And issues surrounding snow.
In the video below you will see the owner of the greenhouse explaining what went wrong with his greenhouse. His greenhouse is basically useless during the winter because he made the structure in the shape of a half cylinder, which means the upper part of the roof is almost flat and collects snow. What he should have done is made the roof peaked in a sharp triangular shape, so that the snow is forced to slide down the sides rather than collecting on top of the roof.
In the next video you can see how easy it is to build one of these half-cylinder greenhouses... which is great if you don't mind snow collecting on the roof. The clip is from "This Old House", an American TV show based in Boston, where they don't get as much snow as Northern Ontario does. Boston gets average annual snowfall of 43.5 inches. Sudbury meanwhile gets average annual snowfall of 103.7 inches. And then there is the issue of accumulation. In Boston, the snow is more likely to melt within a few hours or days. In Sudbury, the snow just piles up and rarely melts until Spring. Thus a greenhouse in Boston doesn't really need to worry about snow accumulation, but a greenhouse in Ontario does need to worry about it.
But there is actually a solution. DO MORE RESEARCH BEFORE YOU BUILD!
And if you are living in northern climate, then you need to choose a design that will cause the snow to slide down the sides of the structure.
Take the example on the right. Is it an improvement over the half cylinder design? Yes. Could it be better, also yes. The top and sides of the structure could be a sharper and steeper peak.
The design is very similar to the one shown in the "This Old House" clip, but it can definitely be improved by making the roof taller with a steeper peak so that snow is more likely to slide off with ease.
Would it really cost that much extra to just make it 2 or 3 feet taller? Or take that much extra time to build? No and no. So just make it taller, as a shallow peak really won't be doing its job of keeping the snow off.
Plus the taller the structure is, the more sunlight/heat it captures and traps inside the greenhouse, and you have more room for shelves up higher for a 2nd layer of plants.
So the builder of this greenhouse went for a more wood design, but they also designed the peak with adjustable vents so they can control the amount of heat being trapped in the greenhouse.
The wood structure with bricks, gravel and cement around the base suggests this is meant to be a more permanent structure, so they decided to be more thorough with their design.
The roof has a nice 45 degree angle peak, which should be excellent for keeping the snow from accumulating.
The extra cost of all the wood in this design means that they likely chose to make the greenhouse smaller for budgetary reasons, but on the plus side this design should last a lot longer.
#3. The Asymmetrical Peak Greenhouse
The peak does not have to be in the middle of the greenhouse. Indeed, if you are building the greenhouse next to an existing structure, you could just make the peak on one side so that all the snow falls down the other side.
The two sides don't need to be even either. If one side of the structure faces south, it might make more sense to make that side of the structure longer. In the example below they reused an older brick wall from a previous structure.
#4. The Pyramidal Greenhouse
You aren't stuck using a single peak running the length of the greenhouse. There are many other shapes you might consider, such as a pyramid-shaped greenhouse. It will take more effort to design and build a pyramidal greenhouse, but the single sharp pointed peak will definitely keep the snow off of it.
#5. The Geodesic Dome Greenhouse
This particular design works well in warm climates, but it won't be so good in a northern climate because the top of the roof is not steep enough. A way to fix this would be to make the top of the structure a sharper peak rather than a rounded roof.
#6. The Hexagonal Greenhouse
The example below fixes the design problem mentioned above by adding an extra section for a peak at the top, which also functions as a vent. The design is also fairly easy to build, and part of the structure is brick for added permanence.
OFF GRID ISSUES FOR GREENHOUSES
Rainwater off the sides of the structure could be collected into rain barrels, and thus used for the plants.
Ideally you should place any such rain barrels inside the greenhouse to prevent it from freezing during the winter, with pipes leading up to troughs. A valve and pipe system could be constructed to prevent water from freezing inside the pipes, but also for distributing water to the plants.
Some people will want electricity for venting the space, but that can be accomplished without using electricity by opening doors, windows and ceiling vents. If heat is still an issue you can also soap up the walls and ceiling of the structure, as the soap residue will block out sunlight.
Some people also talk about using a gas heater, electric heater or even a wood stove to keep their greenhouse warm during the winter, but if you are resorting to such things then you clearly designed a low efficiency greenhouse that is not insulated enough.
If you need more insulation, during the design process you could have simply added an extra layer of plastic with some space in between the two layers of plastic. This barrier acts as an insulator to keep the interior of the greenhouse warmer.
The guy in the video way at the top mentions adding an electric blower to blow air between the two layers of plastic, but this is unnecessary if you simply design the structure to have a few inches of space between the inner and outer layers of plastic.
The pros and cons of a double layer inflation are:
- Improved insulation.
- Protects from wind better.
- Can sometimes push snow off the outer layer.
- Costs more to build.
- Costs more for the electricity to inflate the outer layer.
- Requires you have access to electricity, which may be harder to get during winter months.
How to Fix a Half Cylinder Greenhouse and make it a Double Layer with a Peak
Basically all you need to do is build the 2nd layer and make the outer layer have a steep peak to keep the snow off. It doesn't matter if the inner greenhouse has a round roof because it is the outer layer that gets snowed on, and that is the layer that needs to be a steep peak to prevent snow.
Easy peasy lemon squeezy.
Some people are just making things harder than they need to be.
So what design would I choose?
Honestly, it depends on the size of the space and the budget I have allocated for the greenhouse, but I would probably go for the Asymmetrical Peak Greenhouse design and have it facing south. I would make the roof very steep with lots of room for shelves above. By making the structure taller, it adds more room for square feet of shelves for "growing space".
To feed a family of 4* during the winter a greenhouse would need to be fairly big, roughly 80 sq feet of "growing space" per person. So a family of 4 would need 320 sq feet of "growing space", which does not include where you walk/etc. The more space you have to grow the better, so 360 sq feet would be even nicer.
* So that estimate for feeding a family of 4 during the winter is based on the idea of each person consuming an average of 4 ounces of veggies per day. 16 ounces is 1 lb, so you need to be growing an average of 1 lb of edible food per day during the length of the winter. Different foods grow at different speeds and yield different amounts of food, so you really need to be smart/wise about which foods you choose to grow in order to get a greater yield per square foot of greenhouse garden.
If you have 3 shelves on each side of greenhouse (6 shelves total) and the shelves are an average of 4 feet wide by 15 feet long, that is 60 sq feet per shelf, x 6 = 360 sq feet.
Giving myself 4 feet between the shelves to walk and carry tools, this greenhouse would need to be a minimum of 12 feet wide and 15 feet long, plus the dimensions of the structure itself. So lets make it a bit bigger and go for 15 feet by 20 feet, just so there is even more space.
And if we make it slightly taller, maybe fit in another set of 4 feet wide shelves to grow 33% more food, since 8 shelves is clearly better than 6 shelves.
Another way to improve the structure would be to make it square, say with an interior space of 20 by 20 feet. With that shape you could have 2 aisles for walking (4 feet wide each) with 3 rows of shelves. So instead of 6 shelves, 9 shelves... and if tall enough for 4 shelves per row, then 12 shelves.
By then you are looking at...
4 feet wide, 20 feet long shelves = 80 sq feet per shelf. X 12 shelves = 960 sq feet of growing space.
That would be more than enough space to grow all the veggies a family of 4 eats all year round, even if some of the plants have terrible yields. You could be growing it and giving away excess food to friends and family members and guests.
20 x 20 feet of space isn't unreasonable either. Many backyards in cities have 400 sq feet of space available. In the USA it is true that backyards are shrinking, but many people would not have too much difficulty fitting in a small or medium size greenhouse into their backyard if they wanted to - especially anyone who lives in the countryside and has ample space.
So yes, for my purposes an Asymmetrical design facing south, 20 x 20 feet, and I could have 3 shelves in the south row, 4 shelves in the middle row, and 5 shelves on the north row. That would provide all the veggies my family and I would need, with lots left over.
Anything left over I could turn into jams/pickles/etc and give away or sell.
How do you fit the Plants in?
There are many ways to organize your shelves and space inside the greenhouse, so you will want to consider your options here too. The design below use PVC tubes and works well with any greenhouse that has slanted walls.
You might decide to use normal shelves, you might want your shelves to be tiered like steps, or inverted tiers...
Or you might even want the shelves to rotate with a crank so you can get easier access to shelves that are otherwise harder to reach.