Page 118 - Zero Net Energy Case Study Homes-Volume 2

CASE STUDY NO. 11
SOL LUX ALPHA
(Right) Wall section detail with manufactured wall panels, showing framing size and insulation location.
project, decided to invest in it. The two people formed a limited liability partnership, Sol Lux Alpha LLC, to develop the project and realize the cutting-edge goals. (Name derivation: “Sol” means “solar-powered”, “Lux” means “luxury apartments” and “Alpha” means “the first of its kind”.)
Project Process
Building Program
The financial analysis set the program at four condominium apartments of 1,800 gross square feet each, the maximum size for a single-story unit on this site. With the ground floor level given over to parking and vertical circulation, and a deck at roof level, the building as realized is six stories high, a mid-rise development and at scale with this neighborhood. The floor plate of each level also contains the two required exit stairs and an elevator that provides direct access to each apartment with an electronic access card.
Each condominium unit consists of three bedrooms, two bathrooms, an alcove office and a gen- eral living area. The kitchen uses an induction cooktop and electric ovens.
Site Constraints
The small size of the lot in the urban environment was an obvious constraint on the planning, and the setback requirements in this part of the city would have made the project infeasible. Specifi- cally, zoning required a rear yard setback of twenty feet and side yard setbacks of zero feet on each side. The developer requested a simple “exception” to this aspect of the zoning ordinance rather than a “variance”, which would have required a public hearing process to build to “zero lot line”. This was granted by the city zoning administrator because of the project’s innovative energy features and ZNE design. After these were discussed at a community public meeting, there were no objections to the project as proposed.
Low Energy Design Strategies
Obtaining the Passive House certification set the approaches to the features and systems for the building, as discussed below. Various options were evaluated for their impact on cost and schedule as well as energy efficiency, as is usual for speculative building projects.
Building Envelope — Insulation and Windows
The developer, facing a cost/profit issue with regard to construction time on a site with limited access, opted to use a manufactured wall panel system. These panels could be pre-made with the thick insulation levels required for Passive House certification. Given the strict airtightness limits required of the building skin (0.6 ACH50), which could be pre-tested at the factory, the wall panels also offered an opportunity to save time during the testing phase.
The final advantage of this manufactured wall panel approach was in building the many layers of the wall assembly required for the 2-hour fire rating. (See wall detail on the opposite page.) It was deemed to be faster and easier to assemble these layers in the controlled environment of the factory than on site where the access and weather conditions would be difficult.
These expectations were not fully realized during construction; see the Building Envelope — Air- tightness and the Observations sections (below) for a discussion of the issues.
The manufactured wall is insulated with 5.5” blown fiberglass and four layers of fiberglass mat gypsum board for a total R-value of R=27. The unvented attic utilizes open-cell spray foam plus 11” dense-packed fiberglass to achieve a very high R=82. The wall does not employ a layer of exterior insulation board over the 2X6 studs as a method of reducing thermal bridging. An analy-
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Zero Net Energy Case Study Homes: Volume 2