sunken Greenhouse
Wallipini
Located Central IL, northern end of zone 5b. It’s 60 feet long and 9 feet from front to back wall. Depth of the cold sink is 8 feet below grade and the grow bed is 3 feet below grade. Each front panel is 6' tall by 4' wide. ( The cold sink was dug 8 feet below ground and the grow bed 4 feet below.)
The walkway is 4 feet wide, so we can comfortable fit a wheelbarrow down it, and the growbed is 5 feet wide, which accommodates about 2 feet of barrel diameter and 3 feet of grow space. The total width of the structure is 9 feet.
- Construction
- Followup Video
- Russ Finch "Man grows oranges in Nebraska in the winter" "Kirsten Dirksen 'Nebraska retiree uses Earth's heat to grow oranges in snow'"
- Mike Oehler design based on Mike Oehler's "Earth Sheltered Solar Greenhouse" ideas
- "Geoff Lawton PRI Invermere British Columbia Geo Solar Greenhouse" for an interesting discussion on Earth batteries.
I thought you might be interested that your greenhouse concept was popular in northwest Minnesota in the 1970s-80s. It was called the Brace greenhouse design from Canada. There was research at Michigan State University, Penn State and Rodale Press on the design. Detroit Lakes Vocational Institute in Minnesota offered on-site instruction to growers and a correspondence course for solar greenhouse and greenhouse vegetable culture. Rodale Press published several books on the concept. Organic Gardening Magazine, September, 1982, had a cover story on solar greenhouse food production.
Costs
It cost us less than $5000. We recycled a lot of material and the build was quick. Cost really varies with how you source your materials. In our case most of the lumber was rough cut, from our own woods, on our personal Lumbermill. The barrels were sourced used for $5 each. The topsoil was left over from a friend, so our main expense was the twin wall poly carbonate glazing, which ran us around $2600. We also had to pay to dig the trench, but we packaged that in with other excavation work we were doing at the time. So it probably cost us around $800 or so. Then there was hardware and just some miscellaneous items. I think our grand total actually spent was around $4000. If we had had to buy all the lumber, it would’ve been at least twice that.
Now that I know it works and more than pays for itself, I would actually invest more. Additions would be a footer for the tanks, a cement front wall, and a subterranean air flow section to utilize more ground temperature stabilization. I think a combination of this and Rush Finch's design (Greenhouse in the Snow) would be ideal.
I’m guessing we spent around 100 man hours to complete to the point being operational.
However, I didn’t do a great job maximizing grow space and I’m now using more vertical space. Be sure to check out Russ Finch also. I was just introduced to his work recently and I’m very impressed.
What would you change?
A Different Way 11 months ago First, a really well reinforced front wall. We knew when we started this project, that we would eventually wish we had done that, but we intentionally built this as kind of a prototype and cut cost in that area. Another thing we would do is add far more ventilation pipes underneath the grow bed to circulate air better. We don’t have good enough airflow in the heat of summer to cool it. We would also invest in better topsoil for the garden. We got what we were told was topsoil but wound up being black clay that has been a curse ever since. Finally, we would put an actual footer under all the barrels, as we have issues with them settling and tilting, and we have to reset A couple each year.
I wondered if another eaves trough along the south side would have kept the water from draining down the panels and making the dirt in front collapse. Also, is the size of the walkway imperative? Could it be built to accommodate a wheelchair’s width and height for a seated person to work in the beds?
A Different Way Because the roof is angled to the back, water does not spill off the front. Our particular issue is the fact it is located only about 8 feet from our driveway, which is consistent pressure, and the 8 feet in between is heavy clay soils that become water-logged at times. As stated, we knew this would eventually be an issue, but our goal was to build a prototype that would last about 10 years. The walkway could easily be made to suit a wheelchair. Just be aware that the wider it is, the more the square footage increases, and that in turn increases the air space that must be heated and cooled. Depending on your zone, this could be used to your benefit, or could require a little creativity! You could decrease the height of the grow bed by raising the level of the board path, but still allow for a good cold sink and good air flow.
Thermal Capacity
On average, the walipini remains about 30 degrees above outside temperatures, however it varies. We have a lot of cloudy days during winter, and go weeks at a time with no sun to really heat it. Temps can get a bit lower during those times. On nice sunny days, it can get up to 50 degrees warmer. In the last three years, I think the lowest temperature we got was at the end of a spell of cloudy days, our water in the barrels had run a bit low so they weren’t providing much heat at the time, and the temperature dropped to 26°F one night. It was about -6 outside.
Ontario? I think it could work up there. However, you better seal every nook and cranny and try to draw air in through the ground. -25 is pretty bitter cold even with 1600 gallons of water. I’ve hit -17 F and avoided freeze.