Help Your Office Building Compete
|An efficient fenestration system appeals to tenants and saves on operating costs.|
Help Your Office Building Compete
Energy-efficient fenestration in an office building attracts satisfied tenants.
Rich Walker, American Architectural Manufacturer
As the construction deep-freeze thaws, as it eventually will, the competitive environment will make it more important than ever for new or remodeled commercial buildings to attract investors and prospective tenants. Determining the optimum combination of building performance and functionality to achieve such appeal depends heavily upon the building’s fenestration system, which involves careful attention to a number of design considerations. Many of these are of greater concern and consequence for commercial projects than for residential applications.
Today, green credentials demonstrably move projects to the top of the desirability pecking order. The 2008 Green Building Survey, conducted by National Real Estate Investor, New York, states that corporate respondents are willing to pay an average of 4% more for LEED-certified buildings; developer respondents say they can charge an average of 3% higher rents for green properties. This fact is not lost on developers and owners. According to New York-based Turner Construction Co.’s Green Building Barometer, 75% of commercial real estate developers, rental building owners, brokers, and others say the credit crunch will not discourage them from building green. A full 84% of respondents said their green buildings have resulted in lower energy costs, with 68% reporting lower overall operating costs.
For these reasons, green building is one of the growing bright spots for the U.S. economy. Verifying the trend, New York-based McGraw-Hill Construction’s Green Outlook 2009 report states that the value of green building construction starts increased five-fold from 2005 to 2008 and could triple by 2013.
For fenestration products, green building encompasses a variety of design considerations. Energy efficiency is the key element, together with beneficial daylighting to supplant electric lighting, and an emphasis on products with minimal environmental impact throughout their lifecycles.
The building’s location determines outdoor design temperatures (winter lows and summer highs), which dictate the windows’ required level of heat-transfer coefficient (measured by U-value), as well as solar heat gain (measured by the solar heat gain coefficient, or SHGC). Because energy use in commercial buildings is typically dominated by cooling loads, a lower SHGC is often desirable. However, buildings in northern climes can benefit from higher SHGCs as a means to offset thermal transmittance losses. These values are optimized as needed by the use of insulating glass units (IGU) with inert gas infill, and warm edge spacers separating the inner and outer lites (panes), framing with inherent or engineered integral thermal barriers, and glass with special coatings such as reflective glazing or high-performance low-e coatings.
AAMA (American Architectural Manufacturers Association, Schaumburg, IL) is developing a point-system-based green certification program for scoring the green credentials of window and door products. The program is intended to help designers and specifiers select products that will maximally contribute to whole-building green rating systems such as the LEED program, and the Green Globes assessment and rating system for commercial buildings.
Windows must meet certain basic requirements for structural performance. The International Building Code (IBC) requires that windows meet the performance requirements of AAMA/WDMA/CSA 101/I.S.2/A440-08, NAFS-North American Fenestration Standard/Specification for Windows, Doors, and Skylights or a referenced predecessor. These standards define minimum structural performance requirements, as well as the window’s ability to resist air infiltration and water penetration due to wind-driven rain. For a product to gain entry to one of these performance classes, it must be tested to withstand progressively higher minimum design pressures derived from the maximum wind velocity likely to be experienced at a given geographical location. Several different performance classes are defined by their minimum design pressure, water penetration resistance, and air-leakage resistance requirements and identified according to their typical application: R, LC, CW, and AW. Windows for most office buildings, particularly multi-story ones, are likely to fall within the CW or AW classes.
Studies indicate that office productivity increases when intrusive racket-from traffic, airplanes, mass transit systems, and other outside noise-is reduced. For noisy urban environments, products identified as acoustic windows should be chosen and tested for sound-transmission loss, and assigned a sound-transmission class (STC) and an outdoor-indoor transmission class (OITC). The higher these indices, the better.
Design features that improve sound control include, but are not limited to, double glazing (insulating glass units) with asymmetrical glass thickness, maximizing the space between the lites, laminated glass (the plastic interlayer dampens vibrational energy), soft resilient seals and weatherstripping (such as neoprene gaskets), and robust framing that resists vibration. (Editor’s note: For more detail, see our June 2008 issue, page 20, concerning acoustic performance for school windows.)
Safety and security
In locations where safety and security are key concerns, windows should be selected for the degree of forced entry resistance (FER) that they offer, which is accomplished by using the proper combination of hardware (locks and hinges) and glazing. The suite of standards AAMA 1302, 1303, and 1304 set guidelines for testing and rating of products that can mitigate break-ins and vandalism.
A more recent safety concern involves the ability of a window to resist an explosive blast and prevent flying glass shards. Blast-resistant products, typically with laminated glass and reinforced framing, can be rated and compared for blast resistance using AAMA 510-06, Voluntary Guide Specification for Blast Hazard Mitigation for Fenestration Systems.
Another consideration for windows used in office buildings is the ease of upkeep and care. Ideally, windows should be easy to keep clean and deliver a long, trouble-free service life, characterized by insulating glass seals that resist failure or deterioration of the finish. Ease of maintenance depends on the window type, simplicity of re-glazing in the event of replacement, and ease of access for cleaning.
Real world windows
Examples of how window and door design achieves an optimal balance among the various design considerations include the following:
When Marathon Oil undertook a renovation of its Findlay, OH, headquarters for refining, marketing and transportation, the focus was on windows. The objective was to maximize energy efficiency while closely matching the historical look of the existing window system. A dual-finish aluminum window with advanced-engineered, thermal-performance characteristics was the answer. The thermal barrier is built using a composition of glass-reinforced nylon, while non-metallic, warm-edge IGU spacers provide high-performance heat insulation.
Sacramento, CA’s 1.1 million-sq.-ft. Capitol Area East End Complex, the largest office project ever undertaken by the State of California Dept. of General Services, had to meet or exceed California Building Code Title 24 for energy efficiency and green buildings. Strategies included integrating energy-efficient glass into the building’s faade to maximize the use of daylight. Spectrally selective, low-e glass allows most of the visible light to penetrate the building, while blocking nearly all of the unwanted warmth generated by infrared wavelengths.
Wisconsin’s Dane County Justice Center, Madison, is the first facility to meet the county’s new green-building guidelines, which are equivalent to those meeting a LEED Silver rating. The building features a high-performance, zero-sightline curtain wall and integrated operable window systems with low-e glazing to provide ventilation and maximize daylighting. It is estimated that the building will save as much as 50% in electric consumption, and 37% in overall annual operating energy, amounting to a payback of 4.8 yr.
With performance and operating costs paramount among the criteria by which office buildings are judged by investors and tenants, it is essential that a well-reasoned balance be struck among the various constraints imposed by the function of the building and its location. The design and selection of fenestration products have a major influence on the outcome, and current standards and technologies offer useful guidance.