Civil Engineering Reference
In-Depth Information
usually 100mm x 50mm (4” x 2”), are located
at intervals and either side of window and
door openings and are designed such that
the timber wallplate or roofplate, at first
floor and/or roof level, can be slotted down
on to the posts once the straw is in place
and the bracing and props are removed
(illustrated opposite), allowing the bales to
be pre-compressed manually using various
different methods. This could be by ratchet
straps, or threaded rod can be used, depend-
ing on the design. Compression of the straw
is essential to achieve enough stability of the
walls for structural integrity and so that they
can be plastered. In two-storey buildings the
first floor needs to be lowered before the
first-floor walls are installed so that the posts
have free movement through the wallplate.
The posts do not become fully structural
until the walls have been compressed and
then the timber is permanently fixed to the
wall and roofplates.
years ago in Canada, Louis Gagné pioneered
a bale building method using cement mortar
between the bales, called the Mortared Bale
Matrix. The bales were used much more like
bricks, stacked in vertical columns so the
cement mortar, in effect, formed posts
between each stack and the whole building
was cement-rendered inside and out. This
approach is rarely used now because of the
knowledge of simpler, more environmentally
conscious and more enjoyable methods, but
it is occasionally practised, particularly in
France, through the French connection
between Quebec and Europe.
In Germany they suffer from having
prescriptive Building Regulations (unlike
ours, which are guidelines), which means
they are not officially allowed to build using
the loadbearing method. This is limiting
in terms of being able to experiment and
to use new and simpler techniques. They
have to use straw as part of a timber frame
method, instead of the other way round,
and follow official practice for timber frame,
which means placing a horizontal timber
between posts at every fourth course, on
top of the straw. In practice they use this
to compress the straw in another version
of the compressive frame technique, which
works very well.
Hybrid and other methods
There are many types of straw building that
use a combination of ideas from the above
techniques, or use new ideas. Being so
simple, using straw allows for invention
during practice. For instance, it's possible to
build well-insulated loadbearing walls to
protect your house on the cold north side and
combine this with a framework method on
the south, allowing for lots of windows to
maximise solar gain. The two-storey house
that won the Grand Designs Eco-Home of the
Year Award 2008 was designed like this. All it
takes is a bit of design ingenuity to make the
rigid parts work with the flexible parts.
Other methods have been used at different
times around the world too. For instance, 30
There are many types of strawbale building
that use a combination of ideas from different
techniques, or use new ideas. Being so simple,
using straw allows for invention during
practice.
