Page 38 - Green Builder Magazine Sept-Oct 2017

CREDIT: KAREN CULP PHOTOGRAPHY AND DESIGN

Air apparent. Casement windows, thermally broken frames and multi-point lock doors, which provide better air tightness, were installed to
improve energy efficiency.
A PASSIVE DESIGN downstairs. These eliminate the use of ductwork, increasing
Energy costs can be reduced by simply taking advantage of the efficiency. The units have the ability to vary capacity, which saves
movement of the sun. For the Chattanooga area, it is best to shade energy. It can run a little, when just a little is needed—which is most
any south-facing windows to eliminate direct sunlight in the summer, of the time—in a well-sealed, well-insulated home. Another feature
but allow for heat in the winter. Providing overhangs and vertical of this system is that it can still work effectively at temperatures as
shading elements helps to improve energy performance. On the low as -13 degrees. A Schneider Electric Wiser Air thermostat was
homes, the windows at the top of the house have an overhang, which installed and works as a control panel for the home. It has intuitive
allows the solar panels to pick up the sunlight, conserve energy, and scheduling and learning algorithms, which help to conserve energy
reduce excess heat, glare and ultraviolent radiation. in the home, and also has live weather alerts.
green|spaces wanted to seal house as tightly as possible, while also
A BUILDING ENVELOPE: WALLS, ROOF AND FOUNDATION making sure the home has enough fresh air. They used an energy
The design of the walls, roof and foundation can help achieve a recovery ventilator, which takes the air from outside and brings it
high-performance home. inside, then sucks it back out through the kitchen and bathroom.
VaproShield, a vapor permeable air barrier, was used on the walls to The system pre-heats and pre-cools the fresh air that is brought in
keep the wood dry. This secures a long life for the wood in the home. from outside.
Greenguard-certified open-cell spray foam was used to insulate the After installing the system, a blower door test showed a 1.67 air
walls. The crawlspace was sealed, insulated and conditioned with a changes per hour (ACH) rating in the home. The required Energy
10-mil vapor barrier and closed-cell spray foam. Star rating is 4 ACH; the nonprofit is anticipating that number to
The roofing material required something that would work well be lower in the next three homes.
with the solar panels, so green|spaces used a standing steel metal
roof. The solar racking can be clamped to the seams, with open-cell BETTER WINDOWS AND DOORS
spray foam between the rafters, instead of having to penetrate like green|spaces found that using Energy Star-qualified windows and
a regular roof. Also, it is one of the longest-lasting roof materials— doors allowed for greater efficiency. They meet standards for the
one that will outlast the solar panels—so it prevents the owner insulating value of glass, which is a U-factor less than 0.30, and
from having to remove the solar to replace a shingle roof and then standards for the amount of heat the window allows to enter the
reinstall the solar. home from direct sunlight, which is a solar heat gain coefficient of
less than 0.40.
IN THE AIR: HEATING, AIR CONDITIONING With that in mind, casement windows, thermally broken frames
AND VENTILATION and multi-point lock doors were installed to improve performance
The passive design also plays a role in keeping the house well further, through better tightness of the building envelope. Unlike
ventilated. Natural ventilation with high exhaust windows pulls air double-hung windows, which are pressurized at the top and bottom,
up through the house during months when active heating and air casement windows are pressurized on all sides, resulting in a tighter
conditioning is not necessary. seal and less cool and warm air entering the home. To ensure optimal
For heating and cooling, green|spaces installed two Mitsubishi tightness around the window, minimal expanding foam was applied
Hyper-Heat ductless mini split systems, one upstairs and one to the window frame.

36 GREEN BUILDER September/October 2017 www.greenbuildermedia.com

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