Q: We are planning to build a cordwood heated greenhouse and art studio. The size is will be about 16 X 16 feet interior with 16-inch thick walls. We are looking for a cost effective green solution for the foundation. Two options seem to be not only cost effective and environmentally friendly but also do not require skilled labor. The first is a rubble trench foundation and the second a rubber tyre footing. Which of the two is most suited to cold climates? Our frost levels can be as much as 3 feet deep.

Here is a link to a page with some information on the two type of foundation: http://www.earthgarden.com.au/strawbale/footings.html

Was going to limit myself to one question but I can’t resist. We live in Ottawa Canada close to the Ottawa Valley where cordwood building has survived for many years. When those building were erected (some over 100 years ago) what type of foundation did they use?

A: First, the foundation question. Thank you for the link in your letter, which I followed and found to be quite informative. My personal comments are: The rubble trench is a good low-cost foundation method that works extremely well as long as you provide a positive drainage with - for example - a 4" perforated drain pipe near the bottom of the trench, drained positively to some point above grade, as they say "to daylight." The trench needs to be at least as deep as the worst anticipated frost depth in your area, and the slope of the site needs to be sufficient to accommodate drainage as described above. Other readers: if you are unfamiliar with the rubble trench, follow the link in Daniel's question for a preliminary overview. The best discussion I have seen on this method appeared in Fine Homebuilding Magazine (Issue 18, December, 1983, pages 66-68), and can be found in their (unfortunately) out-of-print anthology called The Best of Fine Homebuilding: Foundations and Concrete Work, at page 40. The ISBN # is 1-56158-330-8. This is important because Fine Homebuilding has recently published another book with almost the identical title (and different ISBN number) which does not include the Rubble Trench information. This article is very well detailed and illustrated and is good enough to build from, as my neighbor did for his strawbale home.       

As for the tire foundation, I have no personal experience. The Earthships seem to do well when built in the appropriate climate. I am unclear as to what is so environmentally sound about burying tires in the ground. On the other hand, I don't claim to know any other good way to get rid of them.     

Second question, about foundations for old cordwood buildings, called "stackwall" in Canada. The ones I have seen (in your Ottawa Valley neighborhood, by the way) have been on stone foundations, both drystone and with mortar. Again, take the foundation down to local frost code numbers.

Q: Could cement blocks be used for the foundation under the cord wood, or is a foundation needed under the wood?

A: A concrete block foundation under the cordwood is acceptable, as long as you attend to frost depth considerations in your area.

Q: I was thinking of building a cordwood home. I currently have sauna tubes in the ground and was going to put a floor on top and build a stick house. Can I go up with cordwood construction or do you think the weight would be too much?

A: Several people have built cordwood on posts or pillars, but they have to be fairly close together and joined by a heavy plate beam around the perimeter of the building. Posts are typically six feet on center in this case. You do not specify your sona tube spacing.