Engineer Modernizes The Traditional Cruck Frame With Modern Framing and Straw Bale
There are so many advantages to straw bale construction. Engineer Brian Waite lists some of them from his home in Cumbria:
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.
He has designed a straw bale home that adds the additional advantage of some very clever engineering. Most strawbale buildings have straw walls and use other materials for the roof; Waite essentially eliminates the roof (or the walls, depending on your perspective) and creates a cruck frame, a modified A frame that is curved to maximize interior volume.
Glenbuchat Heritage Archive/Public Domain
In traditional cruck framing, the curved pieces carried the load, while non-structural walls and roofs were added on top. It fell out of favour because it used a lot of long pieces of wood that the navy wanted, and because builders learned that the walls and the roofs could be designed to carry the loads without the crucks.
Waite cleverly manufactures his crucks like composite I beams, and fills the space between them with straw bales from sill to roof, with no discontinuities.
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.
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.
While the configuration here is fairly traditional in appearance, it doesn't have to be. Brian Waites writes:
By using an "A" frame (albeit slightly bowed to give a more viable first floor) the structure is both simple and strong with the added advantage of an interior free of structural requirements that can be divided as the owner wishes - with or without a first floor.
The designer concludes:
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....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.
More at Straw Bale House