On Fri, 7 Nov 2003 21:55:36 -0000, Peter Watson
wrote:



I take your point about the boarding preventing air circulation and
acting as insulation but how does this compare with more fibre? The
current suggested minimum is 200mm (and I note that some people have
gone upto 450mm - Surely there's a law of diminishing returns here!)
The suggested solution would only have 100mm insulation, and boards?

Thanks,

Peter


There certainly is a law of diminishing returns. If you look at the
U value of a roof with 100mm of insulation and work out the heat loss
for the area of a typical house it is generally a great deal less than
that which is lost through the walls and windows.

Doubling it to 200mm reduces that heat loss of course, but generally
to the tune of tens of watts. One can argue that the insulating
material is cheap enough so that the ROI on doing this is short but it
is rather like changing a 100W bulb for a 40W bulb while all the time
there is a 10kW heater running.

If the job can be done easily, then fine, but otherwise, if there is a
bunch of cost to install it such as timber etc. and that is not
otherwise useful, then going mad with roof insulation is not the most
cost effective way to deal with energy cost reduction.



..andy

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