Mike Barnard wrote:
Hi.

I need a basic chart showing the heat losses through a loft area if
there is no insulation, 50mm, 100mm up to the 265mm nominal 'perfect'
insulation. Anyone know where there is one or the facts (validated)
so I can draw one up for myself?

Along the lines of...

One sq metre of uninsulated plasterboard has a U value of... ?

K value for plasterboard is 0.16. So U value of 16 for 10mm thick.. or
16 watts per square meter per degree centigrade.


Ditto with 50 mm standard rolled fibre insulation.

k value of glass fibre around 0.034 so a U value for 50mm is 20 times
that. 0.6 pr so? seems wrong..no..thats more or less right.

Ditto with 100 mm, 150 mm etc.


Divide by 2, 3 etc..


It's so I can show someone a comparison so she can decide just when
enough is enough compared with keeping spending more and more on more
materiels.


Note that when loose fiber insulation is used, the value of a WINDPROOF
layer like plasterboard is really high. Its not the same with celotex,
which is windproof to start with.

In terms of loft insulation around 100mm of rockwool, windproofed to the
hilt, is probably the best cost-benefit compromise.

If you want a useable surface there , fill between joists totally with
rockwool, then screw some 2x4s across the lot and fill again, then plate
over with chipboard.

If its to be left unused, then lay that last layer across the joists
instead.



I am googling, and it's ongoing, but all I find so far is detailed
tech guides or company ads. I'll bet someone on here has a link
already!

Thanks.