A 500-year, Net-zero, Cob Solar House for Half the Cost of Conventional Construction

In a previous article, I discussed how to get a 1,000-year, carbon-absorbing, FREE house. (The free part involved trading your labour for the materials to build the house.) In my area there is a 500-year, net-zero house that last year sold energy to the grid. It was far from free, but then that was not the owner-builder’s intent. It is worth a closer look to see how they did it.

Ann and Gord Baird took 20 months off work to build a house for themselves (including two children) and Ann’s parents. The result is

North America’s FIRST code-approved seismically engineered load bearing insulated cob house featuring: solar PV and wind power, grid intertie, solar thermal heating, rainwater harvesting from a living roof, composting toilet, grey water re-use, and passive solar design.

The house includes a suite for the parents, and the total size including the suite is 2,150 square feet. It has 5 bedrooms, 2 bathrooms, and 2 kitchens. They supplied 315.14 kW-hours to the grid last year from a 2kW solar array while powering “two fridges, one freezer, a hydronics system, wood working shop, all our irrigating pumps for our food gardens, two kitchens, and 6 people.” Not bad.

Even without the (very expensive) solar array, their energy usage was 2105 kW-hours, which would have cost approximately $200 had they been purchasing power from BC Hydro. For comparison, when I had an electrically-heated 1,100-square foot condo I paid ~$125/month, and when I had a detached, electrically-heated 1,600 square-foot house with airtight wood stove assist, I paid ~$175/month. The Bairds would have paid $200/year. Check out Gord’s detailed breakdown and very interesting Conversation on Conservation.

Clearly the Bairds are in very good position come peak oil. Other advantages include a house that will last at least 500 years, is virtually fireproof, had a minimal carbon footprint to construct, and much more.

But what was the cost? Well, hefty – at first glance. But some things to keep in mind:

• This was the first such house built in the area. Everything being done was new to the builders (the Bairds), the various building inspectors, and the structural engineer they had to hire
• Minimum upfront cost was not the primary goal. Energy independence, a beautiful house, and doing things right were. I visited the home twice while under construction and was impressed with the Baird’s attention to detail in every aspect, as one of their goals was to set themselves up for future building/consulting work.
• The solar electrical and heating/hot water systems were very expensive.

The same house could be built for less now, given what the Bairds learned. A similar house could be built for much less if some compromises were made on the energy front. The Bairds’ house has radiant heat in the floors and even in the built-in cob living room seating. If instead passive solar and a solar greenhouse, supplemented by a masonry stove or woodburning fireplace was used, this would cut ~$70,000 from the cost. Of course, then you need wood and a lot that supports solar gain. And some active solar would still be required to provide hot water.

The house is wired for AC and DC; choosing one only would cut the cost, but if I recall correctly they had to have AC according to the building code. The building code also increased costs in other ways; the Bairds’ are quite happy with their bucket-and-chuck-it toilet, but the building code specifies at least one working flush toilet must be installed in every residence. The Bairds plumbed this toilet in, demonstrated to the plumbing inspector that it worked, and then immediately removed it.

(As an aside, the bucket-and-chuck-it system works as follows. The ‘toilet’ consists of a box with a toilet seat. Inside the box is a bucket. A small computer-type fan evacuates the box, so it is virtually impossible for odours to escape into the bathroom. Once one does one’s business, one sprinkles some wood shavings into the bucket. I personally checked out the outhouse version shown in the link and there was no odour despite the 4 adults, 2 children, and guests who used it. The interior bathrooms were not yet complete. The compost heap which received the “humanure” also had no odour. The Bairds’ based their system on The Humanure Handbook: A Guide to Composting Human Manure by Joseph Jenkins.)

The other major expense was their own labour, which they costed out at $101,600. During my visits, the Bairds said they were also accounting for all volunteer labour. Delete their labour and the solar/radiant heat systems, and the total cost is ~$200,000 plus land. That includes nearly $15,000 for appliances. For Victoria, where building costs run ~$200 per square foot (plus land), that is very inexpensive. Their house alone would have cost $430,000, not including the irrigation and other systems they installed. Their house is also finished to a very high standard, with liberal use of (mostly reclaimed) wood for custom kitchen cabinets and walls.

In the end, the Bairds have a beautiful, solid, energy and largely water-independent house that sells electricity for less than half the cost of conventional construction. That’s damn good.

UPDATE: I asked the owner-builders for feedback and corrections on the article, and they pointed out three things:

• The total cost to build including labour (but not land) is $148 per square foot
• “We are pre-wired for wind… but have not yet been happy with the technology… though possibly this year we may invest in a vertical turbine, though with our consumption numbers we really don’t require excess generation (much to our surprise)”
• “With the composting toilet… cedar is the only wood chip media we don’t use as it is antibacterial… fir, elm, hemlock, pine… all good.”

Resources in this post

• The Bairds’ Flickr photos, with great pictures from all stages of construction from experimentation to finished house.
• The Bairds’ website and blog are well-worth reading.
• If in the area or in the market, by all means take a tour or a course, or use their consulting services; I’m sure they will save  you much more than the cost. (I do not receive any commission.)