I have a new 20'x7' shed which my wife will use as an artist's studio.
The shed is heavy duty T+G. I want to insulate the walls and roof.

My local Sheffield Insulation trade Counter recommends new-fangled
stuff called "Frame Foil" stapled onto the uprights of the shed walls,
with "moisture board" directly on top of that. But it will be pricy -
I reckon about £600 for the Frame Foil alone.

1. How good is "Frame Foil"?

2. What alternatives are there? Preferably cheaper...

3. Could I use T+G pine cladding?

4. What gaps do I need between "moisture board", insulation and
outside walls?

5. There will be a 5-socket ring in the shed. What is the best way to
get the connections to the electricity sockets through any wall
covering/plastic membrane/insulation?

Many thanks to all

On 2008-07-24 13:15:07 +0100, JP Coetzee said:


I have a new 20'x7' shed which my wife will use as an artist's studio.
The shed is heavy duty T+G. I want to insulate the walls and roof.

My local Sheffield Insulation trade Counter recommends new-fangled
stuff called "Frame Foil" stapled onto the uprights of the shed walls,
with "moisture board" directly on top of that. But it will be pricy -
I reckon about £600 for the Frame Foil alone.

1. How good is "Frame Foil"?

2. What alternatives are there? Preferably cheaper...


This seems unnecessarily complicated.

Have a look at Celotex and Kingspan. This is polyisocyanurate foam
with foil front and back as a vapour barrier. 50mm would be fine for
this application or thicker if you don't mind losing some space.



3. Could I use T+G pine cladding?

Yes




4. What gaps do I need between "moisture board", insulation and
outside walls?

I did a similar project for a cabin. I put vertical studs of
pressure treated timber fitted to the outside walls and 75mm deep. The
whole inside was then sprayed with Cuprinol clear wood preservative -
the solvent based proper one as opposed to the watery girls version.

The Celotex sheet was sandwiched in between and taped using the special
foil tape, thus leaving a space of about 25mm between the backside of
the sheet and the outside wall for ventilation. The same thing was
done for the pitched roof. I had already done the floor by laying in
Celotex on spacers before butting down the floor boards.

I then used a 9mm T&G cladding secret nailed to the studs (hint an air
nailer is good here) and finally used a clear acrylic matt varnish
(watery girls one).




5. There will be a 5-socket ring in the shed. What is the best way to
get the connections to the electricity sockets through any wall
covering/plastic membrane/insulation?

I put in 20mm plastic conduit throughout for hidden sockets and ran PVC
single conductors inside.

I then ran three compartment trunking around the whole thing. This
allows for easy modification.




Many thanks to all

On 24 Jul, 13:15, JP Coetzee wrote:
I have a new 20'x7' shed which my wife will use as an artist's studio.
The shed is heavy duty T+G. I want to insulate the walls and roof.

My local Sheffield Insulation trade Counter recommends new-fangled
stuff called "Frame Foil" stapled onto the uprights of the shed walls,

It's all surprisingly expensive. You need to learn what R,K & U values
are about, then run the numbers (simple spreadsheet) to make any sense
at all. Watch out, as most things are listed (on the web anyway) in US
units for R value. Also look at finished costs, including battens,
membranes and plasterboard.

K is an inherent property of the material. R is the overall
performance of a wall component (one material layer), taking into
account its thickness. You can get total wall performance by adding up
the R for each layer (Big R is good). To a rough approximation, R for
bulk materials (glasswool) is their thickness divided by their K. U
is the reciprocal of R and you might see building standards for
finished wall expressed in it (little U is good).

If you use SI units, that's it. If you use US units, there are screwy
conversion factors everywhere.

For a material like Frame Foil or plasterboard that only comes in
"finished thickness", then there's no K value, just one overall R.

Frame foil is deliberately designed to have an R value about the same
as 150mm glasswool, a "typical" insulation level for walls.

What's good about it?

* Thin. It's about 65mm thick overall - inch for the foil layer, 3/4"
airgap either side. You _must_ preserve this airgap!

* Built in vapour membrane.

* Easy to install. Not so much bulk to worry about.

* Resistant to cold bridging. You can squash it narrow without loosing
too much performance and you can squash it entirely flat and still
have a little. Compare this to glasswool against a stud where it tips
away a little and leaves a gaping gap.

* Easy to install, especially on walls.

What's bad?

* Performance isn't quite as good as a really thick glasswool layer.

* Easy to screw up the installation. Squashing it or not providing the
airgap (use counterbattens before plasterboarding over it!) will
produce a poorly performing wall.

* Easily confused with "bubble" foils that only have about half of the
R performance.

* Bad reputation with some regulatory bodies, owing to inept testing
methods a few years ago. Lots of people will tell you "it doesn't
work".

* Cost.


About the best (practical) insulation / thickness performance is from
Cellotex etc. yellow foam rigid boards with isocyanate foam and silver
foil faces. These are 65mm too, about the same as Frame Foil.

Cheapest (and perfectly good) is rockwool or glasswool of 150mm or so.
Somewhat more labour to fit and it's two or three times thicker, which
can be an issue for headroom in some retrofit locations.

Your price appears to be roughly £10/m^2, which is slightly more than
glasswool (by the time you've put plasterboard over it). Yellow foam
is more than this, maybe £15-20 / m^2 and the bubble stuff is half
this, maybe £5/m^2.

I use the foil on walls, because the ease of installation is useful.
If I don't care about thickness, I'd go with glasswool. For retrofit
insulation I'd look at the yellow foams, which I don't otherwise like
owing to price and chemistry.

On 24 Jul, 13:15, JP Coetzee wrote:

This is a cute demo calculator that's worth a play with:
http://www.ybsinsulation.com/timberf...lculations.htm

Thanks for the advice so far. A little more background:

* The shed is already installed. It backs up against a rough stone
wall i.e. I can't get behind it.

* The internal wall battens are about 44mm thick, the roof battens
about 66mm. I won't build out thicker than that or the shed will
become too claustrophobic. What is the best insulation I can provide
in those depths? I realise the shed will need heating in the depths of
winter.

BTW the Frame Foil expert at Sheffield Insulation said it would be
fine to put plasterboard directly on top of the foil i.e. no air gap
on the internal side. Would you disagree?

Thanks for your advice so far. A little more background:

* The shed is already installed. It backs up against a rough stone
wall i.e. I can't get behind it.

* The internal wall battens are about 44mm thick, the roof battens are
about 66mm. I won't build out thicker than that or the shed will
become too claustrophobic. What insulation can I use in those depths?

BTW the Frame Foil expert at Sheffield Insulation said it would be
fine to put plasterboard directly on top of the foil i.e. no air gap
on the internal side. Would you disagree?

JP Coetzee wrote:
Thanks for the advice so far. A little more background:

* The shed is already installed. It backs up against a rough stone
wall i.e. I can't get behind it.

* The internal wall battens are about 44mm thick, the roof battens
about 66mm. I won't build out thicker than that or the shed will
become too claustrophobic. What is the best insulation I can provide
in those depths? I realise the shed will need heating in the depths of
winter.

BTW the Frame Foil expert at Sheffield Insulation said it would be
fine to put plasterboard directly on top of the foil i.e. no air gap
on the internal side. Would you disagree?

Certainly goes against what the Frame Foil installation instructions
explicitly state. (Interest made me check it out earlier.)

http://www.solentinsulation.co.uk/productsection/Framefoil%20Brochure%2030%20May.pdf

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

On 24 Jul, 20:27, JP Coetzee wrote:
Thanks for your advice so far. A little more background:

* The shed is already installed. It backs up against a rough stone
wall i.e. I can't get behind it.

No problem. Either foil, yellow foam or even (with a struggle)
rockwool can retrofit from the inside alone.

* The internal wall battens are about 44mm thick, the roof battens are
about 66mm. I won't build out thicker than that or the shed will
become too claustrophobic. What insulation can I use in those depths?

If you're that tight for space, then by all means go with the foil.

I'd suggest attaching a "sub-batten" alongside the wall battens and
stapling the foil down to those. You can get away without the full
airgap, but you do need _some_ reliable airgap. If you have contact on
the sides of the foil, then its insulation ability drops radically.

BTW the Frame Foil expert at Sheffield Insulation said it would be
fine to put plasterboard directly on top of the foil i.e. no air gap
on the internal side. Would you disagree?

Yes. Of course you _can_ do this, but if you put pressure on the foil
then it presses flat and turns into a cheap vapour barrier and no
more. So don't do that.

On 2008-07-24 20:25:59 +0100, JP Coetzee said:

Thanks for the advice so far. A little more background:

* The shed is already installed. It backs up against a rough stone
wall i.e. I can't get behind it.

Not a problem


* The internal wall battens are about 44mm thick, the roof battens
about 66mm. I won't build out thicker than that or the shed will
become too claustrophobic. What is the best insulation I can provide
in those depths? I realise the shed will need heating in the depths of
winter.

You could use 35mm Celotex for the walls and 50mm for the roof. As
long as there is some ventilation at the back on the cold side you will
be OK.




BTW the Frame Foil expert at Sheffield Insulation said it would be
fine to put plasterboard directly on top of the foil i.e. no air gap
on the internal side. Would you disagree?

On the internal side, that's fine.

On Jul 24, 8:49*pm, Andy Dingley wrote:
I'd suggest attaching a "sub-batten" alongside the wall battens and
stapling the foil down to those.

How about if I stapled the foil half-way down the batten instead i.e.
the staples are o



So instead of:

-------------------------------------- Foil
##############
##############
##############
### ###
### Batten ###
### ###
##############
###################################### Wood


I do:

+----------------+ Foil
| ############## |
| ############## |
| ############## |
--------+ ### ### +-----------
### Batten ###
### ###
##############
###################################### Wood

The foil would be pulling at right angles to the staples. Is it likely
to tear?

On Jul 24, 8:49 pm, Andy Dingley wrote:
I'd suggest attaching a "sub-batten" alongside the wall battens and
stapling the foil down to those.

How about if I staple the foil "half-way down" the thickness of the
batten, i.e.:

Instead of:

-------------------------------------- Foil
##############
##############
##############
### ###
### Batten ###
### ###
##############
###################################### Wood


I do:

+----------------+ Foil
| ############## |
| ############## |
| ############## |
--------+ ### ### +-----------
### Batten ###
### ###
##############
###################################### Wood

The foil would be pulling at right angles to the staples. Is it likely
to tear?

(That diagram might look funny in a newsreader)

On 2008-07-25 08:52:09 +0100, JP Coetzee said:

On Jul 24, 8:49 pm, Andy Dingley wrote:
I'd suggest attaching a "sub-batten" alongside the wall battens and
stapling the foil down to those.

How about if I staple the foil "half-way down" the thickness of the
batten, i.e.:

Instead of:

-------------------------------------- Foil
##############
##############
##############
### ###
### Batten ###
### ###
##############
###################################### Wood


I do:

+----------------+ Foil
| ############## |
| ############## |
| ############## |
--------+ ### ### +-----------
### Batten ###
### ###
##############
###################################### Wood

The foil would be pulling at right angles to the staples. Is it likely
to tear?

(That diagram might look funny in a newsreader)

I think you would have difficulty in sealing the edges by doing it this way.

On 25 Jul, 08:52, JP Coetzee wrote:
On Jul 24, 8:49 pm, Andy Dingley wrote:

I'd suggest attaching a "sub-batten" alongside the wall battens and
stapling the foil down to those.

How about if I staple the foil "half-way down" the thickness of the
batten, i.e.:

If you can do it without putting excess tension of the foil _and_
without leaving the foil loose enough that it can flap around and rest
on one of the inner surfaces .

On Jul 25, 8:52*am, JP Coetzee wrote:
On Jul 24, 8:49 pm, Andy Dingley wrote:

I'd suggest attaching a "sub-batten" alongside the wall battens and
stapling the foil down to those.

How about if I staple the foil "half-way down" the thickness of the
batten, i.e.:

Instead of:

-------------------------------------- Foil
* * * * * ##############
* * * * * ##############
* * * * * ##############
* * * * * ### * * * *###
* * * * * ### Batten ###
* * * * * ### * * * *###
* * * * * ##############
###################################### Wood

I do:

* * * * +----------------+ * * * * * * Foil
* * * * | ############## |
* * * * | ############## |
* * * * | ############## |
--------+ ### * * * *### +-----------
* * * * * ### Batten ###
* * * * * ### * * * *###
* * * * * ##############
###################################### Wood

The foil would be pulling at right angles to the staples. Is it likely
to tear?

(That diagram might look funny in a newsreader)

You may be better off using a thin strip of 6mm ply and stapling
through that to the side of the stud.

cheers,
Pete.

cheers,
Pete.

On Thu, 24 Jul 2008 10:51:28 -0700 (PDT), a particular chimpanzee,
Andy Dingley randomly hit the keyboard and
produced:

On 24 Jul, 13:15, JP Coetzee wrote:

This is a cute demo calculator that's worth a play with:
http://www.ybsinsulation.com/timberf...lculations.htm

Yes, but don't believe a word of it, though.

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials. Some manufacturers
have had it tested properly, and use resistance figures of ~1.7m²K/W;
YBS I notice still quote the very discredited 6.1m²K/W. Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

On 2008-07-25 20:44:57 +0100, Hugo Nebula abuse@localhost said:

On Thu, 24 Jul 2008 10:51:28 -0700 (PDT), a particular chimpanzee,
Andy Dingley randomly hit the keyboard and
produced:

On 24 Jul, 13:15, JP Coetzee wrote:

This is a cute demo calculator that's worth a play with:
http://www.ybsinsulation.com/timberf...lculations.htm

Yes, but don't believe a word of it, though.

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials. Some manufacturers
have had it tested properly, and use resistance figures of ~1.7m²K/W;
YBS I notice still quote the very discredited 6.1m²K/W. Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.

So no better than a rather thin sheet of Celotex?

On Fri, 25 Jul 2008 20:44:57 +0100, Hugo Nebula abuse@localhost wrote:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials. Some manufacturers
have had it tested properly,

"properly" is arguable here.

Hugo Nebula wrote:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials. Some manufacturers
have had it tested properly, and use resistance figures of ~1.7m²K/W;
YBS I notice still quote the very discredited 6.1m²K/W. Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.

"For a successful technology, reality must take precedence over public
relations, for nature cannot be fooled." [Richard Feynman]

--
Andy

On Fri, 25 Jul 2008 23:35:49 +0100, a particular chimpanzee, Andy
Dingley randomly hit the keyboard and
produced:

On Fri, 25 Jul 2008 20:44:57 +0100, Hugo Nebula abuse@localhost wrote:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials. Some manufacturers
have had it tested properly,

"properly" is arguable here.

Actually, they have. One manufacturer (Thinsulex, IIRC) has a BBA
certificate for their product.

You may be thinking of the discredited TRADA test. TRADA, who are UKAS
accredited but not for insulation, certified Tri-Iso Super 9 as having
the equivalent R-value as 200mm of Rockwool. Many in Building Control
questioned the methodology of the test[*], but no-one seemed to have
spotted that their certificate wasn't worth the paper it was emailed
on.
[*] This involved two small 'rabbit hutches' in the south of France,
one insulated with 200mm Rockwool, the other with Tri-Iso. The test
reports said that both used similar amounts of energy to maintain the
internal temperature, which therefore proved that Tri-Iso was the
equivalent of 200mm Rockwool. What the report didn't say, and what
TRADA refused to say when asked, was what the amount of energy used
was. In other words, both 'hutches' could have been unheated.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

On Fri, 25 Jul 2008 20:55:16 +0100, a particular chimpanzee, Andy Hall
randomly hit the keyboard and produced:

On 2008-07-25 20:44:57 +0100, Hugo Nebula abuse@localhost said:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials....Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.

So no better than a rather thin sheet of Celotex?

Equivalent to a 40mm sheet, yes. Which means that, when installed
properly with a 25mm airgap either side, it is thicker than PIR
insulation.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

On 2008-07-26 09:39:16 +0100, Andy Wade said:

Hugo Nebula wrote:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials. Some manufacturers
have had it tested properly, and use resistance figures of ~1.7m²K/W;
YBS I notice still quote the very discredited 6.1m²K/W. Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.

"For a successful technology, reality must take precedence over public
relations, for nature cannot be fooled." [Richard Feynman]

I like that one.

On 2008-07-26 09:49:45 +0100, Hugo Nebula abuse@localhost said:

On Fri, 25 Jul 2008 20:55:16 +0100, a particular chimpanzee, Andy Hall
randomly hit the keyboard and produced:

On 2008-07-25 20:44:57 +0100, Hugo Nebula abuse@localhost said:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials....Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.

So no better than a rather thin sheet of Celotex?

Equivalent to a 40mm sheet, yes. Which means that, when installed
properly with a 25mm airgap either side, it is thicker than PIR
insulation.

Well OK. For this project, (i.e. not a controlled development),
40-50mm Celotex would be fine and it isn't really necessary for there
to be an air gap at the front. Plus I believe that the foam is less
expensive. It is certainly easier to fit and seal.

"Hugo Nebula" abuse@localhost wrote in message
...
On Fri, 25 Jul 2008 20:55:16 +0100, a particular chimpanzee, Andy Hall
randomly hit the keyboard and produced:

On 2008-07-25 20:44:57 +0100, Hugo Nebula abuse@localhost said:

Multi-foils have been caught out in recent years lying through their
teeth about the performance of their materials....Real world
testing has been done proving that anything more than 1.7m²K/W is
bull****.

So no better than a rather thin sheet of Celotex?

Equivalent to a 40mm sheet, yes. Which means that, when installed
properly with a 25mm airgap either side, it is thicker than PIR
insulation.

A piece of cling film with a 25 mm air gap either side would be as good.
Its the air supplying the insulation not the foil.

On 26 Jul, 20:12, "dennis@home" wrote:

A piece of cling film with a 25 mm air gap either side would be as good.
Its the air supplying the insulation not the foil.

You haven't seen the insulating foils, have you?

They're not a single layer, they're a quilted blanket that contains
_multiple_ airgaps. That's why they have better performance than a
single layer of clingfilm.

"Andy Dingley" wrote in message
...
On 26 Jul, 20:12, "dennis@home" wrote:

A piece of cling film with a 25 mm air gap either side would be as good.
Its the air supplying the insulation not the foil.

You haven't seen the insulating foils, have you?

They're not a single layer, they're a quilted blanket that contains
_multiple_ airgaps. That's why they have better performance than a
single layer of clingfilm.

Only if they trap a significant amount of air, the ones I have seen don't!

There is no way they acheive the claimed insulation figures.. it isn't
possible.

If you want to argue then use two layers of cling film with a 20 mm gap and
beat the foil with ease.

On 28 Jul, 12:09, "dennis@home" wrote:

They're not a single layer, they're a quilted blanket that contains
_multiple_ airgaps. That's why they have better performance than a
single layer of clingfilm.

Only if they trap a significant amount of air, the ones I have seen don't!

They trap an _insignificant_ amount of air, that's their virtue
(Assuming that "significant" is taken to mean "larger" than
"insignificant", for the purpose of our discussions here).

Because they only trap small individual volumes, the temperature
differences across the volume is too low (relative to the space) to
set up an efficient convection cell. This is why they're more
efficient that clingfilm (and a large convective cell) and why they
need multiple layers (to reduce temperature differences across each
cell).

"Andy Dingley" wrote in message
...
On 28 Jul, 12:09, "dennis@home" wrote:

They're not a single layer, they're a quilted blanket that contains
_multiple_ airgaps. That's why they have better performance than a
single layer of clingfilm.

Only if they trap a significant amount of air, the ones I have seen
don't!

They trap an _insignificant_ amount of air, that's their virtue
(Assuming that "significant" is taken to mean "larger" than
"insignificant", for the purpose of our discussions here).

So there is no air to provide insulation then?
I will give you a hint.. it isn't the mineral wool in mineral wool that
insulates, it isn't the cellulose in cellulose fibre that insulates it isn't
the plastic in polyurethane foam that insulates and as you say there is an
insignificant amount of air in foil insulations.


Because they only trap small individual volumes, the temperature
differences across the volume is too low (relative to the space) to
set up an efficient convection cell. This is why they're more
efficient that clingfilm (and a large convective cell) and why they
need multiple layers (to reduce temperature differences across each
cell).

You get a static layer of air about 6 mm deep on any surface.
You don't need to create cells to make it work.
Cling film will have about 6 mm of static insulating air on each side just
like double glazing does.
Foils aren't thick enough to have this 6 mm layer of air so they conduct
more heat.
You have a basic problem with your physics ATM.

On 28 Jul, 15:05, "dennis@home" wrote:

You have a basic problem with your physics ATM.

Dennis, you're the guy who thinks that hot lightbulbs cause
condensation.

On 28 Jul, 15:05, "dennis@home" wrote:

So there is no air to provide insulation then?

Air doesn't insulate, it transfers the heat. It's a worse transfer
medium than typical solids, so in the sense of that comparison it's an
"insulator", but it's still worse than a vacuum. In particular,
circulating air is a fairly large means of heat transfer. So to apply
the idea of "a blanket of air is an insulator", then this must be a
blanket of _still_, stagnant air, not just any old thickness of
unconstrained air.

A thicker layer of wood or plasterboard is a better insulator. A
thicker layer of air, particularly on a small scale, is a _worse_
insulator.

If you have a thick layer of air with a heat differential across it,
you'll get a convection current starting. If you can make the layer of
air thinner, still at the same temperature gradient (i.e. slicing it
up with multi-foils) then convection becomes less efficient and the
overall insulation goes up. It goes up non-linearly, depending more on
layer count than thicknesses owing to these boundary layer effects,
until the cells are no more than a few mm thick.

You get a static layer of air about 6 mm deep on any surface.

So one layer of clingfilm gives you one stagnant layer, multi-foils
give you multi-layer stagnancy - with proportionately better
insulation.

Foils aren't thick enough to have this 6 mm layer of air so they conduct
more heat.

That's why it's important not to press on their surfaces, or to pull
them too taut. When correctly installed, they do contain multiple
cells, each of a few mm thickness, and stagnant.

"Andy Dingley" wrote in message
...
On 28 Jul, 15:05, "dennis@home" wrote:

So there is no air to provide insulation then?

Air doesn't insulate, it transfers the heat. It's a worse transfer
medium than typical solids, so in the sense of that comparison it's an
"insulator", but it's still worse than a vacuum. In particular,
circulating air is a fairly large means of heat transfer. So to apply
the idea of "a blanket of air is an insulator", then this must be a
blanket of _still_, stagnant air, not just any old thickness of
unconstrained air.

A thicker layer of wood or plasterboard is a better insulator. A
thicker layer of air, particularly on a small scale, is a _worse_
insulator.

If you have a thick layer of air with a heat differential across it,
you'll get a convection current starting. If you can make the layer of
air thinner, still at the same temperature gradient (i.e. slicing it
up with multi-foils) then convection becomes less efficient and the
overall insulation goes up. It goes up non-linearly, depending more on
layer count than thicknesses owing to these boundary layer effects,
until the cells are no more than a few mm thick.

You get a static layer of air about 6 mm deep on any surface.

So one layer of clingfilm gives you one stagnant layer, multi-foils
give you multi-layer stagnancy - with proportionately better
insulation.

No they don't!
Are you being thick on purpose?
How does a thin foil sandwich provide many stagnant layers that are more
than 6 mm thick?
As I said in the first place they don't work, they are too thin to work as
claimed.


BTW how can you tell me air doesn't insulate in one paragraph and then tell
me it does in the next?


Foils aren't thick enough to have this 6 mm layer of air so they conduct
more heat.

That's why it's important not to press on their surfaces, or to pull
them too taut. When correctly installed, they do contain multiple
cells, each of a few mm thickness, and stagnant.

The whole thing is only a few mm thick!

On 28 Jul, 19:37, "dennis@home" wrote:

How does a thin foil sandwich provide many stagnant layers that are more
than 6 mm thick?

They aren't (indivudally), the overall sandwich is.

There's no need for an insulating air layer to be 6mm thick. That's
one value for a _maximum_ thickness of a stagnation layer in these
circumstances. Layers thinner than this will still have nearly as
much thermal resistance.

The overall foil sandwich is much thicker than this. It has several
layers, there are several air pockets.

As I said in the first place they don't work, they are too thin to work as
claimed.

How thin do you think these foils are, when correctly installed?

"Andy Dingley" wrote in message
...
On 28 Jul, 19:37, "dennis@home" wrote:

How does a thin foil sandwich provide many stagnant layers that are more
than 6 mm thick?

They aren't (indivudally), the overall sandwich is.

There's no need for an insulating air layer to be 6mm thick. That's
one value for a _maximum_ thickness of a stagnation layer in these
circumstances. Layers thinner than this will still have nearly as
much thermal resistance.

They will be proportional.. a 1 mm layer will be 1/6 as good as a 6 mm
layer.
A really thin layer will be useless.


The overall foil sandwich is much thicker than this. It has several
layers, there are several air pockets.

The number of air pockets appears to confuse you.


As I said in the first place they don't work, they are too thin to work
as
claimed.

How thin do you think these foils are, when correctly installed?

Which one?
tri-iso super 10 is about 30 mm so it is about twice as good as double
glazing, that is, not vey good.

On Mon, 28 Jul 2008 22:56:30 +0100, "dennis@home"
wrote:

There's no need for an insulating air layer to be 6mm thick. That's
one value for a _maximum_ thickness of a stagnation layer in these
circumstances. Layers thinner than this will still have nearly as
much thermal resistance.

They will be proportional.. a 1 mm layer will be 1/6 as good as a 6 mm
layer.

If heat transfer was by conduction, then it would proportional.

However air is a fluid. Heat transfer is predominantly by convection,
not conduction. It's easily mobile, yet very low density. Even at these
dimensions, convection predominates.

A really thin layer will be useless.

We could agree that as a definition of "really" thin. However these
airgaps aren't that thin (unless you squash the foil). A mm or two is
still useful.

tri-iso super 10 is about 30 mm so it is about twice as good as double
glazing, that is, not vey good.

The whole point is that this 30mm is not spent on a single gap, but
rather multiple independent airgaps. That's why they work better.