Page 21 - Zero Net Energy Case Study Homes-Volume 2

PASSIVE HOUSE LOS ANGELES (PHLA+)
CASE STUDY NO. 6
Project Process
Building Program
The program called for 2,038 gross square feet on two levels, with a second-story deck that also serves as a carport. The footprint of the house is 900 square feet. The ground floor is intended as an open loft-like living space, including a home office and a full bathroom. The second floor contains three bedrooms, two bathrooms and access to the large deck. As part of the design program, the owner decided to make the house wheelchair accessible on the first floor for po- tential future needs.
See floor plans and building sections on the next pages.
Site Constraints
In a semi-urban site such as this one, plans to add a two-story structure to a property often elicit a neighbor’s requests for additional limitations on size and height through a discretionary review process, which may affect solar access or incidentally constrain the size of the solar photovoltaic (PV) system. This project complies with all applicable regulations of the Culver City Planning Code and no modifications or variances were required for the design as submitted. Since the city has adopted a version of the “By Right” approvals process3 for such residential projects, the discretionary review process was not required and the project was approved for construction as designed.
The existing one-lane driveway from the street, originally serving the existing house on the lot, provides required car access to the rear of the property.
Large cypress trees near the southern property line and southeast of the planned location of the house cast early morning shadow on the rooftop solar PV panels. The effect on rooftop solar PV performance was deemed to be minor when this constraint was studied.
Low Energy Design Strategies
This case study home was designed and built to the Passive House Standard and received a Passive House Certification in 2019. At the present time, this standard and the certification cover energy efficient design only—they do not address on-site renewable energy generation4 or energy performance verification. But they do set rigorous requirements for the usual design strategies for ZNE homes.
Building Envelope — Insulation and Windows
The wall construction, as typical of Passive House requirements, is heavily insulated. Since the location is in the relatively mild coastal marine climate of Southern California, 2X6 framing with blown mineral wool insulation5 was deemed sufficient to satisfy the Passive House requirement. A 1.5”-thick layer of rigid mineral wool insulation6 was added on the exterior of these studs to prevent thermal bridging, which brought the total wall assembly to R=31. Both types of insulation product are inorganic and fire-resistant.
3 http://apalosangeles.org/how-to-get-by-right-zoning-right/
4 Passive House is considering a new evaluation system based on the renewable energy gen- eration at the project site. See: https://passipedia.org/certification/passive_house_categories/ classic-plus-premium. PHLA+ achieves Passive House Plus in this new system.
5 Jet Stream® Ultra Blowing Wool Insulation by Knauf.
6 Rockwool ComfortboardTM 80.
Zero Net Energy Case Study Homes: Volume 2
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