Greenhouse Basics

There are basic engineering principles that have to be followed for a greenhouse to function properly, especially a passive solar greenhouse. It is shocking how many greenhouse companies do not follow these principles. Most of them have not changed their technology in more than 80 years! Follow the list below and you will build a great greenhouse!

  1. Orientate the long sides of the greenhouse facing North and South, with the shorter sidewalls facing East and West.

  2. Create convective ventilation from the low sidewalls to the high roof vents. Position the roof vents on the high wall instead of the roof at the highest point of the ghouse.

  3. Size your exhaust fans correctly. The magic formula is the calculate the cubic footage of the greenhouse and have enough fans to exhaust that number in 1 minute. For example a 12’ wide x 18’ long by 9’ high ghouse =1,944 cubic feet. A 2,000 cfm exhaust fan is well matched for this size. Anything smaller will allow heat to build while the fan is running.

  4. In Summer heat, shade the roof blocking 70-90% of the sunlight. The shade fabric goes on top of the roof (not inside, this is a classic mistake) and is a mesh construction, made from ballistic nylon, allowing wind to safely pass through.

  5. Size the vents correctly. The magic formula is 1/2 of the length needs to be roof vents. The sidewall vent or vents needs to be large enough to feed the roof vents and exhaust fans with enough air for cooling.

  6. Orientate your airflow correctly. Draw vented air across the length of the greenhouse from low to high.

  7. Ensure that your automated vent openers are strong enough to withstand high winds. Otherwise the wind will “rip out” the vents.

  8. Anchor the greenhouse strongly to the ground. Otherwise the wind will lift the entire structure and it will become a tumbleweed!

  9. Structural framing needs to be strong enough to withstand the weight and force of snow, rain and wind.

  10. The glazing material needs to be insulated and warrantied against hail. Maximum light transmission of 82% or higher is optimal. 8mm polycarbonate twinwall is the minimum thickness recommended. Glass is not insulated, is heavy and is not warrantied against hail or breakage.