K-12 Schools

7 Keys to Unlocking Energy Efficiency in Schools

Aug. 11, 2010
3 min read

 

 For two elementary schools in Snohomish, Wash., the design team from NAC|Architecture and Hargis Engineers developed energy-saving strategies for foundations, roofs, walls, and windows in order to be able to reduce the size and cost of the mechanical systems. The chart shows the relative energy loss for each major component after enhancements were made. Windows and doors account for 75% of loss. Axonometric representation of the enhanced wall in two Snohomish, Wash., schools. In the rainscreen cavity, one inch of polyiso rigid insulation (R-6.7) is used where the exterior cladding is masonry veneer. The International Building Code restricts the use of foam plastic, particularly in multistory noncombustible construction, so careful attention to code requirements is needed when selecting spray foam or rigid insulation products. Where the cladding is fi ber-cement panels, metal siding, or other thin material, two inches of mineral wool semi-rigid boards (R-4.2
per inch; R-8.4 total) were used. When this is added to the six inches of spray foam in the stud framing cavity, the composite insulation value of the overall wall assembly is R-25.

1. Building envelope – Wrap it tightly

Energy efficiency in schools, as in virtually all buildings, begins with a well-insulated building envelope. Combined with a properly designed and maintained ventilation system to draw in fresh outside air, creating a tight envelope is the first step in the march toward energy efficiency.

Exemplifying good building envelope design principles are the Riverside and Machias elementary schools (each at 72,000 sf). Designed by NAC|Architecture, Seattle, the schools are currently under construction and will replace two older structures that were among the least energy-efficient in the Snohomish (Wash.) School District.

“We focused on how an enhanced envelope design could reduce the size and cost of the mechanical systems by reducing energy loss through the envelope,” says Philip Riedel, associate principal with NAC|Architecture. A key component of that strategy is a six-inch layer of closed-cell polyurethane foam insulation in lieu of batt insulation in the walls.

The foam yields an R-value of 6.7 per inch, a substantially higher insulation value than batt at that thickness, although it does comes at a significant initial cost premium—about 20% more than an equal R-value of rigid insulation. “However, we are finding that a 1% overall gap between rigid insulation boards can reduce energy efficiency by 10%,” he says. “Since the spray-on insulation eliminates seams, the payback is nearly immediate.”

NAC also took measures to mitigate the effects of thermal bridges due to metal studs and the concrete slab. By increasing stud spacing from 16 inches on center to 24 inches, the design increases the effective wall R-value from R-7.1 to R-8.6, a 21% improvement, NAC says.

In conventional foundation construction with insulation adjacent to the interior of the stem wall and below the perimeter of the slab, heat travels from the warm concrete slab out through the concrete stem wall. “We ran rigid insulation up to the top of the slab, creating a full thermal break at the perimeter,” Riedel says. “These thermal breaks provide smaller contributions to envelope efficiency than the spray foam insulation and the triple-pane glass used in all windows and curtain walls, but we wanted to take every advantage we could.”

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