How We Designed Our Solar Greenhouse

by Rob Avis

We live and garden on an urban lot in Calgary, Canada, located on the 51st parallel north and approximately 80 km east of the front ranges of the Canadian Rockies. This northern climate presents many design challenges, including less than one hundred frost-free days, an annual mean temperature of 4.1 degrees Celsius and summer cyclonic weather patterns (i.e. high risk of hail). We are also considered to be a moderate temperate desert as our precipitation is around 500mm including snow. However, one of the advantages of growing food up north is the long summer days. There is no better place to observe this than in Alaska which also has an average of 100 frost free days but is renown for growing the largest vegetables in the world. Also, despite being cold in the winter, it is rarely overcast and we enjoy mostly sunny days. These two factors combined result in Calgary having nearly the same solar potential as Florida.

Traditional European Greenhouse

Passive Solar Greenhouse

In good ol’ permaculture fashion, we set out to enhance sectors and conditions that would improve our growing season (sunlight, heat) while minimizing those that we considered detrimental (cold, hail, frost). We quickly determined that a passive solar greenhouse was just what we needed and we set out to design one for our backyard.

There are two major considerations when designing a greenhouse: heat and light. Interestingly, the traditional European-style greenhouses were developed in the low countries of northern Europe as a response to low level of predominantly diffuse light prevalent in the winter time (think cloudy, overcast winters). This design was brought to this continent with little consideration for the differences in climate and latitude encountered here.

A greenhouse that is better suited to our winter conditions is a passive solar greenhouse. These greenhouses are designed to accept and enhance the direct sunlight and heat from the south while preventing heat loss by insulating the north, east and west sides.

Just this past December our greenhouse went up. Although currently empty (we still have to design out and build the interior) we’ve been receiving a ton of interest and questions about how we designed the structure itself. So, here are some photos (including a nifty tim elapse slide show of the construction) and a brief description of the structure.