Building with earth - Gernot MINKE (1)

14.25
14.21 Vertical section
through a lightweight
mineral loam floor
14.22 to 14.23 Making a
lightweight mineral loam
floor with a loam plaster
that is water-repellent
and abrasion-resistant
14.24 Vertical section
through inclined roofs
with lightweight loam
infill
14.25 Flat earthen roofs
of a Dogon village, Shanga,
Mali
Inclined roofs filled with lightweight
loam
Commonly used tile-covered rafter roofs
can be filled with lightweight loam in order
to increase their thermal and sound insulation.
If the space created by a typical
16-cm-high rafter is filled with lightweight
loam with a density of 600 kg/m 3 and the
ceiling made of timber boards, the roof
achieves an U-value of 0.8 W/m 2 K (14.24 A).
Three solutions, B, C and D, show possibilities
for attaining higher levels of thermal
insulation, as demanded in many northern
countries.
Earth-covered roofs
In dry climate zones, flat roofs covered with
earth have been in use for centuries in traditional
rural architecture. One of the greatest
challenges when building in developing
countries is to produce successful, weatherresistant
loam roofs that might prove
durable in rainy areas. The cost of a typical
roof structure in such countries is usually
25% to 30% of total buildings costs.
Loam shingles (see chapter 7, p. 70) were
propagated in Germany in the early 20th
century, and there was even a published
standard, DIN 18957. Some traditional
loam-covered roofs and some recent experiments
with loam coatings are discussed in
this section.
Traditional roofs
In many subtropical, moderate and cold
climates, traditional flat and sometimes even
inclined loam roofs have been built for centuries.
Typical examples are the flat roofs of
the Pueblo Indians in New Mexico, USA
(see 6.3), and those of the Dogon of Mali,
West Africa (14.25).
All flat roofs are similar in construction. Tree
trunks or bamboo form the primary structural
elements. Branches and twigs are laid on
these to form a fairly dense network over
which straw loam can be rammed or plastered.
The final coarse consists of several
layers of clayey loam, usually containing a
large quantity of coarse sand; sometimes
hair, fibre or cow dung is added and carefully
smoothed.
In areas where there is little rainfall, shrinkage
cracks are not a problem. When water
enters these cracks, clayey loam swells and
seals them. Only in some cases are additional
coatings used. In Anatolia, Turkey, special
clayey soil with a high salt content is taken
from the banks of the salt lakes in order
to seal loam roofs. Due to the hygroscopic
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Designs of building elements