Building the Suncube

George Matthews is a home builder in Chico, California.

The Suncube is attractive, comfortable, and efficient. Although winter temperatures drop under 30oF, utility bills remain below $35 per month (for gas and electricity combined).

Armed with a home equity loan, a contractor's license, and some knowledge of energy-efficient technologies, I built an affordable, passive-solar house in Chico, California. The house is a simple two-story box plus basement, 22 ft x 22 ft, with clerestory windows and the majority of glass pointing a few degrees off true south. East-facing glass is protected by covered porches, and the single 2 ft by 2 ft window facing west will soon be shaded by a young oak tree. The remaining glass looks north. All but two windows on the south side have custom corrugated steel awnings that let in the low winter sun and block it as it rises in summer.
 

To fully isolate the concrete from the soil, we covered it with Bituthane waterproofing membrane from the footing to above grade and then installed 1 inch Dow blue extruded polystyrene foam insulation board (R-5) over the Bituthane and taped all the seams. We also put the foam board underneath the slab above a polyethylene vapor barrier.
 

For the floors and roof we used truss-joist wooden I-beams. The floor joists are covered with 3/4 inch Comply which stayed flat after being soaked for over a month in the wettest winter California has seen in years. I specified structural grade Thermo-Ply sheathing made from 100% recycled cardboard for the shear panels. It turned out to be a poor nailing surface for stucco netting. In the future, I'll use 3/8 inch oriented strand board, which has more strength and rigidity, holds nails better, and is also made of a waste product.

Following the production-style version of OVE, my framer put a 2 x 6 everywhere interior walls meet exterior walls. I changed this by removing the studs and placing 1 x 6 nailers onto the back of the 2 x 4s that met the walls. This removed five 2 x 6s from the shell where they would have acted as undesirable thermal bridges. All headers in the house are insulated box beams, which use less lumber, insulate better, cost less, and are a lot lighter than solid wood. To screw the gypsum board onto those two-stud corners, we used plastic nailing clips, which saved about $100 worth of lumber and provided additional room for insulation. We covered the outside of the framing with 5/8 inch polyisocyanurate rigid foam (R-4.5).

In the stud walls, I had R-21 high density batts of fiberglass installed. The ceiling got R-38 with a foil-faced kraft paper radiant barrier stapled to the bottom of the top flange, providing space for ventilation.

At an Affordable Comfort conference, I learned that you only get full performance from fiberglass when it's neatly installed. Though the insulation contractor seemed eager to comply with my instructions-no gaps and no California stuff job-I spent about seven hours going over the whole job, trimming, tucking, and fluffing out the batts. I suspect that I have the most meticulously insulated house in the state.
 

I wanted a high visible light transmittance and the lowest U-value (heat conductivity) I could afford. I chose Norco vinyl-framed, double-pane, low-emissivity, argon gas-filled windows with a 3/4 inch space between the panes, attaining a low overall U-value of 0.35.

Since most doors are lightly insulated anyway, I decided they should all be windows as well. I used single-light insulated steel doors with steel frames and low-E glass. They let in loads of light and give the house a clean, modern look. They also don't crack, warp, rot, or expand and contract with the seasons.
 
 

Inside the Suncube, ceiling fans in each room help keep the house comfortable in summer when temperatures exceed 100oF. A whole-house fan draws in cool air at night. A spotlight and sconce provide additional lighting.

The dining and living areas have six 50-watt halogen bulbs, all set on dimmers. A clear, striated glass cone hangs above the dining table. Three sconce fixtures flood the walls and ceiling with light ranging from the soft glow of candles to a bright white arc. These cost only $27 apiece, including sconce, bulb, and dimmer. The clerestory walls have white outdoor-porch-style swivel fixtures with 50-watt halogen spots that I've adjusted to illuminate paintings. These function like expensive fixtures but cost only about $10 for the fixture, plus $5 for the bulb.

Opaque white inverted mushroom fixtures with 26-watt CFLs provide general lighting for the porches, hallway and two bedrooms. Activities like reading in the bedrooms would call for specific task lighting. Both bathrooms have simple 4 ft fluorescent shop fixtures fitted into site-built lighting soffits. Each fixture received the $5 bulbs that more closely approximate sunlight, rather than 99 builder specials.
 

Airtight houses must be properly ventilated. I took a tip from Home Energy magazine and installed a quiet 50 cfm (cubic foot per minute) Panasonic bath fan. The fan looks normal but makes almost no sound, uses just 17 watts of power, and is rated for continuous use. It is perfect for removing stale, moisture-laden air and bringing in a small amount of metered fresh air. Visitors are always surprised the fan is on.
 

At a price of $126,000 (including land) the house costs too much for most people in Chico. In the future, I won't build basements or raised concrete porches. I look forward to building a simplified, slightly larger, slab-on-grade suncube that will be a model of affordable, resource-efficient, small-lot housing.
 
 

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