The Complete Greenhouse Design

Alrighty, enough of the boring required stuff. We’re going to talk about my favorite part, the complete greenhouse design.

How the Project Evolved

This project was in the planning and wishing stage for over a year. We originally wanted to start with something small like a shed or a small off the shelf greenhouse. Then I decided maybe we could pull off a small geodesic dome that we would cover with greenhouse plastic.

We then started talking about our long term plan and what our potential goals for a greenhouse were. Would this be just a covered spot to tinker with some hydroponics stuff for fun? Do we just want an excuse to get outside? Or could this be something more? Here are some examples of what the “more” could be.

  • What if we could come up with a feasible way to grow quality produce locally and sustainably year around in colder climates?
  • We knew we wanted to dabble in a soilless environment so we could really have control over every aspect of the grow.
    • We wanted to test different ideas and not have to wait a full growing term for results.
    • Some greens will grow from seed to harvest in less than a month hydroponically.
  • We knew we wanted to dabble in aquaponics.
    • We’d need to do something with the fish during the winter.
    • Need fairly dependable, controlled environment.
  • My brother and I are software engineers and wanted to incorporate those skills in some way.
    • Bring on the automation!
  • Eventually, one of the above ideas could turn into something more.
    • Could a hobby turn into a paying gig?
    • What aspect would have the most interest?
    • Could this be a teaching platform?
    • What typical problems with cold weather greenhouses cold we try and solve?

We talked about a lot of other stuff as well that didn’t quite make the list. We’ll revisit the pie in the sky ideas down the road.

Enter the final design concept. From a high level, we decided to go with a larger permanent, insulated structure that would have enough space to allow us to explore these ideas.

Version 1

We determined that the dome would be 20 feet in diameter and almost 13 feet tall. The structure would be a 3v, 7/12 dome; this would give us enough space to experiment with ideas while keeping the build sane. 3v is the frequency of the triangles meaning the higher the frequency, the greater the number of triangles in the icosahedron and 7/12 is the percentage of the full sphere we will build. You can definitely build 3v domes larger, but you start running into issues like not being able to cut triangles out of 4×8 sheets. It’s usually better to up the frequency as you go larger.

So we knew we were building a dome, we knew we were going to have a decent sized tank for fish, and we originally wanted to try a few different hydroponic methods; media based flood and drain, deep water rafts, and grow towers. We also knew were only going to have polycarbonate on the south side of the dome and we’ll insulate and roof the north side.

In this version you can see the towers in the back, the flood and drain in the middle, and deep water rafts around the perimeter. Notice the large fish tank sunk a few feet underground and the gray triangles will be covered with plywood and roofed.

Issues with this design

  • After more research, we determined that the flood and drain system has the potential to be unreliable and would not be a viable method at scale.
  • The center bed made it super tight to work on the perimeter beds
  • If we wanted to sink the fish tank underground even a foot, we would either need to use a tank that’s meant to be buried or wall off the hole to prevent the tank from crushing.
  • We can optimize our grow tower space with a rotation based layout.

Version 2

In this version, we’re going to add more towers and arrange them in a grid five rows deep. This allows us to plant the front row on week one, week 2 we push the first row back and add fresh towers, week 3 push those back and add a new one, and so on. Once the rotation is in full swing, you’ll be harvesting a row of towers every week.

To solve the problem of not being able to bury the tank, we’re going to lower the floor instead. We will need to run the foundation 4 feet underground to protect against the frost anyways, so this isn’t a big deal.

Issues with this design

  • With more research, we determined that grow towers would provide too great of an opportunity for water to splash on the leaves of the plants as it cascades down the tower.
    • This is undesirable for aquaponics because we’re fertilizing the plants with fish waste and the produce most likely would be contaminated.
  • After more deliberation around the site for the building, we found that my back yard slopes around 8 feet over 20 feet. We’ll need to build up the base to keep the uphill portion of the dome above grade.

Final Design

As you can see, we made sweeping changes to the overall design. We moved the entrance to the basement which is now a walk out because of the hill. The basement is now a full 8 feet tall which effectively doubles our square footage. We moved all the fish and water conditioning equipment to the basement to reduce the load on the second floor and to maximize our growing area. This also gives us space for a seed germination cabinet and a small work space.

We also added a set of stairs to access the upstairs which will be the sole way to access the dome.

Upstairs we removed the towers and added another deep water bed. This bed will be where we grow our vine crops like string beans, tomatoes, and cucumbers. We’ll run them to the ceiling on trellis’. We are leaving a little free space in the middle for a wicking bed or some sort of tiered planter down the road and we’d like to dabble with mushroom cabinets in the back.

Material List

Now that we settled on a final design, we’re able to determine most of the materials we’d need for the build from the model. Sketchup counts composed items for you and can calculate the square footage of the objects. See below for a complete list of materials that we were able to aggregate from the model.

General StructureDome Structure
2x10x10steel strapping
2x10x8schedule 80 pvc pipe 4″x20′
2x12x12schedule 40 steel pipe 4″x5′
2x12x20 LVL beam
2x4x8crushed stone
4’x8’x3/4 plywood subfloorsump bucket
4’x8’x1/2″ plywood100′ foundation drain pipe
2×10 joist hanger2x6x8 foundation grade
Steel Building Support Column 2x6x6 foundation grade
spray foam insulation2x8x8 foundation grade
20’x100′ Black 6 mil Plastic Sheeting4’x8’x1/2″ plywood foundation grade
exterior screws 5lb – 3″4x8x3/4″ treated plywood subfloor
exterior screws 5lb – 1.75″
Transparent portion of roofExterior
6mm polycarbonate 4’x8′rubber washer screws
glazing tapebarn metal 12′
Butyl Rubber Tape 2″x100′barn metal 8′
Butyl Rubber Tape 3″x100′ice and water shield
All weather silicone
pvc moulding strips
Shingled portion of roof
roofing/flashing cement
roof felt
roofing nails

Final Thoughts

We’ll still be making some tweaks here and there as a result of the construction process. Things like joist and stud spacing to minimize framing cuts and roof modifications to facilitate connections between the dome and base building.

Even though it took a lot of time, we gained a lot of insight and solved many problems when creating the model. We also thought we were required to have a comprehensive plan to apply for a building permit before we found out that agricultural buildings were exempt from inspections.

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