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Radiant Barrier problem

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Posted by The Quintessential Man... on October 8, 2006, 1:21 am
I put this up on alt.home.repair but I thought I would try here too.

I have a problem concerning my radiant attic barrier that I don't have
the background to resolve.

At the start of the summer I had a radiant barrier coating (e.24, 76%
efficient) installed in my house attic.  I already had mechanical
ventilation (although not enough) and was forestalling the installation
of more ventilation until I got the numbers back on the performance of
the radiant barrier (Radiance brand.)  I have an attic of similar
construction and orientation over my detached garage that has no barrier
and little if any ventilation.  I installed thermistor temperature
sensors connected to a data logger in both attics at similar locations
and log the temperature 24/7.  The temperature curves, with respect to
time, are virtually identical.  The exception is that the barrier attic
seems to heat up a little faster until the fan comes on at which point
the two curves line up; it is as though it is trapping heat.  Even if
the issue is lack of ventilation, as the contractor contends, should I
not still expect to see a lag in the temperature rise over time in the
treated attic as opposed to the untreated attic.  I have also taken
interior surface (underside of decking) readings with an infrared sensor
(Fluke 61) and detect no noticeable difference.

Either I am measuring this wrong or the barrier is not working.  The
contractor's expertise seems to be more on the area of installation and
less in troubleshooting.  They seem convinced that I need more
ventilation, but if that is the case of what value is the radiant
barrier, I would just merely add a bigger fan...  The only real
advantage I can detect from the barrier so far, is that one lone light
bulb really brightens up the attic now...!

Please help


Posted by samuel chamberlain on October 8, 2006, 8:10 pm
The Quintessential Man... wrote:

I am not any type of expert in this area just so you know before hand .
have you tryed shuting off the fan ventilation ?
the efectiveness of radiant barrers depends on installation method so
have you any of the rappings to check that it has been installed in
acordence with maunfactors advice ?
hope this helps .

Posted by samuel chamberlain on October 8, 2006, 8:23 pm
 samuel chamberlain wrote:

urrr that one slipped thought the spell check ! sorry ...

Posted by SJC on October 8, 2006, 8:34 pm
 Maybe I misunderstand your post, but I thought radiant barriers were used
to reflext IR energy back to keep the house warm. Or am I missing something?

Posted by The Quintessential Man... on October 9, 2006, 12:29 am
 According to my research, the radiant barrier is supposed to reflect
radiant heat regardless of the direction.  (Know the joke about the
little boy and the thermos bottle? The little boys said: " I know it
keeps hot things hot and cold things cold, but how does it know?)  One
of the downsides to putting the barrier in the attic is that it cuts
down on solar gain in the winter, but down here in Sunny Dallas Texas
staying warm is generally not a problem, however staying cool is another
thing entirely during the 100+ degree summers.  During August my attic
got to 130+ almost every day and occasionally to 140, that was with the
barrier hence my suspicion that it is not working.  My detached garage
attic, without a radiant barrier or ventilation, measured the same
temperatures at the same times.  The problem is that I did not have the
sensors installed prior to the installation of the barrier, so I can
only compare the two similar spaces; I don't have any historical data
from years past.  But using the garage as a control, the time and
temperature curves are virtually identical.

I contacted the manufacturer once, but that product has been purchased
by a large German chemical company.  I asked the person that I got
through to how to the measure the effect, but he said only that it was
very complicated...

The installation is what I am questioning.  The paint has good coverage,
but for some reason it does not seem to reflect any heat.  I questioned
the installer on that bringing up things such as painting 20+ year old
OSB without using primer (it is my understanding that the liquid part of
the paint contains small flecks of aluminum that have to lay flat as the
paint dries; I don't know if it affects the performance if the paint
dries too fast or gets sucked into the wood before it dries properly...)
or the possibility that the mixture ratio was incorrect.  The installers
expertise seems to be in the area of applying an even coating and not
anything else related to the barriers function.  At least that is my


SJC wrote:

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