DOE study shows window retrofit system slashes energy use at northeastern mid-rise

Energy Savings in 40-Year-Old Landmark Exceeding Pre-Renovation Projections

400 Market Street, a 12-story building in Philadelphia with a revolutionary window retrofit system, was selected to be part of a U.S. Department of Energy (DOE) project as a blueprint for turning drafty old buildings with single pane windows into national models of energy efficiency. After just a few months of testing, it is becoming increasingly clear that the agency’s choice was a good one.

Built in 1972, 400 Market Street is a 200,000-square-foot mid-rise that fits the profile of hundreds of 30- to 60-year-old buildings across North America that need to be reglazed for aesthetic, comfort, environmental and practical reasons. Last year, it was selected to be part of a $1.6M DOE-funded project with J.E. Berkowitz LP, Quanta Technologies Inc., and NAHB Research Center to demonstrate the ability of low-e retrofit glazing systems to significantly improve the energy efficiency of older commercial and residential buildings. Using sophisticated energy modeling software provided by the DOE before the renovation, J.E. Berkowitz estimated that the retrofit would reduce annual energy costs at 400 Market Street by $55,000. The first results since the project was completed show the building outperforming the projection.

“While our study has just started, preliminary observations are very encouraging,” said Thomas Culp, manager of the DOE project. “In November and early December, the east-facing offices showed about a 27 percent reduction in heating and cooling energy use, and the north-facing offices showed more than a 50 percent reduction. I will be very interested in seeing the continued results through the full winter.”

After researching various window retrofit strategies, the owners of 400 Market Street chose RENOVATE BY BERKOWITZ (RbB), a revolutionary on-site window retrofitting system developed by local glass fabricator J.E. Berkowitz, LP, that converts existing single-pane windows into energy-saving, triple-glazed insulating glass units (IGUs), while preserving a building’s exterior. 

“A lot of attention is given to new windows and buildings, while ignoring the vast amount of energy being wasted in older buildings with single glazing,” says Culp. “400 Market Street is the first of multiple case studies of the RbB system in commercial buildings to determine year-round energy savings and other benefits.”

The NAHB Research Center is monitoring indoor conditions and energy consumption. While the utility usage of the entire building is being examined, the main technical analysis is from isolating and monitoring energy use in two pairs of unoccupied offices facing different directions—north and east. Within each pair, one room has been retrofitted with RbB while its twin will be left with no renovation until the end of year-long study.For more information about how the RbB system is helping 400 Market Street save thousands of dollars in energy, labor and related costs, call (800) 257-7827 or visit About JEB

JE Berkowitz, LP is a leading architectural glass fabricator. Founded in 1920, the ISO 9001 certified company serves customers for the domestic and overseas architectural markets. Products include Tempered Glass, Insulating Glass, Spandrel Glass, Silk-Screened Glass, Glass Doors and Entrances, Laminated Glass, and Point Supported Canopy and Wall Systems. The family-owned glass business is located in Pedricktown,, N.J., with over 200,000 square feet of plant space and over 200 employees. For more information, visit