I have been discussing my vision for an aquaponic garden/farm over the past week or so. I figure today I would start on the building to house it in. The greenhouse is intended to allow adequate ventilation and control of the growing environment when Mother Nature doesn’t want to cooperate. It needs to meet a few criteria:
- Reasonably inexpensive to build.
- Sturdy enough to withstand winters in southern Indiana.
- Large enough to house all of the aquaponic components mentioned in my previous post.
My initial idea for the structure of the greenhouse walls is to make use of reclaimed sliding patio doors, if I can find them. The sliding doors would allow me to open as much or as little as I want to the outside air, reducing my need for cooling in the Spring and Summer months. To fit my roughly 18×36 foot needs, I will need 18 6-foot doors. That’s six for each of the long sides and three for the short sides. I would use a pressure treated 4×4 in between each pair of doors, with a 4×4 sill at the bottom and two stacked 2×4’s for the top plate. As I go through the lumber requirements, this could get expensive so I might have to re-think the wall construction.
I’ll need some pitch to the roof to shed snow and runoff from the rain. My initial thought is corrugated polycarbonate because it’s clear, but in order to cover the entire roof, that will require 36 pieces and they cost almost $30 each. That’s over $1000 just in the roof, with nothing to hold it up yet. That’ll need some re-thinking.
This part I do have worked out. I plan to use vertical geothermal earth tubes to regulate the temperature in the greenhouse. At a depth of 12 feet or more, the temperature of the earth is reasonably constant (+/- 5-10 degrees over the course of the year). If we dig 12 6-inch holes about 20 foot depth and force air down a 4-inch pipe in each one nearly to the bottom, say 18 feet, the return air can be cooled (or warmed) by as much as 30 degrees or more. Directing the return air back into the greenhouse will heat or cool the building accordingly. Morgan Brown has a couple of good videos here and here that explain in more detail. I’ll experiment with four sets of three earth tubes, one in each corner, with “snorkels” in the hotter months to capture the hotter air near the roof. I will be able to remove the snorkels in the winter. If I find I need more heating/cooling capacity, I should be able to add them as needed. The output will be directed using ordinary 6-inch metal duct outside the 4-inch intake. I may also experiment with insulated 6-inch duct.
What have I missed in the plan for greenhouse construction? What other ideas do you have to make it even better?