[Strawbale] Load Bearing Multi-storey Straw Bale Tower House Castle

Luk Jonckheere l.jonckheere at pi...
Fri Aug 1 11:02:42 CEST 2003

I don't know anything about building techniques. But crazy ideas about straw
bale castles stimulate my imagination.
In a situation where every kilogram counts, it could be good to reduce the
weight of the plaster. I heard about buildings where the foundation was made
of foam-concrete. Is there any such thing as foam-plaster and could it be
useful in this strawbale-castle?
If this is just a stupid idea, forget about my e-mail.
Wish you succes, kind regards,
Luk Jonckheere

----- Original Message -----
From: "Chris Mowatt" <ChrisMowatt at i12...>
To: <strawbale at amper....muni.cz>
Sent: Monday, July 28, 2003 12:49 PM
Subject: [Strawbale] Load Bearing Multi-storey Straw Bale Tower House Castle

> Four Storey Straw Bale Tower House Castle at The Free Energy Centre,
> Kildonan Farm, Isle of Arran, Scotland
> Has anyone any experience of building multi storey straw bale buildings?
> We want to build a four-storey tower house castle. This would be in the
> style of the traditional Scottish four storey tower house castle. It would
> be about twenty metres in height and include a conventional pitched roof
> simulated battlements. The aim is to use load bearing straw bale
> construction methods. We have spoken to the local authority planning
> department and building control and their response was encouraging.
> This idea presents many challenges. There are very few two storey straw
> houses and, so far as I know, no four storey buildings. Our site at
> Farm is a very exposed location subject to strong winds, heavy rain and
> extremely variable and unpredictable weather! Not the ideal place for
> construction of a straw bale building! However, challenges are what makes
> life interesting and to succeed would be very noteworthy.
> Our thoughts are to build everything at ground level and raise the
> sections on jacks and using the weight of the completed structure to
> compress the straw bale walls during construction. The build would take
> place in something like the following sequence:
>     1. Construct the roof and fourth storey wallplate at ground level
>     2. Position Jacks and jacking props to lift from wallplate jacking
> points
>     3. Lift building 375mm, i.e. one straw bale course (350mm) plus some
> clearance
>     4. Prop building from wallplate propping points
>     5. Relieve pressure on jack (but not release entirely - so the jacks
> act as a fail safe should the props fail)
>     6. Lay one course of bales
>     7. Repressurise the jacks
>     8. Lower props 50mm
>     9. Lower building until the load is resting on the bale wall and
> compressing the wall
>   10. Lift building back up to 375mm mark
>   11. Raise props
>   12. Release jacks so props are taking the full weight
>   13. Reposition the jacking props (i.e. increasing length by 350mm)
>   14. Repeat operations 3 to 13 until ten courses (i.e. one storey has
> completed)
>   15. Lime render and lime wash completed storey
>   16. Assemble integrated wallplate, floor joist matrix and flooring for
> next storey
>   17. Repeat operations 2 to 16 until final storey (ground floor) walls
> complete
>   18. Remove jacking system
> There are a number of advantages in this approach
>     1. Construction can take place in safety and comfort close to ground
> level.
>     2. There will be no need for scaffolding.
>     3. The weight of the raised structure can be used to compress and
> stabilise the straw bales of the storey under construction during wall
> raising and during rendering.
>     4. There will be no need for a wire or thread type tensioning system
> compress and stabilise the walls.
>     5. Only the storey being worked upon needs to be protected from the
> weather.
>     6. The straw bale walls will be protected from the weather by the roof
> structure from outset.
>     7. It will be spectacular if successful.
> The disadvantages are
>     1. Expense of a specialist high precision jacking system (20000 GBP,
> 28000 Euro,  30000USD, 45000 CAD) for a one-off lift.
>     2. Potential danger of partial or complete collapse during the jacking
> operation.
>     3. Untried on straw bale building.
>     4. Need for strong jacking points and good load spreading from these
> jacking points.
>     5. It could be spectacular if it fails.
> We plan to address these disadvantages in the following way.
>     1a. We are investigating the design of a lifting system using cheap
> produced components. The inherent flexibility and relative lightness of a
> straw bale building means that a specialist high precision lifting system
> may be unnecessarily precise. Moreover, one of the beauties of building
> straw bales is the simplicity of construction. We do not want to use
> sophisticated high precision high cost tools if at all possible. We want
> solution to be suitable for use throughout the world. It should be
> to make the jacking procedure simple, safe and accurate.
>     1b. It may be possible to recoup some of the cost by selling the
> equipment after use.
>     2a. The jacking system will be remotely operated and people will be
> excluded from the building zone during the lift and anytime the jacks are
> under pressure.
>     2b. There will be multiple jacking points (sixteen or more) will be
> to maximise load spread and minimise the impact of the failure of one
> of equipment.
>     2c. All jacks will be independent of each other, so no one piece of
> equipment will be critical to the lift.
>     2d. A fail safe will be built into the system to ensure the maximum
> in the case of failure is 50mm (2 inches).
>     2e. Pressure to each jack will be manually controlled, but using
> synchronised pumping. Observers using binoculars to monitor progress
> measuring sticks will ensure the lift progresses smoothly and evenly.
> Observers will relay instructions to the people operating control valves
> using mobile site radios (walkie talkies).
>     3. Jacking buildings is common place for underpinning operations and
> many large buildings are routinely jacked during construction. The
> lightness and flexibility of straw bale buildings make them ideal for
> lifting.
>     4. The intention is to build an integrated wall plate and floor
> structure with extended timber I beams to provide external jacking points
> (to be subsequently removed). This structure will be designed to spread
> load and provide sufficient strength for the jacking points.
>     5. Failure will be a learning experience. No publicity is bad
> Jacking operations are, although exciting in concept, unexciting in
> practice. The lift takes place very slowly under controlled circumstances.
> Catastrophic failure is virtually unheard of. Any failure would be
> and small scale. Such failure may lead to the project being abandoned if a
> problem cannot be resolved, but it is unlikely to lead to front page
> es.
> We are also considering laying the straw bales on their sides, rather than
> in the conventional way. There seem to be some a number of advantages of
> doing this.
>     1. The compressive and shear strength of the straw bale, when part of
> stressed skin sandwich, i.e. when rendered with lime render, is stronger
> when the straw are in vertical alignment (the way nature intended). This
> advantage is contrary to the findings of some early research on the
> but that research was on the straw bales themselves not the stressed skin
> (rendered) straw bale sandwich.
>     2. The walls are thinner giving greater internal floor space.
>     3. The insulation properties of the straw bale are improved (contrary
> what one would expect).
>     4. The straw bale is less permeable to moisture in the same way a
> is not very permeable to moisture.
>     5. There aren't thousands of straw ends sticking out into the render
> stucco to invite moisture in by capilliary action.
>     6. The intercourse bonding may be improved by allowing straws from
> neigbouring courses to interleave with each other when compressed.
>     7. Fewer straw bales are required giving a small cost saving.
>     8. Fewer straw bales are required giving a reduction in wall weight.
> Points 2 and 6 may also contribute to the disadvantages:
>     1. A thinner wall concentrates the weight on a smaller area requiring
> stronger foundations.  The effect of this is reduced because the weight of
> the straw bales is lower owing to there being fewer of them. However,
> a fair proportion of the weight of a straw bale building is made up of
> wall plates, joist timbers etc this unaltered weight would still be
> on a smaller area of foundations.
>     2. Interleaving of straw stems when under compression may cause
> and may even result in the strings or bindings failing.
>     3. Lime render (the most suitable form of weather protection for our
> and windy climate) will not adhere as well to vertically aligned straw.
>     4. There is not much research, practical experience or knowledge on
> building in this way.
> We feel the disadvantages can be addressed in the following ways.
>     1. Stronger foundations. We intend to use self-draining stone
> foundations up to a height of 500mm above ground level (to minimise splash
> damage to straw bales). These will be tapered to increase the area of
> upon which the weight is bearing.
>     2. We will experiment with the behaviour of straw bales under
> compression and decide whether the bindings need to be suplemented.
>     3. We will experiment with spray methods of applying the lime render
> using different consistencies of render applied in different thicknesses
> see if the render can be driven into the straw to provide a deeper bed of
> adhesion. If this is unsuccessful we will try using modern bonding agents
> such as PVA and SBR to improve adhesion.
>     4. We are searching for any knowledge or exerience on the subject.
> We hope to be able to show that tall buildings can be built swiftly,
> and economically using load bearing straw bale construction methods.
> We would be grateful for any advice or information anyone can offer.
> Kind Regards
> Beth and Chris Mowatt
> Kildonan House
> Kildonan
> Isle of Arran
> KA27 8SD
> Scotland, UK
> Tel. +44 1770 820 324
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