150mm thick Knauff Space Blanket is on sale in B&Q at £3.74 for 1.97 sq
metres (to fit between joists at 40mm spacings). Roughly £1.90 per square
metre including VAT.
http://www.diy.com/diy/jsp/bq/nav.js...&isSearch=true

The R value is given as 3.4 and the U value as 0.044. No units.

Celotex GA3080 (80mm thick) is on sale from
http://www.just-insulation.com/celot...on_boards.html
at £8.06 per metre squared (+VAT).

The R value is given as 3.45 m.sq.K/W and the U value as 0.29 W/m.sq.K.

I have consulted Wikipedia at
http://en.wikipedia.org/wiki/R-value_%28insulation%29
to try and understand R and U values.

So:

(1) the R values look about right from the Wikipedia examples - and the
Celotex comes up as about twice as effective as the fibreglass per unit of
thickness.
(2) The fibreglass is about 1/5 the cost of Celotex for the same R value
(and this is from a discount Celotex web site).

So my one remaining problem is the U value.
If the U value is the reciprocal of the R value then for the same R value
shouldn't you have the same U value?
And if the R values are similar shouldn't the U values be similar?
Quick check with the calculator for 1/R shows that the Knauff figures are
wildly off. Should have an R value of about 22.7!

I have checked another site
http://www.space-insulation.com/blanket.html
and this gives the same figures for the 150mm space blanket, and includes
the units this time which are the standard SI units as shown for Celotex.

O.K. - dodgy (but consistent) figures from Knauff.

Strong cost justification for buying the space blanket which is no doubt
subsidised by me paying my heating bills.

Longer note than I intended - got baffled by U values part way through!

Cheers

Dave R

On Sat, 08 May 2010 14:49:12 +0100, Cicero
wrote:

Space blanket is probably much easier to install if it's going in a loft.
It will conform automatically to the joist spacings (requiring no
cutting) and it can have a second layer laid at right angles to the first
layer. It's also very clean to lay as it's fully encased. At the prices
you've seen (1:5) even two or three layers are more affordable than
Celotex.

The downside is that you virtually abandon your loft as a storage space.


I used Celotex under the boarded storage area and Knauf space blanket
for the rest. The best of both worlds, I think.

[Default] On Sat, 8 May 2010 13:16:27 +0100, a certain chimpanzee,
"David WE Roberts" , randomly hit the
keyboard and wrote:

(1) the R values look about right from the Wikipedia examples - and the
Celotex comes up as about twice as effective as the fibreglass per unit of
thickness.

Sounds about right.

So my one remaining problem is the U value.
If the U value is the reciprocal of the R value then for the same R value
shouldn't you have the same U value?

No because the U-value is the reciprocal of the SUM of the R-values.
In other words, you add the R-values of the inner and outer surface
resistances, the resistance of the plasterboard ceiling, the slates,
etc. And for added fun-filled jollity, you have to take cold bridging
by, for example, rafters and ceiling joists into account.

To compare the relative values of insulation, with everything else
being equal, it's safe to use the R-value as a guide.

Strong cost justification for buying the space blanket which is no doubt
subsidised by me paying my heating bills.

Where you have the space (in a large open loft space, for instance),
mineral fibre wins hands-down every time.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

On Mon, 10 May 2010 17:28:19 +0100, Hugo Nebula abuse@localhost
wrote:


Where you have the space (in a large open loft space, for instance),
mineral fibre wins hands-down every time.

Could this be used under a floor to insulate it from a 6ft deep void
underneath?

[Default] On Mon, 10 May 2010 20:37:21 +0100, a certain chimpanzee,
no-one , randomly hit the keyboard and wrote:

On Mon, 10 May 2010 17:28:19 +0100, Hugo Nebula abuse@localhost
wrote:


Where you have the space (in a large open loft space, for instance),
mineral fibre wins hands-down every time.

Could this be used under a floor to insulate it from a 6ft deep void
underneath?

Yep.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have I strayed"?

On Thu, 13 May 2010 20:34:07 +0100, Hugo Nebula abuse@localhost
wrote:

[Default] On Mon, 10 May 2010 20:37:21 +0100, a certain chimpanzee,
no-one , randomly hit the keyboard and wrote:

On Mon, 10 May 2010 17:28:19 +0100, Hugo Nebula abuse@localhost
wrote:


Where you have the space (in a large open loft space, for instance),
mineral fibre wins hands-down every time.

Could this be used under a floor to insulate it from a 6ft deep void
underneath?

Yep.

Thanks.