The TRI-LEA-EM dome was designed to be functional as an all weather shelter for visiting groups, as well as a practical demonstration of energy efficiency and self sufficiency. You can read details on the building "system" here. We'd be interested in your comments! Links are given to the web pages of suppliers of some of the components. If you go there, use your browser "BACK" button to return to the TRI-LEA-EM site.

Dome Shell

To understand a geodesic dome, think of a soccer ball, made of five and six sided panels. Cut the ball in half, turn one half so the open side is down, squash it slightly, and you have a good model of a geodesic dome. The nicest thing is that the inside of the dome is free of any supports, as the load bearing is all carried by the shell. The TRI-LEA-EM dome is designed by the manufacturer for an 80 pound per square foot snow load and an 80 mile per hour wind - fairly severe conditions.

The TRI-LEA-EM dome is an Oregon Dome "Pioneer" model, nominally 50 feet in diameter, and 21 feet 3 inches high. It consists of 30 -10 ft x 8.5 ft x 8.5 ft triangular panels which bolt into 6 pentagon shapes and 30 -10 ft x 10.5 ft x 10.5 ft triangular panels which bolt into 5 hexagons. Each panel is framed by 2 x 4 Douglas Fir (Select Grade - stamped to allow a stress of 2250 psi) at 16 inch centres, to which is glued and stapled 7/16 inch oriented strand board (OSB). Panels are bolted together with about 375 -1/2 inch bolts. The drilling of the holes as received from the factory was perfect - not one hole had to be redrilled. Fit of the panels was excellent! 5 trapezoid panels 20 ft long at the bottom and 10 feet long at the top fill in the gaps at the bottom of the dome, and allow vertical surfaces for doors and windows. Jack Lydick of Lydick's Domes Unlimited (representing Oregon Domes) supervised the assembly and made the job easy. A team of about 15 volunteer workers (see the "Thanks" page) only two of whom had ever seen a dome erected before completed the shell assembly in about 7 hours on July 18th, 1998.

The shell exterior is insulated with 1 inch "Exeltherm" R 7.2 insulation, over which is applied 1 inch of additional insulation bonded a 7/16 inch OSB nail base as supplied by Oregon Domes. Some 4000 - 4 inch wood screws attach the exterior insulation to the dome structural framing - not a difficult job, but time consuming. Two to three workers completed this job in about 3 weeks. This exterior insulation minimizes the thermal bridging which would occur if insulation was installed between the stud spaces only.

The exterior shell is covered with 15 pound tar paper (self adhesive ice and water shield waterproof membrane was used instead on the low slope top pentagon and canopies for additional waterproofing). Finally, the shell was covered with 132 bundles of 235 lb EMCO BP RoofMaster Asphalt shingles. Installation of the shingles was simple, but somewhat time consuming as many shingles are cut for the triangular panels, but the amount of waste was not excessive. Shingling took about 2 calendar months, but that was because work progressed only in evenings and Saturdays by 2 or 3 amateur roofers. The bottom two-thirds of the dome was shingled from the ground by ladders, the top third was shingled by hoisting the shingle bales up through a skylight opening at the top of the dome, and working up from the two-thirds point while attached to a safety line secured at the dome top. After getting used to it, the task went well. We found that scaffolding was not too easy to work from for the shingling because of the inward sloping walls.

3.5 inch R13.5 Roxul mineral wool insulation is placed between the stud spaces on the interior of the dome, covered by a 6 mil vapour barrier, tightly sealed at all seams with "acoustical sealant". Because the dome shell is a closed cavity wall (similar to the vertical wall in conventional wood frame housing) it is important to maintain an intact vapour barrier to avoid trapping moisture in the cavity under the outer insulating layer. Actually, the exterior insulation helps by maintaining the temperature in the interior of the wall cavity above the dew point which helps to reduce moisture condensation problems. A 0.5 inch gypsum board surface completes the interior. The total shell R value is ~ R29.

Vertical walls (in "natural space" openings) are insulated on the exterior with 1.5 inch "Exeltherm" (R10.8), and on the interior with 3.5 inch (R 13.5) Roxul . Vapour barrier and 0.5 inch gypsum board complete the inside. The exterior surface is covered by 4 ft x 8 ft panel Canexel vertical shiplap wood fibre siding. The total wall R value is ~ R26.

Foundation

8 inch reinforced concrete walls, 4 feet high are supported by reinforced concrete footings 36 inches wide x 12 inches deep under the pentagon (load bearing) walls, and 16 inches wide x 8 inches deep under the natural opening (non-load bearing) walls. The exterior surface of the walls is coated with damp proofing from the top of the footings to the grade level (about 8 inches below the top of the foundation wall). The bottom of the footings are required to be 4 feet below grade for frost protection. The extra deep and wide footings were required to provide for an 80 pound snow load on the dome, coupled with a clay subsoil.

Foundation walls are insulated to footing on interior side with 2 inch R10 Styrofoam SM, and for the upper 2 feet on the exterior side with 2 inch R10 Styrofoam SM. The floor perimeter has a full thermal break to minimize heat bridging from the floor to the exterior.

Floor

4 inch coloured concrete, on reinforcing mesh, is poured on 4 to 8 inch deep reinforced "ribbon" footings (installed below future wall locations). Below floor insulation is placed for 4 to 6 feet from the exterior walls with 2 inch R10 Styrofoam SM insulation. The floor is uninsulated in the centre to provide maximum thermal mass benefit. (The majority of heat loss is to the perimeter, rather than straight down). When the building is heated up, it will be slow to change in temperature. A 6 mil vapour barrier is continuous below the floor.

1400 lineal feet of 7/8 inch POLY PXC Radiantec heating pipe is installed in the floor slab, fixed every 1 to 2 ft to the reinforcing mesh in 7 spiral loops. These comprise two heating zones for future in-floor fluid radiant heating, one zone in the main hall, and the second zone in the area containing the washrooms and kitchen, to enable preferentially heating rooms containing piping. At this time this in-floor heating has no heat source, but it needed to be placed before the floor pour - as later would be too late. A future plan is to place a stainless steel loop behind the wood stove and circulate hot water in the floor.

Windows & Doors

Windows are LoE² Argon Gas Filled manufactured by Repla Windows using Cardinal Glass Industries Energy Star Windows with an R value of 3.7, one of the best available for 2 pane windows. Doors are R 12 insulated steel doors, with Low E window inserts. Skylights have 2 acrylic lenses, R ~ 2. Windows are situated to make maximum benefit of passive heating, warming the insulated floor mass, as well as providing a bright interior.

Energy Needs

Construction energy needs (lighting, charging drill batteries, etc) were met by 2 x 15 watt ICP solar panels charging one 12 volt deep cycle battery, rated at about 180 reserve minutes. (~75 Ah or 900 watt hour capacity). A 100 watt Statpower inverter powered low demand AC loads. A 2300 watt Homelite gasoline powered generator was used on occasion for high current draw tools.

Heating will be by a Blaze King Catalytic wood stove rated at 53,000 BTU/hr maximum output, which has a 40 hour low burn time and 79% efficiency. The long burn time of the wood stove and large thermal mass in the insulated floor will permit long periods with little attention.

Because the building envelope is tightly sealed, mechanically assisted ventilation will be provided through an Air Changer air to air heat exchanger which is 85% efficient at recovering heat from the exhaust air and which supplies tempered fresh air to the interior of the dome.

Electrical energy needs for the building are supplied by 550 watts of solar panels (Shell Solar /Siemens SM-55 panels), a battery bank of 8 x 6 volt deep cycle batteries arranged as a 24 volt 400 amp hour capacity (Trojan L16 cells), and a 2.5 kW (Xantrex /Statpower) Prosine inverter. These particular solar panels are no longer available, but comparable ones can be seen in the link. A Homelite gas generator can be used to charge the battery bank in the event of high load demand during periods of low sun or wind.

The well insulated floor provides a thermal storage bank for heat entering the building via the south facing windows, or produced by the wood stove. Insulation levels in the dome shell and walls can only be considered moderate, but considering the building as a system reveals that the heat required by the building to raise the interior to + 20C (68F) on a day when the outside temperature is -20C (-2F) is 7888 watts (25,600 BTU/Hr)

Environmental Comments

Wood is a renewable resource, and the growing tree does absorb carbon dioxide from the atmosphere. While burning the wood does release the carbon back into the atmosphere, allowing it to decay in the forest does the same - although more slowly. The forested area at TRI-LEA-EM does provide a sufficient number of fallen trees to provide the fuel, and annual tree planting is carried out - replacing more than burned. The catalytic converter on the Blaze King stove is expected to reduce pollutants in the smoke by about 90% and use less wood than a conventional stove, so it becomes the preferred indigenous environmental choice for heating for us. We would not expect the choice to be the same in a city!

Your Comments?

We would be interested in hearing your comments on our project. You can e mail us at <3trileaem3.bmts.com > BUT remove the two-3's inserted to cut down on junk e mail.