ASHRAE Journal - June 2022 - 52

COLUMN BUILDING SCIENCES
PHOTO 3 Reflective Insulation Roll Blinds. The
blinds' four layers expanded as they were pulled
down, creating four airspaces each about 1 in.
(25 mm) deep. Unfortunately, there was no practical
way of air sealing the airspaces. R-15 sounded
great to me. I was young. Queen had a hit song
" Another One Bites the Dust. " I didn't realize it was
about the thermal performance of the roll blinds.
PHOTO 4 Reflective Insulation. Reflective insulation
is different from radiant barriers. Reflective
insulation relies on enclosed air spaces to have
any benefit.
PHOTO 5 Radiant Barrier in Attic. Once attic
insulation goes above R-30, radiant barriers
provide little or no benefit. Note that the current
International Energy Conservation Code calls for
minimum attic thermal resistance of between
R-38 and R-60.
wrap with transparent aluminum
and attach the bubble wrap to glass
windows-with the appropriate
air gap-and get an additional R-6.
Excuse me a minute while I connect
with the Patent Office.
Hate to burst everyone's bubble-
pun intended-National Resources
Canada (NRCan) noted that
Canada Mortgage and Housing
Corporation (CMHC) performed
studies on reflective films such as
" foil-embedded bubble insulation "
and found that the actual thermal
resistance is " R-1.5**
where the
bubble layer is between two layers
of foil without air spaces in front of
the foil. " 4 This was done with " real
thermal performance testing " - " hot
box testing. " 5
Folks in Canada were using bubble
wrap under concrete floor slabs
arguing that the bub-required R-5
slab insulation requirement-probably
Hab's fans.
Take note Canadians-sometimes
the U.S. is on the same side as you:
the United States Environmental
Protection Agency (EPA), unequivocally
stated in 2012 that, " radiant
barrier products, as defined
by EPA in the 'Seal and Insulate
with Energy Star Definitions and
Testing Requirements Version
1.0,' are not included as a home
insulation product in the Federal
Trade Commission (FTC) Code of
Federal Regulation (CFR) Part 460
'Labeling and Advertising Home
Insulation.' " 6 " Radiant barriers do
not have R-values. " I think I already
mentioned that. They are not
insulation.
So what is going on? What is real
and what is not real? Folks did a
bunch of studies on radiant barriers
in attics (Photo 5) in the 1980s.
Two notable papers from Oak Ridge
National Laboratory7,8 showed that
once attic insulation goes above
R-30, radiant barriers provide little
or no benefit. Note that the current
International Energy Conservation
Code calls for minimum attic
**Imagine that-much like a double glazed window with an air space and low-e coatings.
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ASHRAE JOURNAL ashrae.o rg
J U N E 2022
thermal resistance of between R-38
and R-60.
In an attic we have radiant energy
transfer, conductive energy transfer
and convective energy transfer. A
radiant barrier on the underside of
the roof sheathing only affects the
radiant energy transfer. The air in
the attic is still hot or cold depending
on winter or summer, and the
attic air temperature is very much
influenced by the outdoor air temperature
and the amount of insulation-or
lack of insulation on the
ceiling. And, yes, the attic air moves
around, and that affects convective
energy transfer.
Let's talk about the color of roof
membranes and roof shingles.
Doesn't this affect radiation? Yes.
Lighter colored roof membranes are
much cooler during the summer
and not as affected by this thermonuclear
ball of energy 93 million
miles away called the sun. Isn't
this good? Yes, especially for the
life of the membrane. Recall, the
Arrhenius equation. Every 20°F
(11°C) increase in average temperature
reduces the life of the material
by 50%. So the membranes last
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