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Bringing Green Home

by Doug Pushard

Below is an expanded version of the article published in eco-structure magazine May-June, 2009 edition, page 24. This version includes more detail on the installed rainwater catchment system.

Converting a shed to a home office in Santa Fe, N.M., took time, research and planning, but was worth the effort. By investigating products and working closely with the contractor, the 700-square-foot (65-m2) home office now is in business.

Because temperature swings are common in New Mexico, a basement below the shed helps regulate temperatures year round. Using the Earth’s constant temperature of around 55 F (13 C) and moving air from the warm parts of the shed to the cool sections in the winter and vice versa in the summer, the need for an HVAC unit was avoided. The basement walls are concrete block and covered with 1 inch (25 mm) of insulation board for an estimated R-value of 14 to 16.

An addition wiith adobe shed was built onto the existing 300-square-foot (28m2) shed. Because adobe has no rated R value, the exterior of the adobe walls was covered with 4 inches (102 mm) of spray-polyurethane insulation, resulting in an estimated R-value of 24. With the abode, insulation, rough coat and natural stucco finish, the walls are nearly 1-foot (0.3-m) thick. The basement walls are concrete block and covered with 1 inch (25 mm) of insulation board for an estimated R-value of 14 to 16. The 6 inches (152mm) of spray-polyurethane foam on the roof has an R-value of 36. The spray foam is covered with stucco barrier and keeps the office cool in the summer and warm in the winter.

Double-pane, low-E windows and skylights are fitted with automated controls to open when the interior rises; they lose in cold temperatures and when it rains. Open windows and skylights work with ceiling fans to create cross ventilation.

Heating is accomplished primarily through the solar-thermal system installed on the roof. The solar panels are tied to radiant-floor heating installed in the concrete basement floor; the heat rises naturally warming the entire shed. The panels also provide hot water to the office and auxiliary heat for the main house. About 100 F (38 C) water is furnished to the main house’s boiler, saving energy in heating water for the main house. A fireplace, capable of putting out 26,700 Btu per hour, provides secondary heat to both floors of the office.

The office's bathroom features cabinets made of locally milled wood, a low-flow showerhead and a dual-flush toilet. To further save water, while excavating the basement, a 1,600-gallon (6,056-L) below-ground polypropylene cistern tank was installed. A below-ground tank was used due to the small yard and the desire to capture precipitation year-round.

All downspouts on the back of the main house and the rainchain installed on front of the new office are piped underground to the tank. The roof canales are screened to prevent large debris from entering the system and all of the downspouts drain into sump boxes which include a filter material to capture smaller particulates.

The main house and office 2,400 square foot roofs are capable of capturing more than 18,000 gallons (68,130 L) of rainwater per year.

A submersible pump, equipped with a float, is installed in the tank. The float disconnects the electrical current to the pump if the tank water is low; thereby, preventing the pump from burning out due to running when there is little to no water in the tank. The pump is wired, via high voltage, to a motor relay switch which in turn is connected to the irrigation controller. The irrigation controller signals the motor relay, via low-voltage, to either turn on or off the pump. Also connected to the irrigation controller is a rain sensor which disconnects the common circuit to the motor relay if it has rained; thus preventing the controller from turning on the pump.

The installed rainwater harvesting system cuts the use of city-supplied potable water in half in most summer months and typically eliminates it totally in the spring and fall.

The office complements the main house aesthetically while maintaining a low carbon footprint. With the solar-thermal system tied to the main house, a rainwater-catchment system; and low-energy features throughout, it has not added to utility bills.

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