Engineer Modernizes The Traditional Cruck Frame With Modern Framing and Straw Bale
Mixing The Best of Modern Materials With Traditional Form
It seems to me that we are the Kamikaze generation!
Our terrible legacy to our children is to be global warming because we are selfishly squandering most of the fossil fuels and polluting the damned planet in the process. I am appalled by our impact upon the worlds ecology and saddened by how much pollution is due to the energy demands of our inefficient homes.
| With ten of the warmest years on record being in the last twelve years it seems that we are blundering into an unsustainable ecological and energy future! The craziness is that it costs money to be a polluter. New UK homes use three and a half times the energy of German or Scandinavian homes and energy is and will be expensive – in many ways. |
Unfortunately the words “eco” & “green” have a hollow ring now they have been hi-jacked by politicians, nevertheless we will all have to think “green” if we are to create a more sustainable future for following generations.
It is difficult for individuals to have any effect but self-builders do have a chance to reduce their impact by careful choice of materials and services.
So I have this idea! – for a low cost, low energy, building with a minimal carbon footprint.
Brief C.V. I have, for forty years, earned my living from my (usually patented) engineering designs.
| I have built homes for myself and have done a lot of architectural design but I am not an architect. Over the years of building my own homes I have proved the financial and comfort benefits of investing in high quality building with, at the time, “over the top” insulation, and now we need to use more – much more. However most insulation has high “embodied energy” incurred from its production and distribution. |
Therefore it seems logical to use a natural material that is so abundant that it mostly goes to waste, that is local and reproduced annually yet is durable and cheap. That, of course, is straw.
| Why a house of straw? The UK alone produces 4 million tons of surplus straw every year – enough for 250,000 homes. Straw must have the lowest embodied energy of any building material and is probably the cheapest and most sustainable. Straw-bales have an insulation “U” value much better than required by the building regulations as well as excellent sound deadening properties which, together, give a living space an ambience that has to be experienced to be appreciated. |
Contrary to common perception straw-bales in a building, are not a fire risk, are not a vermin risk and are not short-term, but would compost back into the earth if and when required to do so. Straw in bales is so tightly bound that it doesn’t contain enough air to support combustion, just add a (carbon neutral) “breathing” lime render/plaster and any fire regulation requirement is easily met. There is no nutritional value in straw and so it does not attract vermin, it is only voids that vermin like, so proper attention to detail is the only precaution needed. Lime rendered straw-bales “breath” so evening out fluctuations of humidity thereby creating a healthier environment.
The problem is how straw homes are perceived.
Strawbale houses need to come out of the realm of committed radicals and into the mainstream of buyers if they are to contribute to more eco-friendly housing. This is in no way a detrimental comment on the pioneering hard work done by others in promoting the use of straw in building, just an attempt to move things on a notch.
| Because to an engineer, like myself, and all the homeowners, from whom I have canvassed opinions, most houses made of straw-bales seem to reinforce the children’s storybook illusion of straw houses being flimsy and vulnerable and therefore definitely not worth devoting ones working life paying for, with their resale value being the biggest worry. They have “the big bad wolf” syndrome, yet straw-bale homes in Nebraska USA are over 100 years old and still fit for purpose. |
My solution.
To try to overcome this reticence I have devised a more solid “engineered” design for a house that uses straw-bales as the main form of heat and sound insulation yet has a robust exterior that will cope with harsh weather and exposed locations. It is an attempt to overcome the “insubstantial” impression most straw houses give to the unconverted buyer. The quaintness of the usual straw house is indeed part of their charm to some, but my design is intended to give a more reassuring appearance, thereby extending the advantages of straw to a wider spectrum of buyers who find that roughness off-putting. After all, however much we all want to be ecologically sympathetic, in the end, we have to be convinced that our purchase is sound.
The design.
The design came from my experience of converting and living so comfortably for 20 years in a 15cty Kent barn.
The straw insulated house I propose will have the straw bale walls and roof as one.
The cross section is very similar to the medieval “cruck” frame in shape but made of deep curved composite wooden “I” beams, which serve as both rafters and studding, set onto a plinth wall of local materials. The straw bales will be sandwiched between these beams, which are like “ribs”, that continue for whatever length of building is required – at one bale spacing. Paired together like a bowed “A” frame they have the inherent strength of the “A” frame but contain more volume so will easily accommodate an upstairs for all or part of the length of the building. This gentle curved shape allows the straw bales to rise, seamlessly, all the way up to the ridge.
| The inside and outside is to be rendered with a “breathing“ lime plaster and, after allowing a ventilation space, the outside can be battened then tiled, shingled or even thatched according to local sympathies.
The whole structure is to be set on a low plinth wall of brick or stone. |
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This simple design is eminently suitable to being developed as a kit house, not just for homes but also as small workshops and art galleries – just add ridge glazing.
The design configuration is an elegant alternative to the conventional straw bale house because it avoids that awkward change of direction between vertical wall and horizontal ceiling which is a potential thermal and structural weak spot.
Although straw is capable of load bearing I have chosen this unusual wood frame configuration to give the building a more substantial structure.
This is intended to help overcome the resistance that most home owners have to the “organic” appearance of straw houses whilst giving a spectacular interior that leaves the owner an uncluttered vaulted space in which to do their own thing. It can be any length – a building in it’s own right with or without a first floor for all or part of its length, an extension or wing of a larger build by being abutted to another structure etc. It could also be built in stages as the family or its finances grow.
Also an aim of this design is to tackle the moisture levels within the bales in the UK climate (particularly here in Cumbria). Most strawbalehouses rely on large eaves overhangs to protect the walls but my idea is exploit the natural chimney effect, created by different pressures at different heights, to draw air under the tiles and over the exterior of the bales. Any solar gain on the tiles should further amplify this effect.
However straw is not the complete answer for a low energy building.
For a home I would try to add an ICF earth-sheltered basement/garage/utility, with some high-density thermal mass to help stabilise the indoor climate. This mass would be orientated to get the maximum winter solar gain, yet very little in summer. (ICF = Insulated Concrete Formwork, also proposed to be used in the plinth wall.)
Solar hot water, of course, and a ground source heat pump [GSHP] coupled to underfloor heating that, hopefully, could be run on electricity from renewable sources such as photovoltaic cells when they become more viable.
Add to this serious rainwater harvesting for loo flushing and the washing machine.
For rural homes, only a small area of land is enough to be self-sufficient in (carbon neutral) wood to fuel a room sealed woodstove as a homely supplement to GSHP. (Get energy from junk mail)
| Heat recovery and ventilation units (HRVU) are very efficient and will become widespread under the new regulations on air change in living spaces. However I am not sure of the wisdom of sealing buildings, I prefer natural materials that breath, most modern paints don’t and they give off VOC’s, as do fitted carpets and they also harbour mites.
The rise of asthma is not unconnected but a tip for Asthma sufferers; central vacuuming is a great help. |
Dust is removed from the house instead of being filtered into smaller more irritating particles and redeployed!
Conclusion
In response to our global predicament my individual contribution, for what it’s worth, is this proposal for an eco-friendly, energy efficient, simple, low cost building that uses, as the main form of insulation, a cheap and readily available material that is sustainable, local and a cheap by-product of food production.
The building can be an expandable self-build home, studio, workshop or art gallery. However the design is limited to the configuration described, albeit with numerous variations, so does not pretend to be the all singing all dancing answer on how to use strawbales, but I hope it will make the use of strawbales more appealing to a wider market thereby reducing our use of fossil fuels and lessen our increasing dependence upon foreign supplies.
The design was registered in June 2007, planning was refused in August 2007
Because of “alien” materials and “Cumbria is not the place for innovation”.
I appealed at the end of August and fortunately the inspectorate allowed my
appeal so granting me permission to build the prototype. Work will start as soon
as the Cumbrian weather allows. (February 2008)
Strawbalehouse progress (or rather lack of it ) January 2009:
After winning my planning appeal I looked for a manufacturer of the curved beams – to no avail so I proceeded to make them myself. Without investing in pneumatic jigs this was a labour intensive procedure but no real problems. At the same time I decided to give my local building control a go despite their reputation as being stuck in the 19th century – BIG mistake because they raised so many objections and refused to allow me to start even the footings until they were satisfied with every detail (even what trap I intended to use on the workshop sink and how I would do the scaffolding!).
But they smiled all the time at this Southern twit!
It slowly became obvious that they were determined to prove their colleagues in planning right who had told me “Cumbria is not the place for innovation”. They would not contemplate any figures or tests that are accepted by other councils. These delays caused me to miss last season. However, I have now found an independent building control officer willing to take me on – the only snag is that he is 80 miles away. My next problem is finance inasmuch as I am funding this prototype from my pension and savings income, which has more than halved in the past few months. Also my wife and I retired to this area to look after her 90 year old mother who sadly died this month so should we cut our losses and go to a more amenable (planning wise) area?? I must say the council’s attitude is in stark contrast to the people in Cumbria who have welcomed us unreservedly with absolutely no objections to my strawbale studio (or indeed an ICF polystyrene tower extension to my grotty (Technical term) 1975 house. But that’s another story).
Bureaucracy really is the enemy of progress and as George Bernard Shaw said “The reasonable man adapts himself to the world whilst the unreasonable one persists in trying to adapt the world to himself. therefore all progress depends upon the unreasonable man”. So we need a few more unreasonable men and women because things will always alter for the worse spontaneously if they are not altered for the better by design.
November 2009
Despite the financial situation earlier this year my wife Jo and I took the decision to proceed with the building of the prototype strawbalehouse so as to be ready in time for the harvest. The base and plinth walls were completed and the frame was raised by the time the strawbales arrived in late October; however the weather immediately worsened with the result that, everyone has seen on the news, our local town of Cockermouth was devastated by floods after the highest ever recorded rainfall – just the time to build a strawbalehouse!
I had intended to fit the bales from the outside but I have had to temporarily cover the frame with tarpaulin and batten down for the winter so I will now install them from the inside.
The lime man says he needs three weeks frost free to spray the lime (I have too much arthritis to contemplate hand troweling) so it looks like it will be the spring before the finishing can be started.
LESSON 1: Get the bales the year before you intend building, have good dry storage and start in the spring.
Because of the obstructive attitude of my local building control I have had to engage an independent company, JHAi from Dorset – only 350 miles away. However with their help I will go for “type approval” so that any future builds will only need to cover site specific issues with BC.
So far I have needed assistance only for tamping the concrete slab. (The concrete is there so that the building is not only “fit for purpose” but so it will last long enough to dilute its carbon footprint down to negligible).
The “ribs” were raised easily with just a hand winch and then shuffled along to one metre spacing (see photos below), the stainless steel cross wires were then fixed to provide longtitudinal rigidity.
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Engineer Modernizes The Traditional Cruck Frame With Modern Framing and Straw Bale
