone are less than I mentioned, but I allowed extra for battening etc.

Loft
insulation is cheap and easy, so do it.
As I have shown, the loft insulation is the same cost and has a much
smaller benefit, so it is lower priority.

Also do downstairs too with
Kingspan, but the installation cost is greater.


Do you think I am made of money? If my budget is (lets say) £400, it's
either/or, not both. Insulating the downstairs wins hands down because
it has a much bigger effect for the same outlay.

Regards

Neil