|
One of the fairy
tales of our time is the "R-value." The "R-value" is
touted to the American consumer to the point where
it has taken a "chiseled in stone" status. The
saddest part of the fairy tale is the
R-value by
itself is almost a worthless number.
It is impossible to define an insulation with a
single value or factor. It is imperative we know more than a
single "R" value. So why do we allow the
R-value
fairy tale to be perpetuated? I don't know. I don't
know if anybody knows. It obviously favors fiber
insulation. Consider the
R-value of an insulation
after it has been submersed in water or with a 20
mile per hour wind blowing through it. Obviously the
R-value of fiber insulations would go to zero. Under
the same conditions, the solid insulations would be
largely unaffected. Again
R-value numbers are
"funny" numbers. They are meaningless unless we know
other characteristics.
None of us would ever buy a piece of property if we
knew only one dimension. Suppose someone offered a
property for $10,000 and told you it was a seven.
You would instantly wonder if that meant seven
acres, seven square feet, seven miles square, or
what. You would want to know where it was -- in a
swamp, on a mountain, in downtown Dallas. In other
words, one number cannot accurately describe
anything. The use of an
R-value alone is absolutely
ridiculous. Yet we have Code bodies mandating
R-values of 20's or 30's or 40's. A fiber insulation
having an R-value of 25 placed in a house not
properly sealed will allow the wind to blow through
it as if there were no insulation. Maybe the R-value
is accurate in the tested material in the lab, but
it is not even remotely part of the real world. We
must start asking for some additional dimensions to
our insulation. We need to know its resistance to
air penetration, to free water, and to vapor drive
(U values and K
values).
What is the R-value after it is subjected to real
world conditions?
The R-value is a fictitious number supposed to
indicate a material's ability to resist heat loss.
It is derived by taking the "k" value of a product
and dividing it into the number one. The
"k" value
is the actual measurement of heat transferred
through a specific material.
Test to Determine
the R-Value
The test used to produce the
"R" value is an ASTM test.
This ASTM test was designed by a committee to give us
measurement values that hopefully would be meaningful. A
major part of the problem lies in the out dated design of the
test. The test favors the fiber insulations --
fiberglass, rock wool, and cellulose fiber. Very little
input went into the test for the advanced solid insulations
of today, such
as foam glass, cork, expanded polystyrene or urethane
foam.
The test does not account for air movement (wind) or any
amount of moisture (water vapor); the
U factors, K
factors or C factors of state-of-the-art
insulations. For instance, fiberglass is
generally assigned an R-value of approximately 3.5. It
will only achieve that R-value if tested in an absolute
zero wind and zero moisture environment. Zero wind
and zero moisture are not real-world. Our houses
leak air, all our buildings leak air, and they often
leak water. Water vapor from the atmosphere, showers,
cooking, breathing, etc. constantly moves back and forth
through the walls and ceilings. If an attic is not
properly ventilated, the water vapor from inside a house
will very quickly semi-saturate the insulation above the
ceiling. Even small amounts of moisture will cause a
dramatic drop in fiber insulation's R-value -- as much
as 50 percent or more. Vapor Barriers
We are told, with very good reason, that insulation should
have a vapor barrier on the warm side. Which is the warm
side of the wall of a house? Obviously, it changes from
summer to winter -- even from day to night. If it is 20 F
below zero outside, the inside of an occupied house is
certainly the warm side. During the summer months, when the
sun is shining, very obviously the warm side is the outside.
Sometimes the novice will try to put vapor barriers on both
sides of the insulation. Vapor barriers on both sides of
fiber insulation generally prove to be disastrous. It seems
the vapor barriers will stop most of the moisture but not
all. Small amounts of moisture will move into the fiber
insulation between the two vapor barriers and be trapped
promoting mold. It
will accumulate as the temperature swings back and forth.
This accumulation can become a huge problem. We have
re-insulated a number of potato storages which originally
were insulated with fiberglass having a vapor barrier on
both sides. Within a year or two the insulation would
completely fail to insulate. The moisture would get trapped
between the vapor barriers and saturate the fiberglass
insulation to the point of holding buckets of water. Fiber
insulation needs ventilation on one side; therefore, the
vapor barrier should go on the side where it will do the
most good.
The
best known solid
insulation is expanded
polystyrene or
polyurethane. Other solid
insulations include cork, foam glass and polyisocyanate
or polyisocyanurate board stock. The latter two being
variations of urethane foam. Each of these insulations
are ideally suited for many uses. Foam glass has been
used for years on hot and cold tanks, especially in
places where vapor drive is a problem. Cork is of course
a very old standby often used in freezer applications.
EPS or expanded polystyrene is seemingly used everywhere
from throw away drinking cups and food containers to
perimeter foundation insulation, masonry insulations,
and more. Urethane board stock is becoming the standard
for roof insulation, especially for hot mopped
roofs. It
is also widely used for exterior sheathing on many of
the new houses. The R-value of the urethane board stock
is of course better than any of the other solid
insulations. Solid insulations will
always perform
far better than fiber insulations whenever wind
or moisture is involved.
Some
solid insulations are placed as sheets or
board stock. They suffer from one very common problem.
They generally don’t fit tight enough to prevent
air
infiltration. It does not matters how thick these board
stocks are if the wind gets behind it. We see this often
in masonry construction where board stock is used
between a brick and a block wall. Unless the board stock
is actually physically glued to the block wall air will
infiltrate behind it. In this case as the
air flows
through the weep holes in the brick and around the
insulation it is rendered virtually useless. Great care
must be exercised in placing the solid insulations. The
brick ties need to be fitted at the joints and then
sealed to prevent
air flow behind the insulation.
The only commonly used solid insulation that absolutely
protects itself from air infiltration is the
spray-in-place polyurethane. When it is properly placed
between two studs or against the concrete block wall or
wherever, the bonding of the spray plus the expansion of
the material in place will effect a total seal. This
total seal is almost impossible to overestimate. Most of the heat loss in the walls of the home
have to do with the
air seal rather than the insulation.
For physical reasons, heat does not conduct horizontally
nearly as well as it does vertically. Therefore, if
there were no insulation in the walls of the homes, but
an absolute airtight seal, there would not necessarily
be a huge difference in the heat loss. This would not be
the case if the insulation was missing from the ceiling.
Air infiltration can most effectively be stopped with
spray-in-place polyurethane. It is the only material
(properly applied) that will fill in the corners, the
cripples, the double studs, bottom plates, top plates,
etc. The R-value of a material is of no interest or
consequence if air can get past it.
Anecdotes
During the 1970 our firm insulated a bunch of new homes with 1.25 inches of
spray-in-place polyurethane foam in the walls. In 1970
the popular number for the R-value of one inch of
urethane foam was 9.09 per inch. Using this value, we
were putting an R of 1.25 x 9.09 = 11.36 in the walls.
This was much less than the R = 16 claimed by the
fiberglass insulators. Today, using the charts from an ASHRAE book, we would only be able to claim an R-value
for the 1.25 inches of 7.5 to 9. Neither of these
numbers make for a very big R-value. The reality is that
the people for whom we insulated their homes invariably
would thank us for the savings in their heat bills. They
would tell us their heating bill was half of their
neighbor's. They felt as if they saved the cost of the
polyurethane in one, or at most two, years. This is
anecdotal evidence, we know, but anecdotal evidence is
also compelling and very real in our world. Most of
these customers were savvy people. They would not have
paid the extra to get the urethane
spray foam insulation if it had
not been better.
There is a problem with
loose-fill fiberglass attic insulation is cold climates.
It appears that, as attic temperature drops below a
certain point, air begins to circulate into and within
the insulation, forming "convective loops" that increase
heat loss and decrease
In full-scale attic tests
at Oak Ridge national Laboratory, the R-value of 6
inches of cubed loose-fill attic insulation
progressively fell as the attic air temperature dropped.
At -18 F, the R-value measured only R-9. The problem
seems to occur with any low-density, loose-fill fibrous
insulation.
Nisson, J.D. Ned, JLC, "Attic Insulation Problems In
Cold Climates" March 1992, pp 42-43 the effective
R-value. At very cold temperatures (-20F), the R-value
may decrease by up to 50%."
With the lowest
k-factor and the highest R-value, urethane foam can
provide more thermal resistance with less material than
any other insulation.
About mid 1975 All Tech Insulation received
a call from a division manager of one of the major
fiberglass insulation manufacturers. The caller asked,
"I understand that you are spraying
polyurethane in the
walls of homes?" We told him that was true. He was
calling because we were cutting into the fiberglass
insulation sales in his area. He asked,
"How can we do
it?"
We knew what he meant. He wanted to know how we could look
somebody in the eye and sell them a more expensive
insulation than the cheap old fiberglass. We told him the
way we did it is with a spray gun. Of course, that wasn't
the answer he wanted. He wanted to know how we could not
feel guilty. We told him of insulating one of two nearly
identical houses built side by side. We insulated the
walls of one with 1.25 inches of
urethane. The other
house was insulated with full thick fiberglass batts put
in place by a reputable installer. Not only did we use
only 1.25 inches of
urethane as the total wall
insulation, but we had the builder leave off the
insulated sheathing. At the end of the first winter, the
urethane insulated home had a heating bill half of their
neighbor's. We know that is not terribly scientific, but
it is very real. We're not sure he was convinced, but it
should be noted that same company jumped into the
urethane spray foam insulation supply business the next year.
One and a quarter inch of
polyurethane sprayed properly
in the wall of a house will prevent more heat loss than
all the fiber insulation that can be crammed in the
walls -- even up to an eight inch thickness. Not only
does it provide better insulation, but it provides
significant
additional strength to the house.
One of our early clients was Brent. All Tech Insulation had insulated
several potato storages for him. He knew what
spray-in-place foam urethane insulation could do. When he
decided to build his new, very large, very fancy new
home, he asked All Tech Insulation to come insulate it.
We told him we
would be delighted. The builder pitched a fit. He
"didn't need any of that spray-in-place
foam urethane
insulation in his
buildings. He made his buildings
air tight, and fiberglass
was just as good."
Brent explained to the builder, "I know who is going to
insulate the building. It is not as definite as to who
is going to be the contractor. You can make up your
mind. We are going to have the urethane
spray foam insulation and
you build the building, or we are going to have the
urethane spray foam insulation, and I will have someone else build
the building." It didn't take the contractor long to
decide he wanted to use All Tech Insulation and have us
install urethane
spray foam insulation.
Contact an All Tech Insulation
engineer today (989-826-9999) for a deeper discussion
about your insulation requirements.
|
