QUALIFYING FOR SILVER STATUS
In 2004, Lexington's Board of Selectmen approved a policy requiring all new public buildings to be designed and built to meet LEED Silver guidelines.
Three years later, residents voted to fund construction of a new, $25.5 million building by approving a referendum (a debt exclusion override) authorizing the financing of the project outside the limits of a state statute that limits property tax increases. Last year, the tax impact on a $729,000 single-family home was $212, a figure that decreases each year over the bond's 20-year term.
With funding ensured, the town contracted HKT Architects to design the building, in part because the firm had two LEED-certified buildings and multiple public facilities under its belt.
HKT used LEED standards as a guide for incorporating the U.S. Green Building Council's (USGBC) six aspects of sustainability:
Sustainable sites. The top of the facility is a “cool roof” that minimizes the potential for creating an urban heat island.
A green roof over the central storage area keeps the space below warmer in winter and cooler in summer while filtering stormwater runoff from that portion of the roof.
The rest of the roof has a solar reflectance index (SRI) rating of 79. The standard black roof on the typical commercial facility is 0. This “high-reflectance” rate was achieved by specifying a “white roof” system that reflects rather than absorbs sunlight and heat as black roofs do.
The system consists of a steel deck overlaid with polyisocyanurate insulation and a modified bitumen membrane called Ruberoid EnergyCap SBS 30 FR, which is made by GAF Materials Corp. In addition to being white, the membrane meets LEED SRI requirements.
Although it looks flat, the roof tilts very slightly so rain can be collected and reused. Under LEED Sustainable Sites Credit 7.2, the roof is “low slope,” which means it has a slope of less than or equal to 2 inches of slope per 12 inches of rise (2:12).
Stormwater runoff from the white roof is estimated to be 29,052 cubic feet in a 100-year rain event. Therefore, underground infiltration chambers that capture up to 29,200 cubic feet were installed. Rain flows from the roof to the chambers and infiltrates into the ground over time.
Bio-retention and constructed wet-lands also control and treat runoff.
Water efficiency. To reduce potable water consumption, the facility is equipped with low-flow plumbing fixtures and dual-flush toilets.
Rain flowing from the vehicle staging area's roof is stored in 500-gallon tanks installed in 10 locations throughout the site. The 5,000 gallons of “harvested” water fill street sweepers and vac-trucks and supplement the wash bay.
Energy and atmosphere. At the front of the facility, where offices and conference rooms are located, the wall system has almost three times the insulation value of the state's energy code at the time of construction. The rest of the facility has almost two times the insulation value.
In administration areas, HKT specified 2½ inches of rigid insulation with an R-value of 12.5, along with The Dow Chemical Co.'s 1-inch Thermax insulating exterior sheathing with a 6.5 R-value. The same rigid insulation, minus the exterior sheathing, was installed in the minimally heated operations areas: central storage, maintenance, shops, vehicle storage, and wash bay. In those areas, noninsulated exterior sheathing was used instead.
Based on energy modeling performed during the design phase, public works should recoup its investment in higher-than-required insulation values within seven years, according to HKT Project Manager Michael Lawrence.
Lighting and air circulation in the operations areas presented two opportunities to sustainably economize. The areas are enclosed with polycarbonate clerestory, an inexpensive alternative to glass that reduces the need for artificial light during the day. Gravity vents cool the interior spaces while dissipating any carbon monoxide generated from fleet operations, enhancing employee safety.
The maintenance bay's doors face south to make the most of the sun's rays for heat and light during the winter. A canopy above the doors keeps the sun's rays out during the summer.
Large windows throughout all occupied spaces provide natural daylighting, reducing the need for artificial lighting. Employees in office areas and conference and meeting rooms can open and close them as needed, further reducing mechanical heating and cooling requirements.
Materials and resources. Eighty-five percent of the old building, as well as construction waste, was reused or recycled. For example, the old facility's asphalt pavement was ground up onsite and used as structural fill under the new building.
Seventy-five percent of all new building material was extracted, harvested, or manufactured within 500 miles of the project.
SAMUEL HADLEY PUBLIC SERVICES BUILDING
Project delivery method:
CTA Construction Inc., Boston
HKT Architects Inc., Somerville, Mass.
Design and construction:
82,100 square feet
16,900 square feet
41,100 square feet
Maintenance area and wash bay:
11,500 square feet
Central storage and shops:
9,200 square feet
3,400 square feet
11,300 square feet
U.S. Green Building Council's
LEED Silver certification