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Old Main          Mani Shop          The ARC          SPARC          TWARC           Permaculture Garden

Affordable Living in an

Energy Efficient Duplex

TWARC stands for Twin ARC. It encompasses many of the same principles as the SPARC but in a duplex. Both sides of the duplex have three bedrooms, two baths, a greenhouse, and about 1,300 sq. ft. Like the ARC and SPARC, it sits on a “slab of concrete floating on a bed of sand in a highly-insulated box.” This time the insulation includes 10 inches of foam on the inside of the box only. The box is built only to create a temporary form for the insulation. Once backfilled, the wooden box will decompose. Also similar to SPARC but different from The ARC, the bed of sand is heated through direct air flow from the passive solar greenhouses.


Double-wall & offset truss construction

Instead of using SIPs, this is the first HUG Campus project that uses traditional wood framing for the building, but with one big difference. It actually has two frames, one exterior and one interior, that never touch. The double frames are separated by 12 inches, offering the same insulation value of the SIPS. That space is filled with blown cellulose insulation. Because the frames don’t touch, it eliminates thermal bridges found in normal stud homes that transfer the outside cold directly through the wood to the inside of the house. The outside stud frame is 2x6 while the inside frame is 2x4.


The roof truss is another innovation that allows extra insulation at the corners. We use a “drop down” truss so that the ceiling actually hangs a foot below the top of the wall structure. This allows the wall insulation and the ceiling insulation to overlap, eliminating another common “cold corner” issue.

The drop down truss is an innovation to eliminate the "cold corner" issue, allowing the wall insulation and ceiling insulation to overlap.  

Double wall construction eliminates the SIPs while maintaining the foot-thick insulation. 

Double walls
Blown insulation
Sand Box
In-Floor Heat
Specialized windows


construction begins


Square feet
living area in each apartment.


Average monthly cost includes all computers, lights, appliances,
and heat.


Insulation value of the walls/floor/ceiling. 

3 / 2

Bedrooms / baths in each apartment.

Heating & Cooling Costs

Scaled to compare heating and cooling costs per square foot against a standard new home.

Old Main          Mani Shop          The ARC          SPARC          TWARC           Permaculture Garden
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