US R-values of radiant barriers

[[email protected]]

Here's one way to estimate the R-value of a radiant barrier based on the air
gap and the emissivities and surface temps and the direction of heatflow from
http://www.reflectixinc.com/pdf/RIMA_Handbook.pdf

10 SCREEN 9:KEY OFFIM HC(18,6)
20 DATA 0.359,0.184,0.126,0.097,0.080,0.068
30 DATA 0.361,0.187,0.129,0.100,0.082,0.072
40 DATA 0.363,0.189,0.131,0.101,0.085,0.075
50 DATA 0.364,0.190,0.132,0.103,0.087,0.078
60 DATA 0.365,0.191,0.133,0.105,0.090,0.081
70 DATA 0.366,0.192,0.134,0.106,0.092,0.082
80 DATA 0.360,0.204,0.169,0.179,0.185,0.189
90 DATA 0.366,0.267,0.223,0.233,0.238,0.241
100 DATA 0.373,0.247,0.261,0.271,0.275,0.276
110 DATA 0.380,0.270,0.292,0.301,0.303,0.303
120 DATA 0.387,0.296,0.317,0.325,0.327,0.326
130 DATA 0.394,0.319,0.339,0.347,0.347,0.345
140 DATA 0.381,0.312,0.295,0.284,0.275,0.268
150 DATA 0.429,0.381,0.360,0.346,0.336,0.328
160 DATA 0.472,0.428,0.405,0.389,0.377,0.368
170 DATA 0.511,0.465,0.440,0.423,0.410,0.400
180 DATA 0.545,0.496,0.469,0.451,0.437,0.426
190 DATA 0.574,0.523,0.494,0.475,0.460,0.449
200 FOR I=1 TO 18'read data table
210 FOR J=1 TO 6
220 READ HC(I,J)
230 NEXT:NEXT
240 T1=105'temperature of surface 1 (F)
250 E1=.03'emissivity of surface 1
260 T2=75'temperature of surface 2 (F)
270 E2=.8'emissivity of surface 2
280 L=2'air gap (valid range: 0.5-3")
290 LI=INT(2*L+.5)'length table index
300 HF=0'heatflow 0-down,1-sideways,2-up
310 E=1/(1/E1+1/E2-1)'effective emittance
320 TM=(T1+T2)/2'mean temp (F)
330 DT=ABS(T1-T2)'temp diff (valid range: 5-30 F)
340 DTI=INT(DT/5+.5+6*HF)'temp diff table index
350 HR=.00686*((TM+459.7)/100)^3'radiant conductance
360 R=1/(E*HR+HC(DTI,LI))'US R-value (ft^2-F-h/Btu)
370 PRINT T1,E1,T2,E2
380 PRINT L,HF,R

T1 (F) E1 T2 (F) E2

105 .03 75 .8

gap heatflow US R-value

2" 0 (down) 7.146456

With more than one space in series (eg double-foil foamboard spaced away
from a basement wall), we can't just add R-values. We only know the overall
temp diff, so we have to iterate to find a solution. It's no surprise that
the FTC prohibits makers from advertising R-values for radiant barriers
to avoid confusing the public.

Nick

 

[[email protected]]

How does this work out for the double bubble?

Haven't tried that. You might work it out, if you know the gap width, etc.

http://www.blueridgecompany.com/radiant/hydronic/189#pricing >

It seems to me there are two ways to go for the underfloor insulation
for staple up radiant.

One is foil backed fiberglass insulation with an airspace. That is hard
to find! The other would be double bubble stapled on the joists. It
seems to me that would minimize heat loss through the joists themselves
as they would be uninsulated elsewise. Any thoughts?

I would staple on foil or thin double-foil foamboard.

Nick

 

[News]

Here's one way to estimate the R-value
of a radiant barrier based on the air
gap and the emissivities and surface
temps and the direction of heatflow from

It is?

The British Advertising Standards Authority got Actis, a French company,
claiming their reflective foil insulation is 'Equivalent to 200mm of
traditional Rockwoool insulation'. A complaint has been upheld after ASA
went to independent technical experts.

The judgement can be seen at:
http://tinyurl.com/s6c2p

Think hard before you buy.

 

[m Ransley]

I dont believe Reflextic results, isn`t it amazing no other major
insulation manufacturer can capitalise on this. If there were true
independant tests I would think differently.

 

[News]

Here's one way to estimate the R-value of a radiant barrier based on the
air
gap and the emissivities and surface temps and the direction of heatflow
from
http://www.reflectixinc.com/pdf/RIMA_Handbook.pdf

10 SCREEN 9:KEY OFFIM HC(18,6)
20 DATA 0.359,0.184,0.126,0.097,0.080,0.068
30 DATA 0.361,0.187,0.129,0.100,0.082,0.072
40 DATA 0.363,0.189,0.131,0.101,0.085,0.075
50 DATA 0.364,0.190,0.132,0.103,0.087,0.078
60 DATA 0.365,0.191,0.133,0.105,0.090,0.081
70 DATA 0.366,0.192,0.134,0.106,0.092,0.082
80 DATA 0.360,0.204,0.169,0.179,0.185,0.189
90 DATA 0.366,0.267,0.223,0.233,0.238,0.241
100 DATA 0.373,0.247,0.261,0.271,0.275,0.276
110 DATA 0.380,0.270,0.292,0.301,0.303,0.303
120 DATA 0.387,0.296,0.317,0.325,0.327,0.326
130 DATA 0.394,0.319,0.339,0.347,0.347,0.345
140 DATA 0.381,0.312,0.295,0.284,0.275,0.268
150 DATA 0.429,0.381,0.360,0.346,0.336,0.328
160 DATA 0.472,0.428,0.405,0.389,0.377,0.368
170 DATA 0.511,0.465,0.440,0.423,0.410,0.400
180 DATA 0.545,0.496,0.469,0.451,0.437,0.426
190 DATA 0.574,0.523,0.494,0.475,0.460,0.449
200 FOR I=1 TO 18'read data table
210 FOR J=1 TO 6
220 READ HC(I,J)
230 NEXT:NEXT
240 T1=105'temperature of surface 1 (F)
250 E1=.03'emissivity of surface 1
260 T2=75'temperature of surface 2 (F)
270 E2=.8'emissivity of surface 2
280 L=2'air gap (valid range: 0.5-3")
290 LI=INT(2*L+.5)'length table index
300 HF=0'heatflow 0-down,1-sideways,2-up
310 E=1/(1/E1+1/E2-1)'effective emittance
320 TM=(T1+T2)/2'mean temp (F)
330 DT=ABS(T1-T2)'temp diff (valid range: 5-30 F)
340 DTI=INT(DT/5+.5+6*HF)'temp diff table index
350 HR=.00686*((TM+459.7)/100)^3'radiant conductance
360 R=1/(E*HR+HC(DTI,LI))'US R-value (ft^2-F-h/Btu)
370 PRINT T1,E1,T2,E2
380 PRINT L,HF,R

T1 (F) E1 T2 (F) E2

105 .03 75 .8

gap heatflow US R-value

2" 0 (down) 7.146456

With more than one space in series (eg double-foil foamboard spaced away
from a basement wall), we can't just add R-values. We only know the
overall
temp diff, so we have to iterate to find a solution. It's no surprise that
the FTC prohibits makers from advertising R-values for radiant barriers
to avoid confusing the public.

Nick

Rockwool has a set value and can be compounded. Makers claim all sorts of
wild claim for radiant barriers. To bottom line, what is it the equivalent
to in rockwool in thickness?

 

[News]

I think that is exactly what Nick has done. But remember fiberglass
blankets are temperature independant (mostly). Radiant barriers are
dependant on the temperature (emisivity is T^3) and the air space can be
treated as a more conventional "R" value. Note that Nick has commented the
code.

Run that for a higher delta temp and you will get a higher R, just a lower
delta temp gives a lower.

I am very sceptical of these barriers. What they need to do is have two
identical houses in the same place, one with the barrier and one with
rockwool. Then do data monitoring for a year or more. The British ASA
ruled against Actis, a French maker, as the tests were not good enough.
There is no testing model to explain. After all this time you would have
thought they could have done tests on an Actis Triso9 house and an identical
house without Actis with 200mm of insulation in the walls. If there was a
clear difference I'm sure they would be crowing from the rooftops with all
data printed and freely given out at every bus stop.

This stuff is not cheap. As far as I can see it is expensive bubble wrap -
until proper meaningful realistic independent tests have been undertaken.

 

[News]

It is?

The British Advertising Standards Authority got Actis, a French company,
claiming their reflective foil insulation is 'Equivalent to 200mm of
traditional Rockwoool insulation'. A complaint has been upheld after ASA
went to independent technical experts.

The judgement can be seen at:
http://tinyurl.com/s6c2p

Think hard before you buy.

The link above does not work. Here is the ruling:

Actis Insulation Ltd
Unit 1
Cornbrash Park
Bumpers Farm Industrial Estate
Chippenham
Wiltshire
SN14 6RA

Date: 31st May 2006
Media: Brochure

Sector: Household

Public Complaint From: Gloucestershire

Complaint:

Objection to a brochure for roof insulation. The brochure stated "TRI-ISO
SUPER 9 Insulation for roofs ... Thermally equivalent to 200 mm of mineral
wool when installed in a roof situation, as certified by the European
certifying body, BM TRADA CERTIFICATION (following real building trials,
certification n°0101) ... THERMAL EFFICIENCY equivalent to 200 mm of mineral
wood RT = 5* ... *in situ measured values." The complainant challenged:

1. the claim "Thermally equivalent to 200 mm of mineral wool" and

2. the quoted thermal resistance "RT = 5".


Codes Section: 3.1, 7.1 (Ed 11)

Adjudication:

Actis Insulation Ltd (Actis) said they had stopped advertising TRI-ISO SUPER
9 because it had been replaced with their new product TRI-ISO SUPER 10. They
said the efficiency of their products was demonstrated by their track record
in the market. Actis said they had commissioned BM TRADA Certification Ltd
(BM TRADA) to test, assess and report on the TRI-ISO Super 9 product. They
provided us with a copy of the BM TRADA Certification and Report dated
August 1997 and said that it substantiated their claims. Actis explained
that TRI-ISO Super 9 was different from traditional bulk insulation because
it was a multi-foil product that used layers of reflective foils spaced with
synthetic wadding and foams. They said the product required less space than
traditional bulk insulation and, therefore, internal insulation cavities
could be made smaller and internal useable spaces could be enlarged without
compromising efficiency of insulation. Actis argued that traditional methods
of testing were not appropriate for their product because traditional
methods measured thermal efficiency mainly by conduction and did not take
into account the influences of convection, radiation and change of phase.
They said their product combined various energy transfers of radiation,
conduction, convection and change of state rather than just conduction.
Actis also argued that traditional methods of testing did not allow
representation of the real behaviour of building materials once used on
site. They pointed out that BM TRADA had used "in situ" testing involving a
real external environment with variations in temperature, humidity, etc.
rather than the traditional methods of laboratory testing. Actis maintained
that the BM TRADA Certification demonstrated the thermal efficiency of their
product and provided proof of their claims.

1. Complaint upheld

The ASA obtained expert advice. We understood that BM TRADA had tested
TRI-ISO SUPER 9 and the mineral wool in two separate roof installations.
However, we noted that BM TRADA had not used the standard industry methods
of testing and that the report provided by Actis did not include sufficient
detail to support their own methods of testing.

We acknowledged that BM TRADA Certification was a leading multi-sector
certification body accredited by the United Kingdom Accreditation Service.
We considered that the BM TRADA report did not provide enough detail to
support their methodology instead of the methodology employed by the
internationally recognised ISO industry standards. We concluded Actis had
not substantiated the claim. We noted the ad was no longer appearing but
told Actis not to repeat the claim in future advertising until they were
able to provide sufficient substantiation.

2. Complaint upheld

We understood that RT was a symbol of total thermal resistance and typically
had the standard unit of measurement of m²K/W. We noted that the claim
"RT=5" was not qualified by any recognised units of measurement e.g. m²K/W
and a small footnote stated only "in situ measured values" without further
explanation. Because the value of 5 was not qualified by any recognised
units of measurement, we considered the claim "RT=5" was ambiguous and
should be qualified in future. However, we noted that the BM TRADA report
did specify an overall resistance (RT) of 5.0m²K/W derived from the in situ
testing. We understood that the in situ measured values did not meet with
ISO recognised international standards for determining declared and design
thermal values for building materials and products.

We considered that the BM TRADA report did not include sufficient detail to
demonstrate the validity or robustness of their testing methodology instead
of the methodology employed by ISO standards. We concluded that the report
did not substantiate the claim " RT=5". We told Actis to remove the claim
until they were able to provide sufficient substantiation.

The brochure breached CAP Code clauses 3.1 (Substantiation) and 7.1
(Truthfulness).

 

[[email protected]]

The British Advertising Standards Authority... [objected to] a brochure
for roof insulation. The brochure stated "TRI-ISO SUPER 9 Insulation for
roofs was... Thermally equivalent to 200 mm of mineral wool when installed
in a roof situation, as certified by the European certifying body, BM TRADA
CERTIFICATION (following real building trials...

... Actis said they had commissioned BM TRADA Certification Ltd (BM TRADA)
to test, assess and report on the TRI-ISO Super 9 product. They provided us
with a copy of the BM TRADA Certification and Report dated August 1997 and
said that it substantiated their claims... They pointed out that BM TRADA
had used "in situ" testing involving a real external environment with
variations in temperature, humidity, etc. rather than the traditional
methods of laboratory testing...

... We understood that BM TRADA had tested TRI-ISO SUPER 9 and the mineral
wool in two separate roof installations. However, we noted that BM TRADA
had not used the standard industry methods of testing and that the report
provided by Actis did not include sufficient detail to support their own
methods of testing.

We acknowledged that BM TRADA Certification was a leading multi-sector
certification body accredited by the United Kingdom Accreditation Service.
We considered that the BM TRADA report did not provide enough detail to
support their methodology...

.... ie they faulted the test documentation, vs the result.

We understood that RT was a symbol of total thermal resistance and typically
had the standard unit of measurement of m²K/W. We noted that the claim
"RT=5" was not qualified by any recognised units of measurement e.g. m²K/W
and a small footnote stated only "in situ measured values" without further
explanation. Because the value of 5 was not qualified by any recognised
units of measurement, we considered the claim "RT=5" was ambiguous and
should be qualified in future.

.... and they faulted the lack of explicit units in the advertised result.

However, we noted that the BM TRADA report did specify an overall resistance
(RT) of 5.0m²K/W derived from the in situ testing...

Picky, picky. Reflectix does advertise some system R-values:

http://www.reflectixinc.com/script/products/product.asp?ID=64
http://www.reflectixinc.com/script/products/product.asp?ID=77
www.majorgeothermal.com/PDFs/Reflect/Solutions.pdf

The US R16.8 crawl space number is interesting.

Nick

 

[daestrom]

The British Advertising Standards Authority... [objected to] a brochure
for roof insulation. The brochure stated "TRI-ISO SUPER 9 Insulation for
roofs was... Thermally equivalent to 200 mm of mineral wool when installed
in a roof situation, as certified by the European certifying body, BM
TRADA
CERTIFICATION (following real building trials...

... Actis said they had commissioned BM TRADA Certification Ltd (BM TRADA)
to test, assess and report on the TRI-ISO Super 9 product. They provided
us
with a copy of the BM TRADA Certification and Report dated August 1997 and
said that it substantiated their claims... They pointed out that BM TRADA
had used "in situ" testing involving a real external environment with
variations in temperature, humidity, etc. rather than the traditional
methods of laboratory testing...

... We understood that BM TRADA had tested TRI-ISO SUPER 9 and the mineral
wool in two separate roof installations. However, we noted that BM TRADA
had not used the standard industry methods of testing and that the report
provided by Actis did not include sufficient detail to support their own
methods of testing.

We acknowledged that BM TRADA Certification was a leading multi-sector
certification body accredited by the United Kingdom Accreditation Service.
We considered that the BM TRADA report did not provide enough detail to
support their methodology...

... ie they faulted the test documentation, vs the result.

We understood that RT was a symbol of total thermal resistance and
typically
had the standard unit of measurement of m²K/W. We noted that the claim
"RT=5" was not qualified by any recognised units of measurement e.g. m²K/W
and a small footnote stated only "in situ measured values" without further
explanation. Because the value of 5 was not qualified by any recognised
units of measurement, we considered the claim "RT=5" was ambiguous and
should be qualified in future.

... and they faulted the lack of explicit units in the advertised result.

However, we noted that the BM TRADA report did specify an overall
resistance
(RT) of 5.0m²K/W derived from the in situ testing...

Picky, picky. Reflectix does advertise some system R-values:

http://www.reflectixinc.com/script/products/product.asp?ID=64
http://www.reflectixinc.com/script/products/product.asp?ID=77
www.majorgeothermal.com/PDFs/Reflect/Solutions.pdf

The US R16.8 crawl space number is interesting.

An important question here is how does other insulation perform 'in-situ' if
measured the same way as this product.

If this product can achieve an RT=5 'in situ', that means the overall
measured insulative performance is 5 m^2-K/W. That performance includes the
affects of convection and radiant heat transfer from the living space to the
product, and from the product to the environs on the other side.

But what is deceptive about this, is that if I were to put a simple piece of
conventional building insulation that has an RT=5 value in the same
circumstance, it would undoubtedly have an 'in situ' performance that is
*better* than 5. Because added to the material's own RT=5, would also be
the affects of the convective layers on each side (just like this product),
and the radiant transfer to/from the surfaces.

Unless this products RT value is calculated by taking the 'in-situ'
performance and *subtracting* the insulative performance of those items
common to *all* installations, the RT value is inflated by those other
factors. Thus when compared with other materials tested in the more
traditional manner, it overstates this product's performance.

daestrom

 

[News]

The British Advertising Standards Authority... [objected to] a brochure
for roof insulation. The brochure stated "TRI-ISO SUPER 9 Insulation for
roofs was... Thermally equivalent to 200 mm of mineral wool when installed
in a roof situation, as certified by the European certifying body, BM
TRADA
CERTIFICATION (following real building trials...

... Actis said they had commissioned BM TRADA Certification Ltd (BM TRADA)
to test, assess and report on the TRI-ISO Super 9 product. They provided
us
with a copy of the BM TRADA Certification and Report dated August 1997 and
said that it substantiated their claims... They pointed out that BM TRADA
had used "in situ" testing involving a real external environment with
variations in temperature, humidity, etc. rather than the traditional
methods of laboratory testing...

... We understood that BM TRADA had tested TRI-ISO SUPER 9 and the mineral
wool in two separate roof installations. However, we noted that BM TRADA
had not used the standard industry methods of testing and that the report
provided by Actis did not include sufficient detail to support their own
methods of testing.

We acknowledged that BM TRADA Certification was a leading multi-sector
certification body accredited by the United Kingdom Accreditation Service.
We considered that the BM TRADA report did not provide enough detail to
support their methodology...

... ie they faulted the test documentation, vs the result.

We understood that RT was a symbol of total thermal resistance and
typically
had the standard unit of measurement of m²K/W. We noted that the claim
"RT=5" was not qualified by any recognised units of measurement e.g. m²K/W
and a small footnote stated only "in situ measured values" without further
explanation. Because the value of 5 was not qualified by any recognised
units of measurement, we considered the claim "RT=5" was ambiguous and
should be qualified in future.

... and they faulted the lack of explicit units in the advertised result.

However, we noted that the BM TRADA report did specify an overall
resistance
(RT) of 5.0m²K/W derived from the in situ testing...

Picky, picky. Reflectix does advertise some system R-values:

http://www.reflectixinc.com/script/products/product.asp?ID=64
http://www.reflectixinc.com/script/products/product.asp?ID=77
www.majorgeothermal.com/PDFs/Reflect/Solutions.pdf

The US R16.8 crawl space number is interesting.

Nick

They now have TRI-ISO SUPER 10, not 9, so this judgement againast them
doesn't stand anymore. They still state that it is equiv to 210mm of
mineral wool.
<http://www.tri-isosuper10.co.uk/tri-iso_super_10_thermal_insulator_test_data.htm>

I might put a complaint in.

 

[News]

One thing though about radiant barriers. It's well settled that the upper
surface of horizontal installations will not retain its low emissivity.
Unless you fancy wiping and cleaning off the dust every year or so, it
will accumulate and lose its effectiveness.

In attics, it's advised to put the radiant barrier on the rafters overhead
so the radiant surface is on the underside. For underfloor installations,
the same thing. The foil goes on the underside to limit the accumulation
of dust that will ruin its effectiveness.

I always thought the shiny side reflects, so needs to be facing where heat
needs to be reflected back and there needs to be a 1" gap between that and
any other surface. Having it under floors facing down should not be
effective. Yet I have read that some makers say it does not matter which way
it goes, I find that hard to believe.

 

[[email protected]]

I always thought the shiny side reflects, so needs to be facing where heat
needs to be reflected back

When heat radiation strikes a surface, it's either transmitted, absorbed,
or reflected. Kirchoff said "It has to go somewhere," ie T + A + R = 1. If
T = 0 (an opaque surface with no transmission), A + R = 1. If the surface
emits as much power as it absorbs, E = A, integrated over the whole spectrum
(R is an energy conservation wash.) So a foil has reflectivity 1-E, which
is large if E is small, ie it's a good heat mirror. It can stay cool because
it doesn't absorb much heat, and it won't lose much heat because it's at
a low temp and it emits poorly.

and there needs to be a 1" gap between that and any other surface.

Big gaps with less still-air conductance are good for downwards heatflow.
A 1-1.5" gap is good for sideways heatflow. Smaller gaps have more still-air
conductance and larger gaps have slightly more "convection conductance."

Having it under floors facing down should not be effective.

It should be, if there's an air gap beneath the foil.

Nick

 

[[email protected]]

... Cold climates, foil side faces towards the house to radiate heat
back to the floors.

Wrong again.

Nick

 

[News]

News wrote:



Then you need to develop an understanding of emmissivity.

I'm sure Nick will elaborate on the wheres and whys of which way it faces
for optimum performance - which is now the latest confused point on
barriers.

 

[News]

There should be no confusion.

"Should" and "is" are two different things ;-)

 

[daestrom]

I always thought the shiny side reflects, so needs to be facing where heat
needs to be reflected back and there needs to be a 1" gap between that and
any other surface. Having it under floors facing down should not be
effective. Yet I have read that some makers say it does not matter which
way it goes, I find that hard to believe.

Let me see if I can clarify it a bit for you.

Radiant heat transfer involves two surfaces. The 'hotter' one radiants
infrared energy, the 'cooler' one absorbs it. How well a particular surface
emits infrared energy when heated is measured by its emissivity.

So to reduce radiant heat transfer, we can coat the cold surface with
something that reflects infrared energy so it doesn't absorb as much. -OR-,
we could coat the hot surface with something that doesn't radiate/emit
infrared energy as well. Either one will reduce the amount of infrared
energy that gets from the 'hot' surface to the cold surface.

Now, it just so happens, that with very few exceptions, surfaces that are
poor at absorbing infrared are poor at emitting infrared. And surfaces that
are good at emitting infrared are also good at absorbing infrared. Polished
metal and metal foils are very poor at absorbing and emitting infrared. So
radiant barriers have a metalized/foil surface. There emissivity is quite
low (< 0.2, some as low as 0.05). Non metalic materials (wood, plaster,
glass wool, etc...) are good absorbers/emitters (emissivity > 0.8, often

0.9).

So, in the case of under-floor radiant barriers, if we cover the 'hot'
surface with a material that is a poor absorber of infrared (and hence is a
poor emitter of infrared), we get about the same overall affect as if we had
covered the 'cold' surface with it. We could cover either one and get about
the same affect, at least in the short term.

But once the poor absorber/emitter is covered with dust, the heat can travel
from the foil to the dust by conduction (a very good transfer mechanism).
And household dust has a very high emissivity, so it absorbs/emitts infrared
quite well. So the dust layer completely circumvents any savings of the
radiant barrier. So we *really* want to keep the radiant barrier clean.

And by putting the poor absorber/emitter on the underside, we have it in a
position (facing downward) where dust and dirt are less likely to settle on
it.

daestrom

 

[daestrom]

We're talking about the FOIL side. Its going to be shiny regardless.

With a crawl space underneath, IT MAKES LOADS of sense. But the
direction it faces is CLIMATE dependent. Cold climates, foil side faces
towards the house to radiate heat back to the floors. Hot climates, it
faces down to reflect back heat from the crawl space.

Foil, insulation, paper, or foil insulation foil are available

In new construction, you can get foam boards for sheathing that have the
radiant barrier foil attached, in some cases to BOTH sides.
www.atlasroofing.com for an example of such. A 2" board will add about
$1.15 sq ft to materials cost of the house and adds R12 to the walls.
Similar boards are available for roofs, in areas that will see water
freeze on the roof.

I think you're confusing the placement of the "vapor barrier" with the
placement of a "radiant barrier".

In construction, it is best to place the *vapor* barrier on the 'warm side'.
So in heating climates, the vapor barrier is place on the inside and in
cooling climates on the outside. The logic behind this is you want to block
the moisture that seeps through the wall *before* it cools down and has a
chance to condense.

But the foil of a *radiant* barrier can be on either the hot or cold surface
and the difference is not very much. The most important part about radiant
barriers is that a) they be positioned/installed so the foil remains clean,
b) the have an air gap facing the foil (direct contact with the next layer
makes the foil useless), c) they are only effective if air convection
against their surface is not an issue.

A 2" thick foam board with *no* radiant foil will add about R12 to the
walls. If the foamboard has a closed-cell surface coating, it can double as
a vapor/draft barrier as well. Sandwiching a foil layer between other
materials with no air gap is a complete waste of money.

daestrom

 

[News]

The link above does not work. Here is the ruling:

Actis Insulation Ltd
Unit 1
Cornbrash Park
Bumpers Farm Industrial Estate
Chippenham
Wiltshire
SN14 6RA

Date: 31st May 2006
Media: Brochure

Sector: Household

Public Complaint From: Gloucestershire

Complaint:

Objection to a brochure for roof insulation. The brochure stated "TRI-ISO
SUPER 9 Insulation for roofs ... Thermally equivalent to 200 mm of mineral
wool when installed in a roof situation, as certified by the European
certifying body, BM TRADA CERTIFICATION (following real building trials,
certification n°0101) ... THERMAL EFFICIENCY equivalent to 200 mm of
mineral wood RT = 5* ... *in situ measured values." The complainant
challenged:

1. the claim "Thermally equivalent to 200 mm of mineral wool" and

2. the quoted thermal resistance "RT = 5".


Codes Section: 3.1, 7.1 (Ed 11)

Adjudication:

Actis Insulation Ltd (Actis) said they had stopped advertising TRI-ISO
SUPER 9 because it had been replaced with their new product TRI-ISO SUPER
10. They said the efficiency of their products was demonstrated by their
track record in the market. Actis said they had commissioned BM TRADA
Certification Ltd (BM TRADA) to test, assess and report on the TRI-ISO
Super 9 product. They provided us with a copy of the BM TRADA
Certification and Report dated August 1997 and said that it substantiated
their claims. Actis explained that TRI-ISO Super 9 was different from
traditional bulk insulation because it was a multi-foil product that used
layers of reflective foils spaced with synthetic wadding and foams. They
said the product required less space than traditional bulk insulation and,
therefore, internal insulation cavities could be made smaller and internal
useable spaces could be enlarged without compromising efficiency of
insulation. Actis argued that traditional methods of testing were not
appropriate for their product because traditional methods measured thermal
efficiency mainly by conduction and did not take into account the
influences of convection, radiation and change of phase. They said their
product combined various energy transfers of radiation, conduction,
convection and change of state rather than just conduction. Actis also
argued that traditional methods of testing did not allow representation of
the real behaviour of building materials once used on site. They pointed
out that BM TRADA had used "in situ" testing involving a real external
environment with variations in temperature, humidity, etc. rather than the
traditional methods of laboratory testing. Actis maintained that the BM
TRADA Certification demonstrated the thermal efficiency of their product
and provided proof of their claims.

1. Complaint upheld

The ASA obtained expert advice. We understood that BM TRADA had tested
TRI-ISO SUPER 9 and the mineral wool in two separate roof installations.
However, we noted that BM TRADA had not used the standard industry methods
of testing and that the report provided by Actis did not include
sufficient detail to support their own methods of testing.

We acknowledged that BM TRADA Certification was a leading multi-sector
certification body accredited by the United Kingdom Accreditation Service.
We considered that the BM TRADA report did not provide enough detail to
support their methodology instead of the methodology employed by the
internationally recognised ISO industry standards. We concluded Actis had
not substantiated the claim. We noted the ad was no longer appearing but
told Actis not to repeat the claim in future advertising until they were
able to provide sufficient substantiation.

2. Complaint upheld

We understood that RT was a symbol of total thermal resistance and
typically had the standard unit of measurement of m²K/W. We noted that the
claim "RT=5" was not qualified by any recognised units of measurement e.g.
m²K/W and a small footnote stated only "in situ measured values" without
further explanation. Because the value of 5 was not qualified by any
recognised units of measurement, we considered the claim "RT=5" was
ambiguous and should be qualified in future. However, we noted that the BM
TRADA report did specify an overall resistance (RT) of 5.0m²K/W derived
from the in situ testing. We understood that the in situ measured values
did not meet with ISO recognised international standards for determining
declared and design thermal values for building materials and products.

We considered that the BM TRADA report did not include sufficient detail
to demonstrate the validity or robustness of their testing methodology
instead of the methodology employed by ISO standards. We concluded that
the report did not substantiate the claim " RT=5". We told Actis to remove
the claim until they were able to provide sufficient substantiation.

The brochure breached CAP Code clauses 3.1 (Substantiation) and 7.1
(Truthfulness).

Further to the above:

The UK authorities have pulled the plug on multifoils, when used on their
own. The Multifoil Council) made pleaded to the Office of the Deputy Prime
Minister when the last round of Part L (energy aspect) of the building regs
was being assessed and had a reprieve to 01/01/2007 to give them time to
show that multifoils worked as claimed. This repreive has been recinded
early because of convincing evidence
that the multifoil claims are exagerated. Multifoils will only be
permissable if they can pass hot box tests, which they have never have. All
the local authorities and the NHBC and such bodies have all been told to no
longer accept multifoils.

Action may be taken against the 3rd party certifiers, principally BM Trada,
who gave their stamp of approval to Actis and others.