Earth-sheltered greenhouse

Winter weather here in the north requires protected grow space.

By Dan Rubin

The basic principle is simple: if you live north of the 40th parallel, building a greenhouse with clear walls on all sides makes absolutely no sense. Since sunlight will never enter through the north side of the building, that side should be insulated rather than transparent, to retain heat.

This simple concept was brought home to me by Elke Dettmer, my nextdoor neighbour, here in the outport town of Pouch Cove, Newfoundland. Elke needed a greenhouse. She mentioned she was thinking of building one into the side of the hill, facing south toward the open Atlantic.

As soon as the earth sheltered concept crystallized in my mind, I began to wonder how it would work. What would it take to build one? How much would it cost to heat?

I just couldn’t shake the idea of the greenhouse “with its arse in the earth.”

Memorial University gets involved

When I met Marc Kielley, a project director at Memorial University, at a greenhouse conference in St. John’s, he suggested I should contact Andrew Fisher, vice-dean of engineering. Andy was able to offer the services of two co-op students to turn the basic idea into a design. So my quest continued.

Within a year, a third student had pitched in, and then we had the design down on paper: the Earth Sheltered Greenhouse would be a year-round grow space for vegetables, flowers and fruit.

Once we evaluated cost of construction materials and heating, we knew we had something special. For a 12-by-20-foot building, cost of materials was less than $10,000 and baseboard electrical heat would add less than $400 per year. So this was more than just a greenhouse; it was a game changer! The Earth Sheltered Greenhouse would allow people in a rural town to grow healthy food for their community at low cost.

When I brought this design to a meeting with the staff of the Memorial University Botanical Garden a year later, things began to move fast. I presented our plan hoping for some mild interest. But Kim Shipp, director of the Garden, was more than interested: she immediately committed to help build it. She also shared some sage advice: in order to get in line for funding from the university and make sure our design was solid, we would first apply for a start-up grant to thoroughly evaluate the design, by bringing together the best local stakeholders we could identify.

Farmers and food policy experts

So we convened a focus group made up of members of the local farming and food policy community: a bunch of hand-picked heavy hitters. With their help we plowed through a rigorous series of topics: structural design, team needed to operate the greenhouse, cost of inputs, crops and products to be produced and most importantly how to get the local community onboard and in support of the project.

I also wanted this group to examine policies at the provincial and municipal level that are keeping people from producing their own food. The consultation was amazing. We produced 270 recommendations for greenhouse design and operation! And then we were ready to build.

Once again, amazing luck and synchronicity were with us, because we found the perfect place for our demonstration greenhouse. In the middle of St. John’s, the last scrap of working farmland, the O’Brien Farm, was being turned into a training centre for education in sustainable agriculture, with the support of a high-powered non-profit board. In partnership with the O’Brien Farm Foundation and supported by a second round of funding from Memorial’s Office of Public Engagement, we are currently about halfway to completing the building.

We also founded a non-profit society to reach out across the province and connect community food producers. Food Producers Forum (www. foodproducersforum.com) has built a website with 170 pages of solid information about gardening, farming, fishing, hunting and foraging. We are weaving together a solid network to help rebuild provincial food security. About the greenhouse

So, what is an earth sheltered greenhouse, and how does it work?

The structure we are building is a 14-by-24-foot building with a concrete back wall, insulated by two inches of rigid foam and protected by concrete board, then buried in the hillside. The end walls are also earth insulated, but the front roof and wall are polycarbonate panels to let the sun in. The concrete acts as thermal mass, so even in winter, with day length shortened to only six hours and sun low in the sky, the interior can still be kept above 5 degrees Celcius, with little or no added heat.

The concrete foundation for the earth sheltered greenhouse.

Concrete walls for structural support and thermal mass topped by the lumber structure.

Don with the greenhouse.

David Goodyear’s finished four season greenhouse in Flatrock.

The Earth Sheltered Greenhouse Team, from left to right: Engineer Etienne Chaytor, Project Facilitator Dan Rubin, director of the MemorialUniversity Botanical Garden Kim Shipp, MUN Faculty of Medicine Dr.Atanu Sarkar and O’Brien Farm Manager Aaron Rodgers. be kept above 5degrees Celsius, with little or no added heat.

The building is a simple framed structure with a central ridge beam, supported by laminated posts.

The overall cost of building the larger building has now passed $20,000 but we have also received additional federal funding to allow us to equip our greenhouse with solar panels (for net metering), lighting, fans, an irrigation system and a complete digital monitoring and control system.

The well-insulated metal back roof will act as water catchment, with rainwater and snow collected in a gutter and funneled through a filter to fill one or more 1000-litre water tanks inside the building. In addition to providing added thermal mass, the water will be used for irrigation or it can be heated and circulated underground to warm the raised beds inside the greenhouse.

Dan’s home greenhouse, built against the side of a shed.

Other greenhouses in action

We know that this will work because we already have a working example in the nearby town of Flatrock, where Dan’s home greenhouse, built against the side of a shed. Early seed starting is a primary function of the greenhouse. David Jason Goodyear has had his Four Season Greenhouse up and running for two winters already.

Early seed starting is a primary function of the greenhouse.

David has found that with the low temperatures and gray skies of winter, enough sun energy enters the building that he has turned his electrical heaters off and can rely on an occasional boost from the GAHT (ground air heat transfer) system installed under his greenhouse. The GAHT system stores solar energy in the soil, to be retrieved when needed, rather than being lost from the building.

With this type of design, only a tiny bit of additional energy is needed to maintain growing conditions, even in the coldest months, here on the coast of Newfoundland. Further north or in the interior of Canada, where it can get a lot colder, you can apply the same principles, as demonstrated by Jianyi Dong, the immigrant farmer who is growing vegetables in Alberta using a passive solar design that he brought with him from China.

In David Goodyear’s structure here in Flatrock, he has grown four cycles of cold tolerant greens through the worst winter weather in memory, with a cost in electrical energy of $5 per month for lighting and air circulation. As the weather warms up, his building will transition to grow warmth-loving vegetables like tomatoes, cucumbers and peppers, as well as perennial fruits like strawberries, grapes and figs.

All across the north, people are experimenting with similar systems. A grower in Quebec is raising kiwis, apricots and table grapes in a converted barn turned into a greenhouse, using only passive solar heat. Designs developed in the Yukon also offer examples of what is possible.

Here in Newfoundland, the adventure continues as we prepare to reach out to seven rural communities to help them design and build their own Earth Sheltered Greenhouse. We know that by creating local food they can generate community health, pride and local economic opportunities.

We welcome interest from anyone across the country. We will be sharing details of our projects and progress on our website. We know that earth-sheltered is the way to go for year-round food production in our cold northern climate.

Dan Rubin is the owner/operator of Perfectly Perennial Herbs and Seeds, and Project Facilitator for the Earth Sheltered Greenhouse Project.

Dan’s home greenhouse grows cucumbers, peppers, tomatoes and basil.