Page 85 - Zero Net Energy Case Study Homes-Volume 1

MERITAGE PRODUCTION HOUSES CASE STUDY NO. 4
The attic spaces were built as conditioned spaces, with the SPF applied to the underside of the sloped roof structure. The attic space was then used for the mechanical heating, ventilating and cooling equipment in a volume that was maintained at an approximate temperature of 80 de- grees all year. In the warm climate of the location, this maintained a “cool roof” condition at the same time as reduced duct losses, air infiltration and the usual attic “greenhouse effect”.
The resulting overall R-values for the typical wall assembly comes to R-21 and for the roof as- sembly the total is R-28 (derated for framing factors that cause thermal bridging).
Windows and doors were specified to have thermal breaks, eliminating another potential source of heat gain/loss through the building envelope.
Building Envelope – Air-Tightness
The use of SPF contributes to the overall air-tightness of the house. In addition, gaskets were used at the top and bottom plates of the framing to control air leaks that normally occur at those locations. A Blower Door test was done at two of the houses as a quality control measure; it was found that the two houses averaged 3.0 ACH50, which is considered below the California Title-24 recommended standard of 5.0 ACH50 but greater than the Passive House standard of 0.5 ACH50.
It also indicates a sufficiently air-tight house to suggest that a ventilation system be installed with good air distribution to each space and a control system to manage the intake of fresh air. (See the following section.)
Heating, Ventilating and Cooling Systems
The houses are equipped with a high-efficiency air-source heat pump split system for heating and cooling (SEER 15, HSPF 9). The air distribution is via ductwork from the equipment located in the conditioned attic space and utilizing an advanced control system to manage fresh-air in- take, air-temperature and humidity.
Zero Net Energy Case Study Homes: Volume 1
(Above) First floor framing of a Sierra Crest house in prog- ress using Advance Framing method.
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