Wool insulation is made from sheep wool that is
mechanically bonded together to form insulating batts and
ropes. Batts are commonly used in timber-frame buildings and
ropes are primarily used between the logs in log homes. Wool
insulation is used for both thermal and acoustic insulating
applications. Sheep wool is a natural, sustainable,
renewable, recyclable material that does not endanger the
health of people or the environment
[1].
Wool
is a highly effective insulating material that has been used
for years insulating people in the form of clothing.
Mongolian nomads also used felted and woven sheep wool pads
as an insulating layer on the walls and floors of their
dwellings called, ger or yurts. Presently the use of wool
for insulation is starting to rise in popularity. It is used
more in Europe, Australia and Canada than it is the United
States; manufacturers are, however, trying to expand their
distribution to the US.
Insulating
qualities
Sheep wool is a natural insulator because
it has a crimped nature which traps air in
millions of tiny pockets. Wool insulation
will keep a building up to 7 °C cooler in
warm weather and up to 4 °C warmer in cool
weather compared to buildings with other
forms of insulation[2].
Sheep wool insulation has an R-value
(resistance to heat flow) of approximately
3.5 to 3.8 per inch of material thickness[3]
[4]
which is 0.3 to 0.6 points higher than
fiberglass, cellulose, or mineral wool
[5].The
crimp also allows the wool to retain its
structure and overall thickness instead of
breaking down and settling like many other
insulating materials. Wool is a hygroscopic
material which means that it will absorb up
to 30% to 40% of its own weight in moisture
without becoming wet to the touch[1]
[2]. This moisture absorption is
unique to sheep wool and does not compromise
the wools insulating abilities unlike
cellulose or fiberglass insulation. When
used as acoustic insulation wool provides
rates starting at 44dB for a 60mm (2.4in)
thick partition, and goes up to 53dB for a
100mm (4in) thickness[1].
Wool has a long life span and can be used
over and over again. Wool also has a low
embodied energy at approximately 15 kilowatt
hours per cube meter of material produced.
The low embodied energy of wool is just over
half of that of cellulose insulation and
practically one sixth of the embodied energy
required to produce mineral wool. However,
the issues of transportation energy costs
need to be factored in, as the
embodied energy figures usually do not
consider this. Consumers must think about
both transportation stages, pre-production,
as a raw material, and post-production as
insulation, to be careful to choose a
manufacturer that is as close as possible to
the building site[6].
Health
considerations
Wool is not irritating to the respiratory
system or the skin like fiberglass and other
alternative insulating materials because its
fibers are more than 30 micrometres thick
which is too big to be a health risk;
potentially carcinogenic fibers are 1 to 4
micrometres thick. Wool insulation also
helps prevent the sick building syndrome
because it permanently traps substances like
formaldehyde, nitrogen dioxide and sulfur
dioxide emitted by other common building
materials and combustion processes[1].
Sheep wool
is naturally
flame retardant,
self extinguishing and won’t melt. In the
case that the wool does ignite, its
inflammation point is 560 degrees Celsius,
it will not emit any toxic gases. Because
wool insulation is mechanically bonded there
are no chemicals or glues needed. Sheep wool
is biodegradable so used wool insulation, if
it not going to be recycled, can be
composted without causing harm to the
environment.
Building
considerations
Wool insulation commonly comes in rolls
of batts or ropes with varied widths and
thicknesses depending on the manufacturer.
Generally, wool batts have thicknesses of 50
mm (2 in) to 100mm (4 in), with widths of
400 mm (16in) and 600 mm (24 in), and
lengths of 4000 mm (13 ft 4 in), 5000 mm (16
ft 8 in), 6000 mm (20ft) and 7200 mm (24
ft). The widths of 16 in and 24 in are the
standard measurements between studs in a
stud frame wall. Most manufacturers provide
custom sizes as well and batts and ropes are
easy to cut once on site. Wool insulation
can be used in the roof, walls and floors of
any building type as long as there are
spaces to put the insulation in. The
construction costs when installing wool
insulation are lower due to having no need
for protective clothing or respiratory
equipment. Installing wool insulation is
very similar to installing conventional
insulation batts, it can be held into place
with staples or it can be friction-fit which
involves cutting the insulation slightly
bigger than the space it occupies, using
friction to hold it in place.
