Southern Exposure Trading Co. - Passive Solar Garden Habitat Domes

Pilot Project Pictures - Updated as Project Progresses

View Pictures here

Note: Project history is chronological, so scroll to bottom to see latest news.

Overview: Passive Solar Garden Habitat Domes -

I am starting a new phase of my business to build prefab Garden Dome Kits for delivery within the New England area. I will seek out local sources of materials and keep shipping to a minimum. Domes will come in one size - 29 ft diameter as this is best for creating the least amount of raw material waste during construction. The passive solar part is a large solar mass in the form of a 1600 gal water tank. On sunny days the heat stored in the tank from the sun helps to heat the Dome at night and on cloudy days. The tank is located on the north side of the dome and the dome above and behind the tank is covered with a reflective material that helps direct low winter sun to the tank and shades the tank from the summer high sun.

The dome is a standard 3 frequency geodesic with 3/8 of a sphere sitting on a 2 ft base wall and consists of 5 full hexagons, 6 full pentagons (one at top), and 5 top half hexagons. An example of calculating space for a dome like this is located here.

Details For 29 Foot Habitat:

Base Panels are approx 6 ft wide and are made of 2x6 Pressure Treated bottom sills, 2x6 Fir Studs, and 2x6 Fir top sill. Panels are divided into three sections, each filled with two sheets of 2" Dow Blue Styrofoam outdoor rated at R20. The inner foam sheet on each end is not installed until the panels are bolted together. Panels are bolted together with two 1/2"x4" galvanized bolts at each end. Exterior is finished with either Fir T-111 or Pine T&G. Other exterior finishes can be used depending on cost and personal preference. Panels are numbered 1-14 clockwise from North with the Door Panel at location 15. Inner panel walls are finished with 2 ft aluminum flashing.

Hubs are powder coated steel cylinders with welded tabs at the appropriate angles. There are 5 Pentagon Hubs, 5 Hexagon Hubs, 20 Corner Hubs, 5 Hexagon Base Hubs, 5 Left Hand Base Hubs, and 5 Right Hand Base Hubs for a total of 45. Each tab has two holes to allow for 2-1/4" Stainless Steel Bolts to attach each Strut. Struts are 2x4 Fir and are color coded for Pentagon Spokes, Hexagon Spokes, and Perimeters as they are different lengths. Struts are coated in Waterproofing Sealant to protect from moisture.

Glazing consists of 75 triangles: 45 for Hexagons and 30 for Pentagons made of double walled 10mm (3/8") Polycarbonate with an R value of 2 and 80% light emission (by Macrolux). Panel seams are covered with 3M 8672 Acrylic Tape. Two Vent Panels are fitted with Bayliss auto vent openers, one upper and one lower.

Passive Solar heating is mainly accomplished by storing collected solar gain in a large water tank. A 9 ft diameter tank 4 ft high is used with an EDPM rubber liner holding approx 1600 gallons. The Tank wall is 20ga galvanized sheet metal painted flat black to absorb solar radiation. The dome above and behind the tank is covered in a foil-bubble-foil material that aids in insulation and also reflects the low winter sun onto the tank as well as shades the tank during high summer sun.

Pricing: My Garden Habitat Kit is available for $9950 with free delivery within 100 miles of New Durham, NH. I basically pass on the cost of all materials and charge $25/hr shop rate for my labor to construct a kit in about 14 days.

Kit includes:

  • 15 Prefab Base Panels 2'x6' with 4" rigid foam R-20 insulation in 2x6 frame
  • 120 Prefab 2x4 Struts cut to length, predrilled, and color coded, waterseal treated
  • 45 Custom Hubs 4" with tabs: fabricated steel welded, drilled, and powder coated
  • 75 Prefab Polycarbonate triangular Panels 10mm (3/8") double walled R-2 plus galvanized screws
  • 5 Rolls 3M 8672 Poly Tape 2" for Polycarbonate Panel Seam sealing
  • 2 Bayliss MK7 Heavy Duty Auto Vent Openers for Hexagon panels to act as vents (one upper one lower)
  • 100'x2' Aluminum Flashing for base panel inner wall/perimeter raised bed lining
  • Galvanized sheet metal 20ga 28'x4', 20'x20' EDPM rubber lining, rigid foam insulation for Water Tank
  • Complete Stainless and Galvanized Nuts and Bolts for dome frame and base panel assembly
  • Your choice of either Standard Pine T&G Boards or Fir T-111 for base panel outer wall covering
  • Dow rigid Styrofoam outdoor rated R-10 2" insulation for under raised beds (some scrap pieces used for inner bed)
  • Entry Door is NOT included (too many options) rough opening for 36" wide door provided
You will need to prepare the site for the structure - level and recommend a 4" bed of gravel stone. Basic tools and assembly required. You can provide grid power or solar power for lighting, pumps, and fans. Since this is free standing and not permanently attached to a foundation, a building permit is usually not required thereby keeping your property taxes from increasing. Be sure to check with your local authorities to be sure (although it's easier to apologize than ask for permission). On Site assembly consulting available for $300/day. Can be assembled by two people in three weekends. Floor area of roughly 600 sq ft will leave about 300 sq ft of raised bed space after Water Tank and walkways are figured in. Using arched trellises over walkways and planting climbing varieties will increase growing space. You provide all materials to build raised beds using your own floor plan - I provide a basic plan that I will use should you wish to replicate it.

Construction and Assembly Progress:

As of February component pieces are complete and actual assembly of demo/prototype will not start until the ground has thawed (sometime in March) as a 30 ft diameter area needs to be leveled and prepared for the dome base. Base panels are completed and struts are cut. All insulation is cut to size. Polycarb sheets waiting for final dimensions and cutting (not until dome frame is up). A 3/8 dome does not sit completely flat at the half hexagons so some adjustments have to be made to get a flat profile to sit on the base. I added 11 degrees to the bottom of all struts that sit on the base which allows the bottom frame to now sit flat. See pictures for my test build where I made some engineering changes to cuts to get dome to sit flat on base. First assembly to make sure all angles and strut lengths are correct and test hub angles. Everything fits but tolerances are very tight so some pushing and pulling is required during assembly but everything ends up being very tight even before a final tightening of all nuts and bolts. Some unevenness along base but test build area is not perfectly flat and level so that affects the angles of the frame. Final build site that is flat and level should line up all sections evenly.

A good stretch of nice weather Mid April allowed me to grade the hill top with the tractor and bring in 8 yards of ledge stone (crushed granite). Insulation around base inside wall was put down and stone leveled. base sections were arranged and framing began. Once framing was complete, base was aligned to frame bottom as a dome is more like a membrane than a square box building and base is not exactly round. once everything was aligned, all base sections were bolted together and frame base was bolted to base panels. This makes a very sturdy structure and it will not budge. Next step is anchoring the base using 3 ft x 3/4" steel stakes pounded in at an angle through the middle of each base panel bottom sill. This is required as strong wind can overpressurize the dome and lift and move it like a parachute. Next is inner base wall (aluminum sheeting) and outer base wall (pine boards). Then cutting and installing all of the polycarbonate glazing panels, fabricating the two vent panels and entry door framing. Installed the 9ft diameter 1600 gal water tank. That completes assembly and installation of the kit components.

Outfitting the Dome - Raised Beds, Electricity, Watering System:

The raised beds were made from 320 concrete blocks stacked three high (24"). No reinforcement will be needed as the Compost at 18" deep will not force the blocks outward. Tank has a fountain pump and aerator as I will be raising Tilapia in the tank. Watering system is a 55 gal barrel filled with pond water as needed. It has a small pump and 50 ft coiled watering hose and produces just enough water flow to water plants in beds while using only 24 watts of power. Since I already had 240v power at the site (built Dome around old Wind Tower foundation) I wired the Dome for 120v with two 20a circuits. I use three 1.5w LED bulbs for night lighting.

As of the end of May, the Raised Beds are filled with 14 cu yds of Compost from Earthtenders and seedlings have been planted as well as some new seeds directly. A commercial fan was placed next to the entry door to help with ventilation as it gets beastly hot on a warm sunny day. I have already seen 98F in there mid afternoon. Tank Pond temp is up to 82F and all aquatic plants are growing. There are 25 Tilapia Fingerlings happily calling the Tank their home and are doing quite well eating algae and plants as well as fish food I provide. All updates from here on will deal with trial and error of growing different plants in a very hot summer dome and later how well the dome holds temperature during the winter and what plants do well at that time.

Dome Performance and Gardening Success:

After my first winter, I have discovered that Passive Solar heating will not work here in NH - we simply do not get enough solar gain in Nov and Dec. By Thanksgiving, my tank water temp fell below 55F and all of the Tilapia died. Tank temp dropped to as low as 38F and all of the pond plants died. Dome air temp would be a nice 75F on sunny days, but in the 30s on cold nights. This spring, I have drained and removed the Tank and extended the raised beds where the tank was, leaving room to install a traditional form of heating, probably a Pellet Stove as that is easiest to restart daily in the evenings as opposed to a wood burning stove which takes over an hour to get a good fire established. I have also ordered some sun shade screening to block some of the solar gain in summer as it gets over 120F even with both vent panels open and a large 30" fan blowing air through the entry doorway screen door. Because of the extreme temps in summer, I was using over 25 gallons of water every day for irrigation. I have put together the components to install drip irrigation in the dome just like I have in the outdoor garden. This is a project of discovery and mid course corrections. Hopefully I will have things tuned in enough to have a year round garden this year. Very cold spring so far, seedlings are started but behind.

Fall 2011: Sun Screening worked great - reduced temps in the dome on a hot sunny day by 20F. I also added some misters coming off of the drip irrigation system which when on drop the temps another 10F so I can go from 120F to 90F. I have drained, disassembled, and removed the 1600gal water tank. This made room to expand the middle raised bed by another 40 sq ft and the perimeter by another 10 sq ft. I installed a Pellet Stove and run it on nights when the outside temps go below freezing, keeping it in the 50s inside. Although I will be buying and burning wood pellets, I will have good growing temps year round now.

Links to Dome Information:

Colorado Source For Garden Domes
Different Dome Styles

Local Products or Services Used:
  • Middleton Building Supply, Middleton: Lumber, Insulation, Concrete Blocks
  • Rimol Greenhouse Systems, Hooksett: Macrolux Polycarbonate Sheets
  • Fastener Warehouse, Portsmouth: Nuts and Bolts, Screws, Tape
  • Steve Haendler, Durham: Hub Fabrication
  • Color Coatings, Wakefield: Powder Coating Hubs
  • Collins Sheet Metal, Berwick ME: Tank Panels (3x10ft)
  • Barron Brothers, Farmington: Ledge Stone
  • Barton Lumber, Barnstead: Base Panel Outer Finish Boards
  • Earthtenders, Farmington: Compost for Raised Beds (no topsoil/loam used)
  • Lowes: Aluminum Flashing, Vent Panel Hardware, Doors, Sealants