[Strawbale] Re: Straw Bale Castle

Chris Mowatt ChrisMowatt at i12...
Wed Jul 30 14:24:03 CEST 2003


Thanks for your comments. Its good to see that our little project is
provoking some interest. What we are proposing is radical and
risky, so we expect a lot of negative comments and questions about
our sanity. We are seeking information and constructive criticism,
though a few kind words of encouragement are always welcome.

> I wish you best of luck.  You have recognized the possibility of
> spectacular failure.  I am surprised that you are willing to bet such
> a large amount of money on the project, at such long odds, but I am
> often surprised by earthlings.
It's only a gamble if failure is unprofitable. We reckon the free publicity
would cover the financial costs of failure. Long odds? I'm not convinced
the odds are that long. With the right approach, almost any practical
difficulties can be overcome, although usually at some expense. Say, for
example, we build our straw bale castle, but the rain pisses in - we still
have the perfect super-insulated former for stone, concrete or brick and
block walls. Large amount of money? Well in the worst case scenario we
might have spent 25 percent of our budget before we realise it isn't going
to work. That still gives us 75 percent of our budget to rescue triumph
from disaster.

> Your lengthy discussion of techniques, plans, operations, risks and
> drawbacks show that you have given this a lot of thought.  However, I
> find many of the "facts" included in your presentation to be
> debatable, and a few to be wrong.
There were a lot of contentious and unproven statements in our
presentation. We should perhaps have qualified all these statements with
ifs and buts and maybes, but it was more fun not to.

> Obviously, the risks go up when an
> analysis is performed based on incorrect information.  The risks also
> go up with each untried element.  It is hubris to believe that we can
> anticipate all problems and design for them.  The greater the number
> of new ideas, the greater the risk.  This is inevitable and
> exponential.  The best we can do, with good planning, is to keep the
> exponent fairly low.  It is safer, and in my view, better, to
> decrease the number of new ideas in a structure, when one is betting
> people's lives.
What you say is true, we cannot anticipate all problems in the design so
perhaps it's better to have a Just Do It attitude and deal with the problems
as they arise.

> My biggest concern is safety.
Ours too

> You state that building at ground
> level is a safety advantage.  However, every bale will be laid with a
> multi-ton structure hanging in mid-air, right above where the workers
> are working.  This suspended structure will become increasingly
> heavy, tall, and unstable as building progresses.  I see this as a
> safety disadvantage.  In relation to jacking a building, you say:
> "Catastrophic failure is virtually unheard of."  You detail your
> plans for keeping people away from the structure during the jacking.
> I commend you on that, but I am frightened that the workers will then
> take up their stations, working next to and under this structure,
> after each jacking step is complete.
This is certainly a major concern. We are considering a jacking system
in preference to scaffolding primarily because we believe it to be safer.
We have wrestled with the problems of building a multi-storey straw
bale building in our climate ever since conceiving the notion of a
straw bale castle. We first considered scaffolding. Scaffolding would
be very expensive, because of our island location we would need to use
mainland scaffolding contractor. To provide adequate shelter from our
unpredictable weather, the scaffolding would need to be entirely
covered with tarpaulins. With the wind and rain we get, even in the
summer, these would catch the wind and might quickly be torn to shreds.
The potential for wind-induced scaffolding collapse would be
considerable. The unrendered straw bale walls would provide little in
the way of support for the scaffolding, so it would have to be free-
standing and, however well constructed, would sway alarmingly. I've
worked on two storey scaffolding which felt very unsafe; there's no way
I would ask volunteer wall-raisers to work on four storey scaffolding.
Wall raising would take longer as the bales and lime plaster would have
to be manhandled up the scaffolding. So, scaffolding would probably
provide inadequate shelter, be very expensive, be potentially dangerous
and significantly slower.

> I have heard of enough collapses of jacked and propped structures
> that I would choose a different description of their
> failure-frequency.
Just as I've heard enough about injuries and deaths of people working
above and below scaffolding. We need some facts about the relative
safety of the two systems. I'll try and find statistics or research on the

A rough estimate puts the total weight at 100 tons. Not something
you would want to come crashing down upon your head. We
are thinking in terms of making the shelter, around the base of the
tower, fairly substantial so that it is capable of withstanding a
wall collapse from above; a crumple zone, safety cage or somesuch.

> The biggest risk is not that the building will
> suddenly drop vertically, in column.  I worry that it may buckle,
> tilt, twist or rack, so that the walls do not remain in column.  Wind
> has tremendous force and leverage on a building, and during the
> construction phase, the building will not be tied to the foundation
> in the usual sense.  I hope you have plans for many struts, guy
> wires, braces and buttresses.  These will increase the safety during
> construction.
Very good point. We hadn't given much thought to the impact of the
wind on the building during construction, beyond thinking no work
would take place in windy conditions. Guys would certainly be a good
idea to restrict lateral movement.

> When the building is complete, and the braces removed,
> the integrity of a load-bearing strawbale building depends on the
> strength of the stressed-skin panel, with the render layer providing
> essential compression and tension functions.  I am skeptical,
> particularly during the long curing phase, that lime render can be
> relied on.  I would be skeptical of portland cement, too, lacking
> detailed modeling of the forces involved.
We will carry out some experiments to check this.

> I have questions on a few details, as well, but the above is probably
> more than enough for one message.
All comments and questions welcome.

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