Green Goals
Preserving or increasing daylighting is a key consideration in window system renovations. Its benefits are recognized and promoted through green building programs such as the Washington, D.C.-based U.S. Green Building Council’s LEED system. Natural daylighting in architecture seemed to be a lost art for many years. Tall, triple-hung windows, clerestory and skylight glazing and courtyard areas characterized turn-of-the-century institutional buildings. Those features maximized natural daylight penetration by necessity—available artificial lighting was insufficient to allow effective use of many spaces during low-light periods.
Those design features seldom were seen in more compact floor plate designs popularized after the advent of inexpensive artificial lighting, but they are making a major comeback as the increasing cost and environmental impact of wasted energy is emphasized. Addressing this, LEED’s Energy and Atmosphere credits are based on the Washington-based U.S. Department of Energy’s Energy Star for Buildings methodology.
Energy Star is earned by comparing a building’s energy consumption with other buildings of similar size and energy use. More than 4,000 buildings nationwide have placed in the 75th percentile or higher, earning Energy Star recognition. LEED-EB starts at the 60th percentile prerequisite, and requires 99th percentile performance to earn all 10 LEED points.
Energy-efficient, historically accurate replacement windows can play an important role in improving older buildings’ performance and in achieving these designations. Many window manufacturers are capable of preparing analyses to quantify energy savings. The DOE and Lawrence Berkeley Laboratory’s publicly available software tools, RESFEN and COMFEN, can be readily adapted to compare energy costs related to existing windows with those to be expected with new windows, while also providing valuable information about glare and HVAC capacity reductions.
Today, dozens of historic properties have their own payback models and green programs. Committed to environmentally responsible design, Pittsburgh’s Carnegie Mellon University seeks LEED certification for nearly all of its construction projects. Its expansion to the historic Henderson House student residence earned the campus its second LEED-Silver certification. The residence’s windows preserve the original structure’s traditional architectural features and complement its fieldstone walls. In addition to matching Carnegie Mellon’s classic collegiate styling, these windows significantly upgraded the old steel frame, single pane units’ performance while staying within budget and on schedule.
Vintage Styling
Most national aluminum window manufacturers offer a broad range of operating window types with beveled exterior glazing rebates, replicating the look and texture of old existing putty-glazed steel, bronze or wood sash. These are available with matching beveled muntin grids (see sidebar “Muntin Grids”, page 4).