|
One comment made was that there is little overall difference
in cost between loadbearing and infill. That does not make
any sense! With both methods, bale connecting pins, and
topplates are required. However, infill requires a timber
frame, either stud frame or post and beam to be built. Load
bearing uses 10-12mm metal rod or 2.5mm fencing wire at about 3-4 foot intervals to tie
the topplate to the footing, and thus tension the walls. I
fail to comprehend how a timber frame can cost less than 80
or 90 metres of rod at $1.20 per metre or fencing wire at about 10cents per metre - not just in
material cost, but in the labour hours and level of skill
and use of tools required to build such a structure. The
tensioning system goes up with the walls. They are not a
separate job on their own. Thus the load bearing
method stays accessible to the unskilled but keen
builder.
The other point to be considered is the utilisation of
resources. Timber is a precious commodity. To keep it out of
the wall structure means using less of it. This means
harvesting less timber; making less do more. To those who
advocate salvaged timber - yes, up to a point, but recycling
is a short term non-sustainable industry. My bet is that we
will run out of timber frame houses before we run out of
forests to fell. So recycled timber, and new timber for that
matter, would be better used selectively, not wasted in a
structural double up. It is a dwindling resource that
requires careful management.
To those who advocate steel framing, surely that flies in
the face of a sustainable, low energy, low impact approach
to our environment. Again, especially when structurally it
is unnecessary.
One strategy used in the infill method is to stack the bales
on edge. This uses less bales and cuts the cost. But
does it? It uses 15-20% less bales, but creates a new
dilemma. The render mix will not adhere directly to the
smooth sides (top and bottom of bale) without reinforcement.
So into the equation comes rolls and rolls of chicken wire,
and hours of tedious sewing and stitching. Absolutely no
gain, and with an added complication and cost factor.
One other small point. Being able to put the roof on before
the walls go on is something of a furphy. Strawbale building
is a fair-weather activity, with speed of wall raising and
rendering the essence. If this is all planned and organised
properly, this process of raising the wall and fitting the roof should take days, not months, thus
reducing the risk of untoward weather interrupting work. Once the roof is on it speeds up the final compression of the bales, and rendering can take place sooner. Don't panic if an unseasonal shower hits at this point. The bale tops are protected, and the bale walls shed water remarkably well.
Once the first coat of render is on, the walls are
reasonably safe.
Obviously, design considerations have to be taken into
account. If a wall is to be higher than usual, have more
than 50% of its area as openings, or if the building span is
greater than 5-6 metres, then a frame structure with infill
needs to be considered. But it comes back to designing
within the limits of the building material. All building
materials have their structural and loading limits.
Load-bearing encourages a smaller scale, owner- builder
friendly, low cost approach to housing. This is where
another factor becomes obvious - a smaller building costs
less than a larger one. Not always in a proportional sense,
but definitely in the final absolute cost. How often has it
happened that someone figured out that they can build their
home for half what it would cost to build normally, and then
be tempted to double the size of the house. Hey, twice the
house for the same cost! Fatal mistake, greed can be a
terrible thing. It is about time we gave more than lip
service to the concept of living and building within our
means and needs. Keeping buildings simple and to a human
scale reduces their costs.
On the structural side of things, it was noted that a good
deal of concern seemed to be directed at earthquake
resistance. This stems from the existance of a seismic belt
that runs north-south about 100-150km east of Perth. It is a
relatively quiet belt with only occasional movements, often
centred near Meckering. The general view seemed to consider
this a risk, and advocated timber framing with infill over
load bearing. However, if there is one area in the world
that knows about earthquakes, and has a stringent approach
to standards and regulations, its California. Yet California
adopted load-bearing guidelines for its building codes in
1995. By early 1996 three counties had signed them into
their building codes. Although it doesn't seem that specific
seismic testing has been conducted on strawbale structures,
the successful passing of a number of structural tests, and
the wealth of anecdotal evidence, particularily from
Wyoming, indicates that loadbearing strawbale structures
have the ability to cope with very active seismic areas. New
Zealand, also with violent geological history, has been
doing a lot of work on strawbale, to the extent that a two
storey load bearing building has been completed.
The structure of a load bearing building is totally tied
together. The roof is attached directly to the footings.
This is also an advantage in areas with high wind velocity.
Every bale is pinned to six other bales. The system is not
monolithic like brick, or rammed earth. It can bend, twist,
flex and absorb energy, but not break like a masonry wall.
It is the old story of the reed and the oak.
A timber structure works in a similar way - it also has the
ability to flex and absorb energy. However, because the wall
bales in infill are not tensioned, or are not absorbing the roof load they are not so able to
absorb and thus spread over a wider area the energy and the
forces acting on the building. It is still a far more
satisfactory method of building than monolithic
construction, but as load bearing has the proven structural
integrity, and the timber framing loses out in the costing,
it means that load bearing is still the superior method.
What it boils down to is not the building method itself, but
the nervousness that afflicts various experts and officials
when confronted with something unfamiliar to their training
and experience. This is not to be unexpected. Yet in all my experience dealing with building inspectors I have not yet come across a negative one. To approve
something, they need proof that it does work. The problem
for any new or revived building technique is to become
officially recognised. It was like this for mud bricks
thirty years ago, and for rammed earth more recently. I
guess load-bearing just has to go through a similar
gestation period. As someone once said, "The hardest million
dollars to make is the first!" It is the same for
alternative building - the hardest hurdle to clear is the
first one. Once you have made it over that first hurdle,
then you are in the race to get your approval. And this is
where my diappointment arose at the meeting. The message
seemed to be to avoid that first hurdle, to go around around it
and run in a different and easier race. All too easy, yet in
the long term, quite damaging. Sooner or later load bearing
strawbale needs to be recognised as valid and viable
building system, and that will take a lot of determination
and hard work. The risk is that if it is promoted as the
secondary method of strawbale building, and not as the
primary one, then it will prove progressively harder to make
up lost ground and get it approved across the board.
|
