"Andy Hall" wrote in message
...

If fuel rises, which it will as
cheap energy is coming to an end,
then this is meaningless and 450-500mm
is the optimum.

That's a separate issue. Can you suggest
a rate at which fuel prices would need to
rise to justify that?

Hold a finger to the air. Fuel prices will rise.
They always do. Also
enviro taxes will start to bite.

This is arm waving.

But arm waving with realism. All I read is that energy will become more
scarce and more expensive. As it becomes more exp[expensive so will
insulation too. best pack it in now while it is cheap enough. You will not
regret it in the future.

Yes we know all of that, but the figures are
not solid. Do you have energy price
projections for 5 and 10 years
time? You can make some guesses and
take a punt, but that is all it is.

See above.

In this instance, the cost of totally filling the roof with insulation
if you want is not significant so it doesn't matter.

My point was that focussing on this alone is misleading.

Who said focus on this alone?I never. I said pack in as much as you can
while it is cheap as it will not be, neither will energy, in the future.
probably sooner than later too.

Even if energy loss through the roof were reduced to zero by going to
the ridiculous lengths that you are suggesting,

I'm nor suggesting it. People who have done the research are.

Based on what?

See above.

In terms of return on investment, it may be interesting to do because
it is inexpensive, but then the returns are relatively little as well.

Loft insulation is cheap and very easy to do compared to other parts of
the
house. So it is worth packing in as much as possible.

I didn't dispute that it was cheap or
easy to do, but does result in
loss of space or extra timbers etc.
to make it usable.

That is still cheap and easy to do, even for a DIYer.

It doesn't make sense to make an
energy saving of 100W in the loft
when several kW are going out through the walls.

It does, as you can tackle the loft easily and cheaply. You plug as many
holes as you can, even the small ones.

My point was that focussing on this, while ignoring other much more
significant losses is the wrong focus. There is not much point in
saving £10 a year on what goes through the roof if £200 is going
through other surfaces. Even if energy goes up in price by a
factor of ten, that principle still applies. All that changes is the
urgency and the economics not the priority.

Ecohouse - A Design Guide says there is no upper limit to
insulation, as it will pay for itself eventually.

It's very easy to sit down and write airy-fairy books when it's other
people's money being spent. Almost anything pays for itself
*eventually* - that's a very weak argument.

In the book EcoHouse - A Design Guide, they gave a study that calculated
in
1987 200mm was the optimum in walls at the then current fuel prices.

Based on what?

"at the then current fuel prices"

As fuel prices rise and the insulation manufacturing costs too, the whole
payback calcs were skewed somewhat. So they calculated insulation levels
on
energy to make insulation. They came to the thickness of 650mm. The
conclusion was that what constrains you is the detailing of the structure
to
hold as much insulation as possible. So, install as much as possible.

Again based on what?

That is clear above.




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