On Thu, 22 Jan 2004 00:59:39 -0000, "IMM" wrote:

"Andy Hall" wrote in message
.. .
On Thu, 22 Jan 2004 00:02:57 -0000, "G&M" wrote:

"Christian McArdle" wrote in message
. net...
Is there a noticable difference in loft insulation (rockwool rolls)
in
insulating greater than a 4" depth?

Yes. The law of diminishing returns says that 350mm is the best
environmentally speaking. Any more and the environmental cost of
manufacturing and transporting the insulant is higher than the energy
saved.
100mm is definitely on the low side. 200mm would be better. The
difference
between 200mm and 350mm isn't that great.

Are you sure on this. It's just I heard the ODPM people who set the
building regs were talking about as much as 450mm in the next part L.

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?

Based on the hard figures and those assumptions *only* please explain
where you feel that there is a mistake in the numbers.


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?

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

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.

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. Do the sums. The temperature differences put the
heat gain in the low hundreds of watts over an entire house even with
just 100mm of glass fibre. On a room by room basis, not much more
than a light bulb.

If people in government and elsewhere want to advocate that homeowners
should put more insulation in their roofs, that's fine - as you say
it's cheap and easy. However the *complete* picture, including the
economics and the comparisons with other energy saving should be
presented and it is not. The reality is that the government wants
to demonstrate in the international conference scene that it is doing
something with respect to Kyoto. There is nothing wrong with the
sentiment of that, but it should be done on an honest basis, and this
is not.






---

..andy

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