On Mon, 16 Nov 2020 21:39:53 +0000 (GMT), Dave Liquorice wrote:

On Sun, 15 Nov 2020 23:03:41 +0000, alan_m wrote:

You can also get real wool insulation but more expensive ...

But very nice to handle and no irritating fibres or dust. It does
shed fibres though.

... and you need a thicker layer.

ICBA to do the research/maths but above 8 to 10 inches of these forms
of insulation you get into the releams of diminishing returns. We've
got 4" of real wool but under 22 mm chipboard which also has some
insulation value. An IR thermometer tells me the ceiling is the same
temp as the external internally insulated with 50mm celotex walls and
an IR camera showed the the same. Internal plasterboard walls are at
most 0.5C warmer...

Some heat is lost by convection causing percolation throgh the insulation;
the chipboard will stop this.
Since I boarded about 70% of the loft I'm very careful with vapour and use
the extractor in the bathroom for the obvious reasons and also for about 40
min. or so in the morning.
--
Peter.
The gods will stay away
whilst religions hold sway