Zone 3 four season greenhouse - early project planning and brainstorm

2 days ago

Hi all,

New to this side of houzz! I typically lurk in the orchid forum. I'm in the early stages of brainstorming and planning a greenhouse for a zone 3b prairie climate in Saskatchewan, Canada (-35-40C/ -30-35F for a few weeks each winter), primarily for the purposes of orchid cultivation. I have zero engineering/building experience, and will be getting contractors to do the work as part of a custom-build home, so I wanted to gather some intelligence, and run the broad-stroke ideas by you guys before I do something stupid and expensive.

My concept (again, generated with zero experience/engineering background) is a 2nd floor greenhouse over an attached garage, facing south with the north wall against the house. My thoughts and reasoning are:

a) Provide maximum sun exposure by elevating it above surrounding trees/structures

b) Any potential leak issues would go into the garage below instead of the main house

c) Save real estate on the lot for backyard gardening (another passion)

d) Save on heating costs in the winter with one less exposed wall/floor, as well as potentially save on home heating costs in the winter too through passive heating and transfer to the rest of the house

Functionality: For my purposes, the greenhouse would have no soil, and will mainly accommodate small pots and frames with hanging plants. Size will roughly be 16 x 24ft (or bigger if I can get away with it), so not a gigantic space.

I'll be targeting 75-80% humidity, with buoyant air movement being important. I'm aiming ideally for 25C/80F days, 18C/65F nights in summer, and 20C/70F days and 14C/55F nights in the winter, with options for a warmer zone and a cooler zone.

Main issues I'm thinking about:

1) Humidity - how does one protect the house from 70-80% humidity in attached greenhouse situations? Is a moisture barrier on the exterior enough?

2) Heating - I realize running a subtropical greenhouse in zone 3b is expensive. I'm thinking in-floor radiant heating as a good (expensive) option (planning on having this in the house as well), but interested in passive heat storage ideas too. I've read about using water as a vessel for this - does it make sense to use water barrels filled with clean plant watering water for this purpose?

3) Cooling - our summers not too hot, typically 30C/85F highs and dry, but VERY sunny. Night-time temperatures fall to 17-18C/low 60sF. I'm worried about over-heating and don't know many resources on greenhouse cooling methods - I'm thinking ventilation, shade cloth and fans - are there automated options out there?

4) Shade - I think I can accommodate this by hanging higher light plants up above to shade the ones below

5) Snow/ice - we actually have pretty high winds, and snow doesn't tend to linger. The prairies also don't get as much snow as the coast/eastern part of the continent. I'm not sure how to prepare for snow/ice on glass, beyond having an adequate pitch on the roof and heating the greenhouse. If I have my way, there will be an outdoor 2nd floor deck where the roof can be accessed for sweeping.

6) Condensation - I'm worried about this, and plan to tackle it with air movement, radiant heat through concrete floors, and not letting humidity go above 80%. According to this link, I should be okay on the vegetation even at 55F, but I'm worried about condensation on the glass panes. Any other tricks that people employ?

Sorry for the long post, and what I imagine many naive assumptions and ridiculous ideas/questions. Is this all completely bonkers? Any wisdom to share before I start on this quest? Any other zone 3 four season greenhouse owners have "hindsight is 2020" lessons to share?

Thank you all so much.

Comments (8)

  • shavedmonkey (Harvey in South Fl.)Z10b

    This is a big challenge with a big bank roll, due to all the requirements. The best advice will come from someone who built one and is currently growing orchids in your zone. I am z 10b. It can be done. The price tag could be astronomical. I am known to take on challenges but the best advice and most economical on a relative basis will come from someone in zone 3.

    From a layout consideration I would enjoy the space for relaxation or entertaining. I would plan enough space to include a small table and some chairs. And maybe a chais lounge. It could be the best hang out of the property. Breakfast and the morning paper? A glass of wine and some music. I would prefer same as floor level as the house. with a masonry drained floor. Off the kitchen if possible. Then keep a bench of fresh herbs too. Maintaining comfort for orchids in z3 will attract humans. A very desirable destination to your property.

    Best Answer
  • arthurm2015
    2 days ago

    I really do not know what zone 3 four season greenhouse would look or feel like. Most large glasshouses in cooler climates are copying Tropical Lowland Climates. There was one in Wales UK that copied the the climate in California, South Africa and Southern Australia and grew the native flora from those places. A nice change from the usual.

    Orchids! Tropical Lowland, Tropical Savannah, Mist Forest. etc. You cannot grow them all in the one set of conditions!

    Hopefully, some of the real orchid growers in Northern USA and Canada will add to this.

    xmpraedicta thanked arthurm2015
  • xmpraedicta
    Original Author
    last modified: yesterday

    Thanks for the reply! I may not have been clear - I’m aiming to build a subtropical greenhouse IN a zone 3 climate!

    As for the conditions, yes - well aware of the wide range of habitats from which orchids originate ;-) I have no interest in growing South American cloud forest species, or Mediterranean terrestrials.

    I mainly grow East African and Madagascan Angraecum/Aerangis species, primarily “intermediate-warm” growing which is the vague orchid lingo we use for the temperature range described above.

    I’m less in need of orchid cultural info, more in need of greenhouse engineering help and how to create the conditions described above

    Thanks again!

    EDIT: I realize my original post may have been cross-posted into the orchid and northern gardening forumS when houzz asked me to choose ‘tags’. I’m new to this format (I’m used to the old gardenweb days) so apologies if my comment doesn’t make sense

  • xmpraedicta
    Original Author

    @shavedmonkey (Harvey in South Fl.)Z10b totally!! that’s the dream. I’m thinking hammock.

    What you propose - (a ground level structure) would be a very reasonable alternative. I’m apprehensive, but prepared, for the potential costs (to a degree - never done this before). I recognize the luxury and excess this represents, and I’m not proud of this....Thankfully in my industry, part of moving to this zone 3 horticultural wasteland were the economic means to make this possible.

    People here have 4 season indoor heated pools. I’m telling myself this is the same on a smaller scale...maybe that’s just false self reassurance though!

  • shavedmonkey (Harvey in South Fl.)Z10b

    Ground level attached to common living space is the spot. Due to the expense, failure and redo is not an option. Therefor a successful, experienced architect and or engineer with satisfied customers you can visit and interview. With good research this will be money well spent. It must be right the first time!

  • James _J

    I don’t have a greenhouse, yet anyway. It is something I have always wanted and have spent a lot of time thinking about how I would do it. I also work in construction, not residential but a lot of things carry over so here are my thoughts.

    I don’t know if you have checked with contractors for pricing yet but my first thought was that the framing of the garage was not intend to support that type of load so you will have to beef up the framing of the garage first which will add cost. I would imagine your garage is not heated so you will also have a hard time controlling the temperature. It will get hot on a sunny day but very cold at night.

    I do have a sun room on the south end of my house off of the living room. It’s just a narrow room with windows on 3 sides and I put 2 levels of glass shelves across the windows. This is where I keep my plants over winter. I like it because being attached to the main house it’s easy to access, and if I move it’s just another room in the house. The plants in the room take care of the humidity but I only shoot for 60% and everything seems fine. The down side is that it has wood floors so I have to be careful about spills and it’s kind of small.

    Ideally I would build a solarium type of structure off of my kitchen. I would build it partially in the ground to help control the temperature. I would put a cistern in under the floor and collect rain water. I would also have a back up heat source for power outages. The walls and floors would be stone and the windows and roof glass and aluminum. It would also need a door to the outside so I wouldn’t need to carry stuff through the house.

  • tsugajunkie z5 SE WI ♱

    From November thru February your sun angle is so low and the days so short that the need for supplemental lighting would negate the value of it being a greenhouse during that time...maybe even longer.


  • jane__ny
    8 hours ago

    I agree with Tsuga. Your lighting will be a problem.

    I grew Angraecums and Aerangis when we lived in NY, zone 5.

    I also had a sunroom attached to our kitchen which was on the second floor. Our house was built on the side of a hill and the back side of the house was raised 25 ft, thus a raised kitchen and sunroom. The sunroom did not have heat. Many times I would leave the kitchen door open to let heat in but couldn't do that in the dead of winter.

    I put all my orchids outdoors in early spring throughout the summer. Brought them in in September or when the nights started dropping into the 40's. I moved all into the house and put them under lights. We had floor to ceiling windows in our living/dinning room which faced S.W.

    Winter days are dreary, cloudy and grey. Not a lot of sun nor light. Phals did fine there but everything else needed supplemental lighting. Even then, the lights I used were not enough for certain species.

    I think your biggest problem growing the orchids you want will need supplemental lighting. If you heat the greenhouse you need to provide humidity. If you can attach it to the house, it would save a lot of work. Near the kitchen, even better!

    I was able to bloom my Angraecum/Aerangis every year.