Plants are THE Best.

I love plants and I especially love visiting greenhouses in the winter. Stepping into a warm, humid room and inhaling the thick scents of soil and tropical blossoms on a cold winter day really makes me wonder why I live in Saskatchewan where winter is 11 out of 12 months of the year. I’m kidding, winter is typically only October through April.

Commercial greenhouses provide a quick escape from the harsh elements of winter; they offer a tropical oasis just feet away from the blistering winds and snow. Unfortunately, the exterior walls of most traditional greenhouses are made entirely of windows which means they are very poorly insulated and have huge heat losses during cool months. I like to think most plant lovers also care about the earth; but heating traditional greenhouses in the cooler months has significant environmental impacts associated with poor heating efficiency.

Every spring after the snow melts and the tulips emerge, my fellow Saskatchewanians and I flock to commercial greenhouses in huge numbers to purchase trays and trays of bedding plants and starter garden plants. Yards quickly go from the drab grey of melted snow banks full of grit and dirt to lush flower beds with bright pops of colour in a matter of weeks. This drastic change is especially impressive when one considers the frost free season is mid May to mid September (if we are lucky). Novice to seasoned gardeners and plant lovers spend a significant amount of money and time on annuals (plants that only live one season) which have an extremely limited lifespan in the prairies short growing season.

Backyard greenhouses are an appealing addition/tool for the avid gardener as they can slightly extend the growing season as well as protect plants from harsh winds and hail storms. I’ve dabbled in a small greenhouse over one of my garden boxes. Let’s just say it wasn’t the success I had hoped for, but I was able to grow one very small watermelon and a few peppers. The greenhouse also helped extend my growing season a couple weeks on either end – I was able to bring seedlings out early without worry of frost and leave tomatoes out longer in the fall when the night temperatures drop significantly. It’s a lot of work for a short growing season, I’d love a greenhouse I could use for longer stretches of time, but the only way to do that is to heat it …or so I thought. I stumbled upon solar greenhouses awhile back and I am so excited to share my discoveries – 1) because these buildings don’t require artificial heating and 2) they have the potential to meet one of the trickiest building code requirements for greenhouses – spatial separations!

Solar Greenhouses

A solar greenhouse is different from a traditional greenhouse in that it is designed specifically for the climate and finds the proper balance between glazing and insulation to create a thermally stable structure(1). Solar greenhouses have significantly better heat retention compared to a traditional greenhouse as they have an insulated floor and north wall (at minimum) and, depending on climate, portions of the east and west walls may be insulated as well. A solar greenhouse also contains a thermal storage mechanism to release heat captured during the day into the greenhouse at night when the temperature drops outside.

Building Code Requirements

There are many Building Code requirements, such as proper egress and exiting, lighting, headroom clearance, etc but for a backyard greenhouse the main three things to consider are as follows:

Size

Check your local building bylaw for the minimum area requirements that require a building permit. In many municipalities, smaller buildings, for example a building with a floor area under 10 m², do not require a building permit. If this is the case, then the only limiting factors would be zoning requirements in terms of height, placement (setbacks), etc on lot.

Part 3

Most greenhouses are steel and glass or polycarbonate and therefore fall under Part 3 of the Building Code which requires professional designers. A structural engineer will be required to ensure things like wind, snow and seismic loads are accounted for. An architect or professional engineer may or may not be required for a small backyard greenhouse – it is always best to check with your local municipality.

Spatial Separations and Construction Requirements

The biggest Building Code hurdle of a greenhouse is addressing the spatial separations.

If you want fully glazed walls to allow all that sunshine in, you are looking at building a minimum of 5 m from the property line for a small backyard greenhouse but significantly more for a larger greenhouse.

Insulating the north wall, and potentially portions of the east and west walls drastically lowers the percentage of unprotected openings in these three sides which can allow for more flexibility in placement on the lot.

The exact distance from the property line depends on dimensions of the greenhouse, see Subsections 3.2.2. and 3.2.3. for more information on construction requirements, limiting distance and exterior wall construction requirements. Some relevant Kilo Lima posts to read if these terms sound foreign to you:

• Building Classifications in Canada
• The Nuances of Occupancy
• What in the Unprotected Opening?
• Fire Rated Glass Explained
• Wind Load: It’s a Breeze
• How to Apply Climatic Data to Structural Design
• Egress vs. Exit?
• Hey Building Owners – Read This!
• Architects and Engineers – When are they Required?
• What Does the AHJ Want to See?

In Summary

Two of the major drawbacks I see with year-round (or three season) greenhouses are limited options for placement on lots to meet spatial separations (percentage of allowed unprotected openings and wall construction requirements) and the high heating costs in cooler months. Solar greenhouses may offer easy solutions for both of these issues as 1) they do not require all walls to be fully glazed making it easier to meet spatial separation requirements and 2) they use the power of the sun combined with a thermal bank for heating therefore there are no ongoing heating costs. 

Recommendations

• Plan plan plan
• Read local bylaws carefully
• Engage a professional designer who specializes in Building Code for a greenhouse that requires a building permit

References

(1) Schiller, Lindsay and Marc Plinke. 2016. The Year-Round Solar Greenhouse Greenhouse. New Society Publishers, Gabriola Island, Canada.