Civil Engineering Reference
In-Depth Information
Impressive-compressive
methods
(as used in California) or pairs of threaded
rod attached to the top and base plates and
screwed down (used in Australia).
As strawbale building has become more
professional, ways have been developed
of speeding up and improving techniques
to make them more appropriate for the
modern building site.The following principles
can be applied equally to loadbearing and
infill methods.
You can appreciate that putting the walls
under the amount of pressure required
to compress the bales, particularly when
using construction-grade bales of very high
density, requires a lot of force. This means
that whatever you fasten the ratchet straps
to at foundation level needs to be very
strong. For commercial house building, this
is a design detail that needs to be added in
at the earliest stages. The following are two
ways in which it can be done.
Traditionally, in loadbearing buildings the
roof weight would compress the bales
over a period of about six weeks, but by
pre-compressing the straw, settlement
caused by the roof and floor loads can be
controlled and encouraged to happen much
more quickly. Now that straw is becoming a
mainstream building material it is necessary
to be able to construct loadbearing buildings
fast and simply using pre-compression.
Various methods of pre-compressing straw
walls have been used around the world
since at least 1994. The idea is to force settle-
ment of the bales and maintain the pressure
by the use of tie-down straps, fastened
over the top of the wall and down to the
foundations. When you see this happen, it
transforms a very flexible wall into a solid,
strong, extremely
impressive
structure in
a few moments! (No-nonsense builders,
previously sceptical of this new-fangled
building material, have become instant
advocates at this point in the build and have
been found showing their friends round and
boasting about their building's credentials.)
Methods include rubber tubes placed on top
of the walls, fastened down with chains and
then filled with air (first used in Canada),
industrial-strength ratchet straps, placed
over the top of the walls and fastened to the
foundations, and then ratcheted down tight
•
Lay a 25mm (1”) water pipe through the
foundations so that when you are ready
you can insert a metal pin, about 18mm
(
¾
”) diameter, through it, which projects
about 100mm (4”) beyond each face of
the wall. Ratchet straps can then hook
on either side of the wall to this pin, the
pin can be removed later, and the hole it
leaves then pointed up.
•
Extend the width of the baseplate,
normally the width of a bale, by 50mm
(2”) and project it to the inside of the
building, so that you have a 50mm lip of
timber that can be caught by the hook
of the ratchet. On the outside face of the
timber baseplate fix a temporary 50mm x
50mm batten: this will perform the same
function and can be removed before
plastering. This method can be used
only if the baseplate is securely fastened
down to the foundations, or if the weight
of the walls above is sufficient to prevent
the baseplate from lifting under the
pressure.
