GBlist: Mud Walls Give Poor Insulation

[Kristian Kicinski <kkicinski@robertsonsherwood.com>]

I found this article intersting- any comments?
Reposted from  http://www.farmindex.com.au/goto.cfm/8509

Mud walls give poor insulation: CSIRO

                Thursday April 27 2000

                CSIRO researchers have made a surprising discovery in
tests on mud walls,
                finding they provide poor insulation.

                Latest tests by CSIRO have confirmed that rammed earth
walls have poor
                thermal resistance - adding hard facts to the debate
about their insulation
                properties.

                CSIRO says this raises the question, "Why do so many
Australians believe earth
                construction provides such a comfortable home?"

                The research, conducted by CSIRO and funded by the
Western Australian Office
                of Energy, also produced results that effectively end
the controversy over the
                accuracy of previously published data for the thermal
resistance of rammed
                earth walls.

                "Our findings were based on testing of two
commercially-produced rammed
                earth products, both of which turned out to have poor
thermal resistance,"
                says Mr Robin Clarke of CSIRO Thermal & Fluids
Engineering (T&FE).

                "CSIRO's tests confirmed that the overall thermal
resistance (R-value) of a
                typical rammed earth wall is less than R 0.4, the same
as the disputed values
                provided for by standard design tables.

                This is low compared to everyday insulating materials
such as glass fibre batts
                which typically come with ratings of R 2 or R 3," he
says.

                "The tests used sample panels 200 mm thick, about one
metre-square and
                weighing over 400 kg. These were tested in CSIRO's one
metre square heat
                flow meter apparatus - a new record for the size and
weight of panels tested
                on our rig".

                It has been suggested that the high 'thermal mass' of
rammed earth and mud
                brick constructions compensates for their low R-value.
There may be some
                truth in this for milder or warmer climates where
massive walls are able to
                smooth out hotter days and cooler nights creating a
comfortable average. For
                climates with long periods of cold weather, however, it
is the R-value which
                largely determines the heat flow through the wall".

                Other studies have shown that walls with high mass
combined with high
                R-value can perform especially well but, unless the
climate is relatively mild, high
                mass is of little value if the wall does not also have a
high R-value.

                "While environmental, aesthetic and cost considerations
may inspire people to
                build from these materials, our results show that simple
rammed earth walls
                may not perform as well as we would like to think," Mr
Clarke says.

                These results are important as Australia moves towards
                mandatory-minimum-energy-performance-requirements in the
Building Code of
                Australia for houses and other buildings.

                Local regulations already exist in Victoria, ACT and SA.
These regulations focus
                on R-value as the principal factor. For example, in
Victoria the minimum
                acceptable overall R-value for a wall is R 1.3. From
standard design tables (now
                confirmed as accurate), the rated overall R-value of
typical rammed earth wall
                would be less than 0.5.

                Mud brick is closely related to rammed earth but
slightly less dense and slightly
                better insulating. Based on the rammed earth
measurements, the data for mud
                brick must also be regarded as reliable, suggesting an
overall R-value for a
                300-mm mud brick wall of less than 0.6. It would require
only 20 mm or so of
                most insulation materials to achieve this same
performance.

                There is a current exemption in some regulations for
walls thicker than 180
                mm, not because of the acceptable thermal performance of
these walls but
                because established constructions such as double brick
and rammed earth or
                mud brick are difficult to insulate.

                Mr Clarke points out that their poor R-value would make
most earth
                constructions illegal if it were not for the temporary
thickness exemption.

                "In developing an energy code for Australian houses, we
urgently need to
                consider whether other factors (such as high mass) are
able to compensate for
                the low R-value. We are considering the use of
mathematical modelling to look
                more closely at the way heavyweight houses respond to
typical Australian
                climates," he says.

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