My New Greenhouse
After last year’s greenhouse disaster, I put a lot of thought into the next greenhouse project.
What do I need a greenhouse to do for me?
The first time I saw the words “Solar Greenhouse” I thought, is that a joke? Of course a greenhouse is solar. But a solar greenhouse is exactly what I was looking for. Basically a solar greenhouse is a building that is super insulated in the roof and on 3 sides with a full southern explorer and a thermal mass.
Here are some of the basic principles of a solar greenhouse.
The biggest difference between a greenhouse and solar greenhouse is the sunlight goes straight through a greenhouse and right out the northern side. In a solar greenhouse there are 3 full walls and a roof that are insulated to trap the heat and reflect sunlight back to the plants and thermal mass. The roof of a solar greenhouse will usually have a steep angle to reflect even more of winter’s light to the plants.
A solar greenhouse is insulated like a house, the more the better. Every crack is filled and sealed, every draft must be stopped. Check the local building code for home insulation to get an idea of what is needed in your area. An R25 is recommended by the City of Mercier Qc., this is the minimum in my area. I achieved a R30 to R35 in the walls, roof and floor.
To maximize the solar heat collection in the winter the glazing must be oriented to true south. If true south is not possible the greenhouse can be oriented a little to the east to start warming the greenhouse as early in the day as possible. The correct angle of the glazed is the latitude plus 15° to 20°. In northern latitudes that is going to be 40° to 60°.
Insulated glazing is usually two pieces of glass with a layer of air or gas sandwiched between them. It can be any transparent material that can hold an air space. A very popular material these days is multi-wall polycarbonate glazing panels.
Last year I built a hoop house that looked a lot like a small commercial greenhouse but a solar greenhouse looks more like a shed. In my design I worked a hoop system into it that I think is going to work very well.
The solar greenhouse I am building is 12’x24’ and 10’ tall. The base was made of 2x8 p.t. lumber for ground contact and ¾” plywood. I also painted the 2x8’s with a water proof rubber membrane for some added protection. In the bottom of the base there is 1”Styrofoam sealed with Polyurethane Spray Foam and 6” of pink, for a total of about R35.
The walls and the roof are made of 2x6 spruce. ½ plywood on the roof and the walls are covered with 5/8 aspnit. All the gaps, cracks and seams where first sealed with spray foam from the inside (the small cans) and insulated with 6” pink. The interior is wrapped with white 6mil plastic.
On the outside, all the wood is covered with a Polyurethane Spray Foam (600 square foot kit 1” thick) for a total of R30. The roof is covered with tar paper and steel again for a total of R30.
The glazing is 2 pieces of 6mil plastic greenhouse covering on a PVC frame. A 3rd sheet of 4mil bubble plastic on the inside of the greenhouse will create an air space or a thermal barrier providing insulation for the glazing.
The thermal mass for my solar greenhouse with 300 square feet of glazing is 900gal, a row of 8 barrels stacked 2 height will provide most, if not all the heat that the solar greenhouse will need over the winter. I did install an 8’ electric heater as a back up for cloudy days
Construction is all most finished but I will be adding things for a long time.
Indoor Gardener October 2008
After last year’s greenhouse disaster, I put a lot of thought into the next greenhouse project.
What do I need a greenhouse to do for me?
- To stay where I put it and NOT BLOW AWAY!!
- To never freeze and always stay above 5°c.
- To be energy efficient. No outside power would be perfect.
- Room to GROW!
The first time I saw the words “Solar Greenhouse” I thought, is that a joke? Of course a greenhouse is solar. But a solar greenhouse is exactly what I was looking for. Basically a solar greenhouse is a building that is super insulated in the roof and on 3 sides with a full southern explorer and a thermal mass.
Here are some of the basic principles of a solar greenhouse.
- Use a thermal mass to collect and store solar heat.
- Have large amounts of insulation everywhere there is no glazing.
- For maximum solar heat in the winter the glazing must be at a correct angle and oriented due south.
- Insulate glazing to minimize heat loss.
- Natural venting in the summer.
The biggest difference between a greenhouse and solar greenhouse is the sunlight goes straight through a greenhouse and right out the northern side. In a solar greenhouse there are 3 full walls and a roof that are insulated to trap the heat and reflect sunlight back to the plants and thermal mass. The roof of a solar greenhouse will usually have a steep angle to reflect even more of winter’s light to the plants.
A solar greenhouse is insulated like a house, the more the better. Every crack is filled and sealed, every draft must be stopped. Check the local building code for home insulation to get an idea of what is needed in your area. An R25 is recommended by the City of Mercier Qc., this is the minimum in my area. I achieved a R30 to R35 in the walls, roof and floor.
To maximize the solar heat collection in the winter the glazing must be oriented to true south. If true south is not possible the greenhouse can be oriented a little to the east to start warming the greenhouse as early in the day as possible. The correct angle of the glazed is the latitude plus 15° to 20°. In northern latitudes that is going to be 40° to 60°.
Insulated glazing is usually two pieces of glass with a layer of air or gas sandwiched between them. It can be any transparent material that can hold an air space. A very popular material these days is multi-wall polycarbonate glazing panels.
Last year I built a hoop house that looked a lot like a small commercial greenhouse but a solar greenhouse looks more like a shed. In my design I worked a hoop system into it that I think is going to work very well.
The solar greenhouse I am building is 12’x24’ and 10’ tall. The base was made of 2x8 p.t. lumber for ground contact and ¾” plywood. I also painted the 2x8’s with a water proof rubber membrane for some added protection. In the bottom of the base there is 1”Styrofoam sealed with Polyurethane Spray Foam and 6” of pink, for a total of about R35.
The walls and the roof are made of 2x6 spruce. ½ plywood on the roof and the walls are covered with 5/8 aspnit. All the gaps, cracks and seams where first sealed with spray foam from the inside (the small cans) and insulated with 6” pink. The interior is wrapped with white 6mil plastic.
On the outside, all the wood is covered with a Polyurethane Spray Foam (600 square foot kit 1” thick) for a total of R30. The roof is covered with tar paper and steel again for a total of R30.
The glazing is 2 pieces of 6mil plastic greenhouse covering on a PVC frame. A 3rd sheet of 4mil bubble plastic on the inside of the greenhouse will create an air space or a thermal barrier providing insulation for the glazing.
The thermal mass for my solar greenhouse with 300 square feet of glazing is 900gal, a row of 8 barrels stacked 2 height will provide most, if not all the heat that the solar greenhouse will need over the winter. I did install an 8’ electric heater as a back up for cloudy days
Construction is all most finished but I will be adding things for a long time.
Indoor Gardener October 2008