The Rubble-Trench Foundation

Rubble-trench foundations were used extensively by architect Frank Lloyd Wright in the first half of the 20th century. They have fallen out of favor as concrete has become the norm and many code inspectors are unfamiliar with them. After finally deciding that a concrete slab was unacceptable to us in terms of meeting our project goals (because of extremely high embodied energy, high cost---and hard on feet and legs!), we decided that a rubble trench was time-tested and would provide a fairly simple, low-cost, environmentally friendly alternative. We also decided, after much deliberation, to use wooden grade beams (rot-resistant hemlock) on top of the trench, rather than concrete grade beams. We are betting the long-term soundness of these wooden grade beams on the steps we have taken to ensure that very little water ever touches the beams, that any moisture that comes in contact with them immediately drains away, and that, if for some strange reason water finds its way into the trench, it will not freeze before it drains away. A number of people have tried to persuade us to place a moisture barrier under the hemlock grade beams, but we feel that such a barrier would only serve to trap any moisture that found its way to the beams rather than allowing it to drain away. The following features of the foundation and house should keep the grade beams dry and sound:
> appropriately constructed trench dug all the way to ledge, with raised berm of washed stone and good bottom-of-the-trench drainage
> ground sloped away from the outside of the trench/house
> blueboard insulation angled over outside of trench and backfilled with washed stone
> a 2.5' roof overhang to keep water off the walls and grade beam
> a berm and a swale on the upslope side of the house to direct water away from house
(Excavating and filling the trench, and the graywater septic, is the only part of the construction for which we hired a professional contractor.)

Plan finalized

Our final plan is for a 43' X 25' (40' X 22' interior dimensions), rectilinear house. This is 880 square feet. Take away 176 sq ft for the shop and cold storage, and that leaves 704 sq ft of living space. Modest by today's standards: some would even say that dreaded word, "small" (people who have perhaps never heard of the Small House Society or read The Not So Big House). The skeleton is post and beam (using the methods outlined in Rob Roy's Timber Framing for the Rest of Us), which we will fill in with 18" cordwood infilling. Here is the final model for the post and beam framework. The high side faces south and will hold most of the glazing, and most of the living space. A central cordwood wall will provide thermal mass for the solar radiation thus gained. The low/north side is where the bedrooms and cool storage will be located.

House plan

Rob Roy's arguments about the maximum area of round structures make a lot of sense, and so our first house plan was round. Our second was 16-sided. After receiving foundation bids that nearly equaled our entire building budget, and realizing that a sixteen-sided roof would cost even more, we started over, working from these criteria:
> Simple enough for novices to build
> Passive solar
> Can incorporate standard-sized building materials
> Cheap enough to pay as we go
Most importantly, we reminded ourselves, the house is a means to an end---a different lifestyle---the house isn't the point. It's just a way to come up with a home that's easy/cheap to heat and power, is fairly "green" to build and healthful to live in, and easy/cheap enough to build to avoid debt.
The design elements flowed clearly and easily from these criteria. Our desire to take advantage of the sun and be able to use "off the shelf" building material meant that the house would have to be rectilinear. In order to be simple and cheap, it would also have to be single story. We decided upon a shed roof, since this is the simplest roof to build and lends itself to capturing southern sun. (Passive solar also meant that we couldn't tuck the house under the edge of the woods.) Here are our initial sketches for the resulting plans:

The back story

The influences leading to this building project have been many and varied, coming from our diverse backgrounds: Extension work, back-woods businesses, building boats, gardening, metal working, studying and reenacting history, reading Jack Henstridge and Rob Roy, years of MOFGA's Common Ground Fair, reading James Howard Kunstler , Barbara Kingsolver, and Michael Pollan . . . experiences that, over time, inexorably pointed us in a certain direction. Our growing awareness of the increasing global demands for limited resources such as oil, water, and food finally moved us from thinking to planning. After a long search, we found a piece of land big enough to farm, small enough to pay for, in a community with like-minded people.
One challenge was to figure out how to cut our expenses enough to change our lifestyle (or is it the other way around?)—keeping in mind that one of our four children still needs to be put through college. So we began the process of eliminating debt. If all goes well, we will end up without a mortgage.
The process of self-education has been a fascinating journey. We read a lot of books on alternative building and attended Rob and Jaki Roy's Earthwood building school. A deed restriction prevents us from tying into the electric grid, so we are learning about solar electric and gravity-fed water systems. In researching options for septic systems we stumbled upon Joe Jenkins' brilliant Humanure Handbook. In our search for an environmentally friendly house foundation, we discovered Frank Lloyd Wright's rubble trench concept. We will talk more about all of this later, but right now we have just broken ground and are VERY BUSY!!!