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The log cabin of the 21st century? A spacious, 3000 sq.ft. home that generates its own heating and air-conditioning? A structural envelope that can maintain an even, comfortable interior - cool in summer and warm in winter, even in a rugged climate like Kansas - without either furnace or air-conditioner?
That's what Michael Sykes claims for his Enertia building system. The Wake Forest, North Carolina, engineer/entrepreneur has developed a sustainable, closed-loop building system made entirely of renewable and recycled materials. The homes are constructed with double walls of solid wood timbers that combine structural and thermal storage characteristics. In contrast to the myriad components of a stickbuilt home, with nails, vapor barriers and tar paper, synthetic insulation, OSB or other sheathing, tape, siding, and paint, the Enertia homes has walls made of squared logs tightly connected with 10 in. Ardox spikes, gaskets, and a connecting spline of recycled polyethelyne.
The wood used, Southern yellow pine, is a resinous species that grows to maturity in 30 years, and is planted at the rate of 3.1 million seedlings per day by timber interests in the southern U.S. A building material created by photosynthesis, pine might be a "perfect: sustainable product, one that cleans the air of pollutants such as carbon dioxide as it grows.
Sykes uses this local resource in a unique way, assembling logs into a dynamic building envelope. Essentially it is a house within a house, a double-walled building that encourages air movement completely around the structure in an interior cavity.
Solar-heated air moves on its own from an atrium of south-facing windows up over the interior "roof" of the house. As this air cools, it sinks down past the north side, and over the concrete slab of the ground level. The mass of the 6-in. thick walls and solid-timber rafters gains, holds, and releases heat throughout the day-night cycle, a phenomenon of thermal inertia. The house becomes a living and breathing thing, says Sykes.
Siting is vitalSite parameters - topography, seasonal mean temperatures, the thermal capacity of the glazing selected - are reflected in the design of individual Enertia homes. Large window-walls and clerestories are placed to admit the largest amount of low-level solar radiation in winter, and the least amount of higher-angled summer sun. The foundation level is bathed in sunlight from windows in its partially excavated southern side. Houses must be oriented to a southeast-to-southwest solar "window"; however, the Enertia building is not as sensitive to south as other solar homes. The house depends for its heating on the solar energy falling on it, and for its cooling on the geothermal reserve of the earth below it. The concept is a new approach to home construction, and the structure must be built fresh from the ground up. Components cannot be integrated into or grafted onto an existing home.
Enertia efficiently uses solar power in two ways: passively, receiving the sun's energy, as in a traditional solar home; and actively, using solar heat as the driving force that circulates that energy. Though some configurations may require a small motorized fan or geothermal heat pump, most homes - even very large ones - can derive all needed heating and cooling without any utility-grid power at all.
Architectural aspectsFloor plans of Enertia homes are generous, open, and flexible. The exterior face of the squared logs can be milled to mimic wood sidings such as lapped cedar planks or rough-sawn boards; roofs can be metal, asphalt shingles, shakes - whatever is desired. The heavy timbers used have an ignition point far above that of framing lumber, and the Enertia house can qualify for lower fire-insurance premiums. The company sells plans for homes from 2,000 to over 4,000 sq.ft. Custom designs are also available; Enertia homes as large as 6,500 sq.ft. are being built. Homes may include such design elements as Craftsman-style corbels, kingposts, balconies, and projecting framework that are natural to the timber structure. Once designed, homes are milled to order and the wood is shipped numbered for fast on-site erection on a prepared foundation.
The future of the future houseThe inventor anticipates infusing the wood with desiccant salts to futher lower the humidity of the interior air, thereby improving the assembly's cooling performance in tropical climates. The firm now uses CAD to translate site-specific criteria - log dimensions, glazed openings, even cut-outs for junction boxes or shelving - into detailed shop drawings. The next step will be computer-aided manufacture, using site criteria to direct the actual milling of parts from a solid block of wood. The architectural and embodied-energy aspects of this "thermal flywheel" are demonstrated in the company's Web site at http://enertia.com.
Reprinted with permision of ARCHITECTURAL RECORD, a McGraw-Hill Publication, from the November, 1997 Issue, Page 218 |