On Thu, 22 Jan 2004 09:36:06 -0000, "IMM" wrote:


"Andy Hall" wrote in message
.. .


They talk about all sorts of things. This one is pure pandering to
be seen to be doing something towards the Kyoto protocol. It has no
basis in economics or anything else when put into the context of where
domestic energy should be being saved.

This is ********!

You're absolutely right. It is total ******** and political game
playing.

The Whole House Book has a graph that says 350-400mm is
the current optimum price/performance.

Based on what? Show the calculations. I wasn't talking about the
total environmental cost or anything of that nature, just very simple
economics of

a) what is the heat loss with insulation thickness X?
b) what is it with thickness Y?
c) what's the energy saving and what does that cost at today's prices?
d) what does it cost to install insulation to achieve that?

That is what the Whole House Book did.

Then please explain how it arrived at figures that justify these
figures, because it is not based on the parameters that I have
detailed.


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 fdiger to the air. Fuel porices will rise. They always do. Also
enviro taxes will start to bite.

This is arm waving. 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.

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.



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? If it includes all of the ecological factors involved
in manufacturing insulation as well then that is another discussion.
It can be a valid one for people for whom that is an important
concern, but it is separate nonetheless to the simple economic
argument.

if the walls and
window losses are not reduced then the difference made is worthless.

Keep in mind that the topic here was concerning the value *today* and
in the near future of increasing loft insulation.

Near future? What will that be? Ermmm...

Exactly. Who knows.


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.

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



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?



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?


There is also the comfort
factor of high insulation and that it also keeps the house cool from a
loft
hat may be 55C in summer.

Having any insulation will do that. It doesn't need to be knee deep
to achieve it.

The bigger the temp difference on each side and the bigger the heat
transfer. More insulation prevents heat transfer.

Yes. There is a simple equation covering this, and it is easy to
demonstrate that the major difference is between no insulation and
some rather than some and twice or three times as much.


..andy

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