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Team Germany
(Technische Universität Darmstadt)
If you built new or renovated an
existing house today,
what kind of insulation would you put in and where? Is
fiberglass insulation still good? If not, what are the options?
Fiberglass
Fiberglass
batts are the most common insulation in the market today. They are
relatively inexpensive, easy to install and a
reasonably good insulator. So, if it's used so
widely and is a good insulator, why is it not making homes more energy efficient by
today's contemporary standards?
Well, the problem with them is that they are very easy to
install improperly. They never fully fill out the space between the
studs. So, why is that bad? When stud bays have any cavities
in them, due to thermal differences between two sides of the wall
heat would travel from hot to cold and cause convective currents
in the stud bays. This is bad for your heating and cooling bills
since convection helps transfer energy faster from hot to cold areas
(and vice versa) in your house. Many contractors today have completely stopped using
fiberglass batts. Instead they have turned to other, more effective
insulation technologies.
Spray-In Foam
Open Cell Foam
Open
cell foam is one of those new technologies. It is a water-based
spray-in foam-based insulation
made by manufacturers like Icynene.
The
foam is
sprayed in the stud bays and as it dries, it expands to fill in
every little cavity in the bay, even around the pipes, wires and
other obstructions. The complete sealing of the wall cavity prevents
any air infiltration, convective loops and reduces potential for
condensation, mold or mildew. Because of its
open-cell structure, Icynene allows for
bi-directional drying of the wall assembly through
vapor diffusion.
It is also a good noise blocker and
shows thermal performance improvements up to 50% better
then traditional fiberglass batts. Icynene is considered a green component
since it contains no CFCs, HCFCs, formaldehyde or other volatile
organic compounds (VOCs).
Measure of
material's heat-conducting properties: Heat
conduction rate per unit surface area per unit
temperature difference between its two sides.
How
do I convert U-Value from SI units to
English units?
Divide the SI number by 5.678. For example, If U=1.4
W/m²K
in SI units, then 1.4/5.678 = 0.246 Btu/hr-sf-°F in
English units.
Conversely to convert from English to SI, multiply
by 5.678: 0.246*5.678 = 1.4 W/m²K.
What is R-Value?
R
= 1/U-Value
A measure of the
capacity of a material, such as insulation, to
impede heat flow, with increasing values indicating
a greater capacity
R-Devaluator
Explore a short animation from
Icynene
which illustrates the effects of improper insulation
installation and how R-value can be diminished after
installation.
To begin, simply click the advance button at the bottom left of
the presentation screen. Please continue to use this button to go
through the presentation.
Another
type of foam that I came across is a
closed-cell foam. One of the
manufacturers of the closed-cell
foam,
Air Tight Insulation,
claims that this type of foam
presents some key advantages over
the open-cell kind.
Namely, closed-cell foam has an
R-value of 6.8 per inch (as opposed
to 3.5 for open-cell). It also forms
a complete air and moisture barrier,
and manufacturer claims it adds to
structural stability of the home.
With such qualities, it seems not
necessary to spray the foam to
completely fill the stud bay cavity.
With R 6.8 value, it is sufficient to
spray only few inches of foam in the
cavity. If you spray a thicker layer
then that, according to the AirTight
Sales Rep it wastes homeowner's
money.
There are other
kinds that are worth mentioning, such as
blown in cellulose and even
recycled denim cotton insulation, and you can read about them
further down the page.
Most Effective Way to Insulate
The
most effective way to insulate, that
is being practiced already for years
in Europe and is catching on here in
the US, is actually to place the
insulation on the outside of the
wall!
Why insulation on the outside of the wall?
While researching insulation
practices in Europe, it became apparent that
the most preferred method was the insulation
on the "cold" side of the wall - the outside.
It made sense to me how
one of the insulation manufacturers in the
UK (Celotex
www.celotex.co.uk) justified it:
"Solid timber, in the form of
studs, lintels, head rails and sole plates,
as well as intermediate floor joists and
trimmers, usually accounts for more than 20%
of the external surface area of the
building. Therefore, often less than 80% is
actually insulated. As demand for higher
standards of insulation grows, the space
between the studs becomes the limiting
factor; the timber itself acts as a thermal
bridge and the cost of increasing timber
sizes to allow more insulation to be added
is disproportionate to the improvement
achieved. Because of these thermal bridging
problems, it is now clear that higher
U-values can only be achieved by fixing the
insulation on the outside of the frame, and
covering the entire surface, both voids and
studs. The insulation is much thinner,
leaves the voids between studs free for
services and eliminates the risk of
interstitial condensation within the frame
completely. No internal vapor check is
necessary."
Besides
from limiting the thermal bridge
factor, insulation on the outside keeps the thermal mass of
the wall on the inner warm side,
well protected from moisture and
frost. As you can see from the image
on the left, in a traditional stud wall
- where insulation is only placed in-between the
studs - the thermal gradient shows that the freezing
point is actually inside the wall (68°F in the room
and 14°F outside).
If
we place the insulation on the outside, the freezing
point then moves to the outside of the wall, within
the insulation itself. That way, the inner wall
surface is at a higher temperature and gradient
inside the wall is not so steep as it is in a
traditional case. Result is
a more comfortable environment and
higher energy savings. This approach
also removes
unpleasant convective air currents
along the inner surfaces of walls
that are caused by temperature
differences (68°F-53°F as shown in
left image) between the
air in the room and actual inner wall
temperature.
For
complete information, please refer to the
table below which provides an overview of most of the
available insulation forms, insulation materials,
their installation methods, where they're applicable
to install in a home, and their advantages.
