Civil Engineering Reference
In-Depth Information
world, and are often griped by more pressing life issues than painting and maintaining
our houses.
To build a structure that is reliant for strength on a skin of render, whose structural
integrity is reliant on the owner's maintenance, does not appeal to me. In that the
structural capacity of the straw bales alone are more than sufficient for most applications,
I am yet to be convinced of either the need or wisdom in transferring any load to the skin
of render over the straw bales.
Can any bales of straw be used to build a house?
I am often asked will any straw bales do the job? The answer is categorically NO! The
bales must be dry with no sign of having been wet, and ideally tight. Look for dark stains
on the straw as indication of them having been wet in the past. If you are reliant on the
straw bales to carry the roof load or provide bracing for the lateral stability of the
building, it is essential that the bales are able to carry the necessary load that will be
placed on them. Even for infill walls where there is additional bracing the bales must be
dry and tight. If you use bad bales in the wall you will have to work harder in preparation
of the wall for rendering. There will be more trimming and more filling of gaps. It really
is not worth compromising on quality. My house is over 20 squares, and used
approximately 500 bales. In 2005 bales of straw were sold for around $5.50. If you were
able to buy them from a farmer direct you might get them for $3.50. The percentage
difference is significant, however it only equates to $1000 in total. Given what you are
trying to achieve, you have to ask yourself, 'is this the place to try to save a dollar?'
Selecting straw bales
Straw baled early in the morning is stronger than that baled in the heat of the day. The
old-time farmers will tell you that the best bales of straw are baled early in the morning
up to about 10 am when there is some moisture in the straw from dew but the straw is
still dry. Straw baled in the heat of the day will crack rather than bend when forced into
the baler, thereby reducing the strength of the bale.
It is very easy to test a bale of straw for building purposes. First of all pick up the bale
by one string. If the bale stays in tact continue the examination, if not, it is probably best
to leave it for animals to bed on. Next you should check for any discoloration or
blackening of the bale, as this would indicate that the bales have most likely been wet,
which may promote the decomposition of the straw. Open up one of the bales to check
for moisture in the centre of the bale and for any musty smells.
Proof of structural carrying capacity
Engineers and building surveyors may ask for proof of the bales carrying capacity. In rare
instances I have had engineers and building surveyors request proof of the structural
carrying capacity of the bales. While this can be measured utilising a moisture metre to
ascertain what percentage of the weight is attributed to moisture, I believe that this is an
unnecessary complication. When the walls are compressed with the polyester strapping
the compression is such that any bales lacking in density will be compressed until their
