Robert Gammon wrote:

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

Wrong again.

Nick

News wrote:

snip
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.


Then you need to develop an understanding of emmissivity.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"CJT" wrote in message
...
News wrote:


wrote in message
...

Jeff wrote:

daestrom wrote:


From The Passive Solar Energy Handbook, Edward Mazria 1979 we have
this in Appendix E.6 Resistance values of airspaces

Horizontal, Heatflow Down
NR=Non Reflective

Thickness | Season | NR/NR | NR/Aluminum Coated | NR/Foil
3/4 W 1.02 2.39 3.55
1 1/2 W 1.14 3.21 5.74
4 W 1.23 4.02 8.94
3/4 S 0.84 2.08 3.25
1 1/2 S 0.93 2.76 5.24
4 S 0.99 3.38 8.03

Obviously that's all from observations.


With how many foils and what temp? What's the significance of "W" and
"S"
with downward heatflow? A winter floor and a summer ceiling?

What strikes me for my application at hand, insulating under staple
up
radiant, is that 8.94 for a single radiant barrier. It sure makes
foil
double bubble look good.


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.


So up-facing foils may not help much, unless they are well-sealed above.

It looks to me that I have two ways to go:

1) 3 1/2" (R 11 + R 6 or so for the radiant) fiberglass batts with a
radiant barrier wired up with wire hangers or
something similar. An airspace of an 1 1/2" or so.
2) double bubble (triple radiant)


It seems that Reflectix makes a product with no radiant effect for use
under concrete, and another with 2 foils (not "triple radiant") on the
outside. The inner layers have no foil. Other options are double-foil
polyiso board and double-sided "builders foil" in 4' rolls at 10-20
cents/ft^2 from companies like Innovative Insulation, and more costly
adhesive-backed foil, and OSB with one foil face, which might be found
on the underside of a roof.

... method two, which is what at least some staple up suppliers
provide, seems plausible. It would be easier to dust seal this and it
certainly would be easier to install.


Dust sealing the exposed upper foil would be difficult.

Have I missed something, or is this really the best app for radiant
bubble? Perhaps the only time it should be used.


Radiant barriers are good for downward heatflow (including a fridge
roof),
OK for horizontal heatflow, and poorish for upward heatflow.


In keeping heat ina house, fine for the walls, no good in the attic.

I disagree, but I'm willing to listen to your reasoning if you care to
present it.

I was just bottom lining what Nick was saying just above.

"CJT" wrote in message
...
News wrote:

snip
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.

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 wrote:


"CJT" wrote in message
...

News wrote:

snip

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.


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.


There should be no confusion.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"CJT" wrote in message
...
News wrote:


"CJT" wrote in message
...

News wrote:

snip

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.


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.

There should be no confusion.

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

"CJT" wrote in message
...
News wrote:


wrote in message
...

Jeff wrote:
snip


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.

snip

In keeping heat ina house, fine for the walls, no good in the attic.

I disagree, but I'm willing to listen to your reasoning if you care to
present it.


As I said before. Government and independent testing has shown that radiant
barriers lose much of their effectiveness if they get a layer of dust over
the foil side of them. The dust raises the emissivity to that of other
non-metallic materials ( 0.85).

In places like attics, the 'usual' installation of radiant barriers is not
across the floor, but attached to the rafters overhead, facing downward.
This avoids the dust buildup issue. Thus the radiant surface is 'aimed'
downwards to the floor space of the attic. In climates that need a lot of
A/C, this can work quite well. The solar heat gained by the roofing heats
the sheathing and rafters, but the radiant barrier prevents it from
radiating to the attic floor (ceiling of the living space). Testing for
their efficacy in such installations has gone well. Radiant barriers in
this sort of situation can be an inexpensive, easy to install way to reduce
cooling energy needs.

Sadly, for climates needing a lot of heating, the situation doesn't work so
well. Installing the radiant barrier on the rafters does little to reduce
heat loss from the attic floor (living space ceiling). One reason for this
is that attics in cold climates are deliberately ventilated to keep the
attic cool. This prevents ice damage and ice dam formation on the eaves.
Another reason for poor performance in heating climates is that with the
heat flow upwards, natural convection of air from the attic floor to the
radiant barrier far outweighs the radiant heat transfer component, so
reducing the radiant heat transfer does little to reduce the overall heat
transfer (most upward heat flow still happens from convection currents).

So, bottom line. If the direction of heat flow is upward, radiant barriers
don't work well. Either convection outweighs the radiant component, or the
surface gets contaminated with dust and requires cleaning, or both.

For downward heat flow, they can add to the overall insulation if installed
correctly.

daestrom

"News" wrote in message
reenews.net...

"daestrom" wrote in message
...

snip

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

"Robert Gammon" wrote in message
m...
News wrote:

snip

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.


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

daestrom wrote:

"Robert Gammon" wrote in message
m...
News wrote:

snip

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.


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.


A 2" thick foam board with a radiant barrier applied to the board with
the board sitting behind a brick or concrete block wall has the required
airspace in front of the radiant barrier. If HardiPlank or HardiPanel
siding products or stucco are applied over the foam board, then paying
for a radiant barrier is nonsense.

You assume that the cladding is applied directly to the foam board. Not
always true.

daestrom wrote:


"News" wrote in message
reenews.net...


"daestrom" wrote in message
...


snip


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.

I've been think about that as far as my staple up radiant goes. It
looks to me that I want to cover most of the area (perhaps all) between
joists with flashing thickness aluminum to spread the heat out. That's a
lower operating temperature for the working surface. I don't think the
emissivity is as low as foil, but probably around .08. It seems to me
that part of the joist should also be covered in a radiant barrier.

It looks like you can gain a good bit of insulation value just from
having a dead air space with an IR opaque boundary.

I see from my "Passive Solar Energy Book" That a horizontal foil
surface with heatflow down has an R value of 4.55. That would seem to
imply face nailing 1" polyiso foil covered, with the foil facing down
onto the joists. Perhaps R17 total. Does that sound about right?

Jeff































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

"News" wrote in message
reenews.net...

"News" wrote in message
reenews.net...

wrote in message
...

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.

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.