Natural Building Techniques: Timber and Recycled Light-Framing
This main structural system of this home addition is heavy timbers of Wisconsin White Pine. This type of framing is beautiful and durable, and has relatively low embodied energy, as heavy timber is not kiln-dried. About 40% of the light framing and the site-built roof trusses is wood recycled from curbsides in Madison.
There are numerous good references for learning timber framing, notably Ted Benson's books.
Above: Preparing to raise the frame.
Above: The moment of raising.
Above: Setting the trusses.
Students came from many states for the week-long workshops, some to learn to build their own homes, others to take back the techniques to their home communities.
Engineering our own trusses allowed us to use recycled and lower-grade wood, something a truss manufacturer would be unlikely to do because of liability concerns. We feel that the glued plywood gusset plates will outlast conventional metal gang-nailed truss plates, as the latter may in time rust. The pitch of the trusses is designed for the installation of solar collectors for domestic water heating.
Above: Site-built plywood gusset roof trusses.
Above: Larsen-type trusses at existing roof, where working space is limited.
Above: Straw-clay used with (mostly) conventional light framing.
Designing for straw-clay walls takes an understanding of the installation process. It's easiest and most successful to place and compact the straw-clay from above, so low-headroom situations require a different approach. Where we had an existing roof to work under we used Larsen trusses (a ladder-like stud made from two 2x2's and some scraps of plywood). Low-toxin fiberboard sheathing was placed on the interior and exterior faces, and the straw-clay was placed as "loose-pack", that is, less densely compacted. The earth plaster is anchored using furring strips over the fiberboard, in the traditional fashion.
The blind-framing (attached to the timber frame -- see the cross section drawing) functions to anchor and brace the massive straw-clay walls against side pressure (wind loads, seismic loads etc.). Bamboo or dowels are threaded through holes in the framing every 16" or 24" (40cm to 60cm) and are thereby embedded in the compacted straw-clay as it fills the wall form. Essentially, this is a latter-day "wattle" (the framing and the dowels) and "daub" (the compacted straw-clay mix) building technique that meets modern energy and structural standards.Conventional framing can also be used with straw-clay.
The picture above, on the lower right, shows a different addition framed with 2x6 studs by professional carpenters, with slight modifications to the plate installation to facilitate placing the straw-clay. Our current straw-clay homes use this framing system.
Old-growth Douglas-Fir, scavenged from curbsides.
We collected and planed enough in a two-week period for wood ceilings.