Page 67 - Designing for Zero Carbon-Volume 2_Case Studies of All-Electric Multifamily Residential Buildings

Building Envelope – Windows
All the windows were replaced with double-glazed vinyl units7 that are compliant with the Cali- fornia Title-24 energy code. This was done in all the buildings, including Buildings 615 and 619. Originally, the latter buildings were specified to receive a more advanced window product, the “thin triple-pane” window 8, which has the high-performance characteristics of triple glazing at a significantly lower cost and with the physical characteristics of a double-glazed unit.
Overall cost and availability issues, however, resulted in the use of standard double-glazed units for the entire project.
Building Envelope – Airtightness
In new construction, this aspect of energy-efficient design and construction is conventionally carried out with meticulous attention to the construction details involving penetrations, openings and other sources of air transition from the exterior.9 During actual construction, this involves the manual application of airtight weather membranes, adhesive tapes and caulking. However, for existing buildings, these traditional techniques would be excessively costly or could only be ap- plied in major renovations.
Aerosol Sealing10 is a method of air-sealing that had been originally developed for duct-sealing and used in recent years for whole-house air-sealing in new construction. It has found some application also in the air-sealing of existing wood-frame buildings. This technique can result in major improvement of the airtightness of existing structures and can be cost-effective consider- ing the technology, time and materials involved.
With this method, the building is pressurized while dispersing an aerosol sealant “fog” to the building interior. As air escapes from the building through the leaks in the exterior envelope, seal- ant particles are carried to these air leakage spots where they adhere to the surfaces, effectively sealing off the leak points. The method works well for existing houses that are unoccupied and the interior surfaces and contents can be protected from the dispersing aerosol.
For occupied wood-framed buildings, this method obviously cannot be employed in this manner. If the occupied structure has an attic, however, the method can be partially utilized, sealing off the ventilated attic from the rest of the building, resulting in an improvement in the measured airtightness of the overall structure. This application involves installing the aerosol “envelope” to the attic space, air sealing the ceiling/attic surface from the attic side. All equipment and work activity during installation occurs in the attic space above the occupied space below. This was the particular approach taken using the aerosol sealing method in one building at Vera Cruz Vil- lage as part of the research study.
For a complete discussion of the aerosol sealing method, including details of how this methodol- ogy was applied at Vera Cruz Village, see Harrington et al11, referenced in the footnote below.
7 Cascade WinPro Window Series, dual-pane and low-e glass. U = 0.30, SHGC = 0.25.
8 See https://www.energy.gov/eere/buildings/articles/bto-and-berkeley-lab-help-drive-adoption- thin-triple-paned-windows
9 Nordbye, Terry, Air-Sealing Wood-Frame Houses and Buildings, 2023.
10 See C. Harrington, F. Meyers, D. Bohac, M. Anders, L. Genty, Aerosol Sealing of Existing Residences, 2022 ACEEE Summer Study on Energy Efficiency in Buildings, https://aceee2022. conferencespot.org/event-data/pdf/catalyst_activity_32318/catalyst_activity_paper_202208101 90427374_40df278a_eddf_4668_85d8_89b87b68e957
11 Ibid.
Designing for Zero Carbon: Volume 2
(Above) Originally specified for Buildings 615 and 619 but re- moved from the project scope due to cost and availability is- sues, the thin triple-pane win- dow has the same weight and structure as a double-pane window, but the low U-Value of a triple-pane window.
VERA CRUZ VILLAGE
CASE STUDY NO. 3
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