JSW/D Architects

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Green Gulch Farm Housing, Marin,CA

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This new 8-unit building for the San Francisco Zen Center's Green Gulch Farm will be built according to the "Passive House" standards, a European-based approach that establishes goals for very low energy consumption. The dormitory is organized into pairs of rooms that share accessible baths and kitchenettes, and each room has access to its own outdoor patio or balcony overlooking the valley.

"Passive House" Energy Conservation & Green Building Features at Green Gulch Housing

Energy Goals
• Using the "Passive House" approach, this dormitory combines passive solar, super-insulation, triple-glazed doors and windows, airtight construction, and heat recovery systems for an efficient building that does not require conventional heating and cooling systems for comfort. The goal is to create a comfortable building which approaches "near net zero" energy use.
• For the Marin County GreenPoints checklist, 208 points were targeted out of a possible total of 275.

Siting and Building Envelope
1. Building oriented for maximum solar heat gain, to help counter the cool, often foggy climate of Green Gulch.
2. Triple-glazed windows and doors (R-values of 5.0 and 5.26) located for maximum day lighting and to balance interior light. Window frames are fiberglass for reduced thermal conductivity and window glazing has low-E coatings tuned to orientation. Windows are fixed or casement for minimal air infiltration. Fiberglass entry doors have an R-value of 66.
3. Thermal bridging avoided by use of careful detailing: plywood joints sealed and taped with 3M All Weather Flashing Tape; air-tight electrical outlet boxes used at exterior walls; air barrier below bottom truss chord; no openings into attic except by gasketed access hatch.
4. Insulation far exceeds state minimums: stabilized cellulose insulation of R-60 at attic and R-21 at walls, 3-1/2" of rigid Polyisocyanurate above the floor slab yields an R-value of 19.6.
5. Concrete mat slab contains 25% Fly Ash.
6. Ventilating rain screen provided behind both stucco and wood siding.

Building Construction & Materials
7. Framing is FSC-certified at 24" on center for efficient use of material.
8. Low VOC or water-based interior paints are used at the interior of the building.
9. Raised-heel trusses use material efficiently and provide extra height for additional insulation.
10. Long-lasting standing seam metal roof will not require periodic or expensive re-roofing, and facilitates water catchment and recycling.
11. Three and a half inches of formaldehyde-free fiberglass insulation at the ceiling of the first floor and sound-absorbing Gypcrete at the second level subfloor block sound between floors.

Mechanical and Plumbing
12. Ten solar thermal panels at the roof and a 300-gallon storage tank provide pre-heated water for two on-demand hot water heaters.
13. Zehnder HRV (Heat Recovery Ventilator) extracts heat from bath air. Drain water heat recovery system extracts heat from upstairs shower water.
14. Supplemental heat (in addition to lighting, appliances and people) is provided by electrical towel warmers in baths, and inline gas duct heaters as a backup for the very coldest days. No conventional heating systems - furnace or radiant floors - are used or necessary.
15. Single-flush Stealth toilets use a maximum of .8 gallons per use.
16. A 5,000 gallon rainwater catchment system provides water for toilets, covering about 70% of projected use.
17. The building is pre-plumbed for a grey-water system.
18. Energy Star under-counter refrigerators are used.

Passive House Certification
19. For certification as a "Quality Approved Passive House," this building will be analyzed for its Specific Space Heating Demand (measured in kilowatt hours per area), Entire Specific Primary Energy Demand (measured in kilowatt hours per area including domestic electrical use), and a physical testing of air tightness using a blower and independent testing service, with a limit in air loss over an hour.

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