High Performing Buildings - Spring 2008 - (Page 14) W AT E R C O N S E R VAT I O N Water conservation, a visible concern in the Northwest, provides another example of Seattle City Hall combining design elements and sustainable strategies. Water conservation contributes eight points toward LEED, more than any other building system. The rainwater harvest system alone achieved all five water efficiency points for LEED plus an innovation in design credit for exceeding performance levels. A garden roof planted over the lobby portion of the building reduces runoff by soaking up Seattle’s abundant rainwater, allowing it to evaporate gradually. Excess water is harvested in a 220,000 gallon rainwater cistern built in the basement of the demolished municipal building. Three pumps in the mechanical room deliver water to toilets and the landscape sprinkler system. Waterless urinals along with low flow automatic flush toilets and lavatory fixtures reduce overall water use. Landscape irrigation is a drip system with an automated controller connected to a soil moisture sensor for maximum efficiency. In an average year, the harvested rainwater will accommodate 100% of irrigation and toilet water. Precipitation managed on site Total water used indoors 83% 844,500 gallons per year 33,200 gallons per year The garden roof was bid as an alternate to the base bid for a conventional roof with concrete pavers. The alternate was $3/ft2 more than the base bid. When bids for other building elements came in below estimate, the city reallocated the money to include the green roof. In a native Puget Sound forest, 25% of the annual rainfall is evaporated or transpired. The garden roof over the main lobby of Seattle City Hall evaporates and transpires enough water to equate to one-third of this aspect of the native forest condition. Total water used outdoors Percent of total water from reclaimed sources Calculated annual potable water use 31% 3 gallons/ft2 per year oration between the design team and the subcontractor. Details were jointly developed that enabled the laminated glass panel to be offset from the vertical mullions. The back edge of each panel is supported by a stainless steel channel attached only to horizontal mullions. The design creates a syncopated rhythm across the façade. Decisions regarding the daylighting and solar control of the building were 14 HIGH PERFORMING based on the massing of the building and disposition of interior functions, tested by solar modeling early in design. Following the civic center master plan, the tower was placed on the north side of the block, maximizing sun on the plazas and public spaces that occupy the southern portion of the block. The resulting exposed south face of the office tower is backed by a single Spring 2008 public corridor. Elevators open on each floor facing the view to help orient visitors. By setting this transient space to a higher temperature setpoint, the corridor serves as a heat buffer for the office spaces. As noted previously, the fritted glass reduces heat gain without obstructing views. This increases building performance in a more cost-effective manner than the double glass wall that was ini- BUILDINGS
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