Portola Valley Town Center
The design of this Town Center redeveloped 11 acres of a surplus public school site into a park, play fields, and three primary Town Center structures – a Library, Community Hall, and Town Hall offices. The original structures on the site were astride the San Andreas fault, which forced their abandonment. The new buildings are arranged around a Town Plaza that terminates a sweep of reintroduced native and pastoral landscape. The Library contains reading rooms, a children’s area, staff office and the Town Heritage room. The Town Hall houses the administrative offices, Building, Planning, and Engineering departments as well as the town’s emergency operations center. The Community Hall provides a large divisible multi-purpose room, two activity rooms, storage and a catering kitchen. The Type V, wood frame buildings, are B-2 occupancy with accessory A occupancies. The $15 million dollar project was finished in October, 2008.
The old town center inhabited a 1950s school that was built directly on top of the San Andreas Fault. The new center occupies the same 11—acre site but locates the buildings in the northwest corner, out of the fault zone. While resolving the seismic, access, capacity, and infrastructure issues of the old town center, the new complex creates a unified place that supports the civic, community, and cultural life of the town and expresses the character and values of the town.
The town was founded in 1964 to protect the western hills from development, so it followed that the primary development goals for the new center were to increase open space, restore habitat, and create buildings that complement the natural landscape. The site plan—the result of many meetings and design workshops with town residents and staff—places the main buildings and town plaza in a corner of the site surrounded by tall trees. A wide swath of restored native landscape extends across the front of the site, through a meadow and a newly daylit portion of the creek and into the town plaza. Where the school buildings once stood, new playing fields open up to views of the western hills.
The three main town center buildings—the library, town hall, and community hall—are arranged around a town plaza and performance lawn. Reclaimed vertical redwood cladding links the buildings to the two large redwood groves on the site. Wide gabled roofs that present simple, familiar shapes visible from the road lift up inside the plaza to mark the entries and invite people in. Deep sheltering porches and sunscreens of reclaimed Alaskan yellow cedar shade the tall windows that look out to the landscape.
The old school buildings were deconstructed: the wood was remilled into paneling and ceilings for the new buildings, and —the concrete and asphalt was ground up and used as base rock. Local eucalyptus trees, cleared for fire prevention, were turned into flooring in the multipurpose room, and the alder trees cut down to make way for the new softball field became columns inside the buildings. The high-slag concrete keeps 100 tons of carbon dioxide out of the atmosphere. The town even has plans to turn the creek’s abandoned 60-inch concrete culvert into a rainwater cistern to collect and store run-off from the roofs for use in the landscaping.
Passive design strategies include natural ventilation, daylighting, thermal mass, and exterior shading. Efficient mechanical systems include radiant heat and nighttime cooling to keep energy use to a minimum. Three of the five buildings have roof-mounted photovoltaic panels that generate a total of 76 KW of on-site power. The site-generated power, coupled with the efficient design, results in buildings that use 53% less energy than Title 24 compliant buildings.
Narrative for “Saving By Design” Awards
The goal was to create, simple, low energy, climate responsive buildings, with a significant portion of their power supplied by site generated solar electricity. The buildings are designed to achieve all ten energy points in LEED Credit EA1. In addition to efficient heating, cooling and lighting systems, and a 76 kW photovoltaic system, the buildings incorporate a number of passive strategies.
The buildings are wood frame buildings, insulated with dense-pack cellulose insulation. The ground coupled slabs provide thermal mass and the Library and Town Hall Buildings have concrete stem walls for additional thermal mass to help keep the buildings at an even, comfortable temperature. Double hung, metal clad wood windows are glazed with a high performance glass (Tvis .66, SHGC .25, Shading Coefficient .24.) South and west windows are shaded with fixed wooden sunscreens. Daylighting strategies include tall windows, clerestories, and light colored ceilings and achieve a glazing factor of 2% in 98% of the regularly occupied spaces. The metal standing seam roofs have a Solar Reflectance Index of .29.
Hydronic radiant floors provide heat for the Library and Town Hall, the Community Hall, with it’s less frequent use and higher occupant loads, utilizes two forced air gas furnaces. The boilers for the hydronic heating systems are small, high efficiency boilers. All of the air handlers are equipped with heat recovery units to recover heat from exhaust air.
Cooling and Ventilation
Cooling for the buildings is a combination of passive and active sources. The main source of cooling and ventilation is operable windows and high clerestories. A fan based nighttime purge cycle is used to cool the building’s thermal mass at night. Ceiling fans provide additional comfort on hot days. All of these strategies will provide excellent comfort on all but the hottest days. For the those hot days, small, high efficiency (SEER 19) compressor based, direct expansion cooling systems are used to pre-chill the make up ventilation air. Natural ventilation is supplemented by the air handlers and cooling unit. On cold days, hot water from the hydronic boilers is supplied to the air handlers through a hot water coil in the front of the units.
The Photovoltaic panels mounted on the roofs of the Library, Community Hall and an independent array on the maintenance building produce a combined output of 76 kW. The arrays on the Library and Community Hall produce a total of 70 kW of power for the Town Center buildings or roughly 26.66.% of the electric energy requirements of the Town Center buildings. There is also a small 6 kW system on the maintenance buildings. We estimate the PV systems save 31 tons of CO2 a year.
The energy models show a 53.5% reduction in energy costs for the three main buildings.
Title 24 Calculations for the three main town center buildings are attached.
765 Portola Road
Portola Valley, CA 94028
1295 59th Street
Emeryville, CA 94608
Goring & Straja Architects
5701 Hollis Street
Emeryville, CA 94608
99 Linden Street,
Oakland, CA 94607
510-663-2070 Ext. 201
2815 18th Street,
San Francisco, CA 94110
415-920-2800 Ext. 104
TBI Construction & Construction Management
1960 The Alameda, Suite 20
San Jose, CA 95126
William E. Fee