The General Services Administration (GSA) owns more than 400 buildings listed in, or eligible for, the National Register of Historic Places 
(NRHP). Similar to private sector projects, the GSA is required to use state historical preservation offices (SHPOs) to assess the potential adverse impacts per the U.S. Secretary of Interior's "Standards for Rehabilitation." For GSA-owned buildings, blast hazard mitigation and hurricane impact resistance can take precedence over preservation, however other historical renovation parameters still hold.
Historic Preservation Tax Credits
Significant tax credits are available for the preservation of historic buildings with private sector owners. The Tax Reform Acts of 1976 and 1996 incentivize historic rehabilitation, helping to defray the added cost of rigorous, historically accurate preservation.
There are two levels of tax credit:
- 20% for certified rehabilitation of a certified structure
- 10% for non-historic buildings pre-1936
The market has responded with amazing vigor - with nearly 30,000 buildings having qualified for the higher tax credit since its inception, driving investment of more than $20 billion. The program is administered jointly by the NPS, the Internal Revenue Service and the SHPOs nationwide.
To qualify for the maximum 20% tax credit, both the structure and the rehabilitation process must be certified. Certified structures are those that are either listed on the NRHP, or are more than 50 years old and contribute to the historic significance of a registered historic district. A certified rehabilitation process is one consistent with the historic character of the building or district as evidenced by the written review and approval of the SHPO and the NPS.
The most historically accurate windows are the original windows. However, they may have been replaced in later years, deteriorated to the point where they are not salvageable, or rendered un-useable by changes in building occupancy.
When replacement is required, and using the same material is not technically or economically feasible, the referenced standards still require preserving distinctive features, finishes and construction techniques, and call for matching design, color, texture and visual quality. Distinctive features include frames, sash, muntins, glazing, sills, heads, hoodmolds, paneled or decorated jambs and moldings, as well as interior and exterior shutters or blinds. The SHPOs have the last word in acceptability of replacement window aesthetics.
Energy codes and other provisions of the local building code may be different for historically significant buildings, and also may depend on the extent of the retrofit.
Green Building
Recognizing the environmental benefits of renovation, the U.S. Green Building Council's (USGBC) voluntary, consensus-based Leadership in Energy and Environmental Design rating system for New Construction and Major Renovations (LEED�-NC Version 3) awards points under Material and Resources (MR) Credit 1, Building Reuse.
LEED for Existing Buildings (LEED-EB) includes Energy and Atmosphere (EA) credits based on the U.S. Department of Energy's Energy Star for Buildings� methodology.
Energy-efficient, historically accurate replacement windows can play an important role in improving older buildings' performance and in achieving these designations, through energy savings, recycled content, regional extraction, increased ventilation, thermal comfort, daylight and views.
Interior Accessory Windows
When original windows are weather-tight, and operation for ventilation is not a requirement, the addition of high-quality, custodian-operable, Wausau S.E.A.L.™ Series windows can be a viable option. With appropriate caution to avoid between-glass condensation, these economical add-on units improve control of sound, energy, air and light, while leaving existing windows undisturbed.
For historical preservation, fenestration is the single most-notable architectural feature of many landmark structures, and when replacement is necessary, detailing warrants close attention. Contact Wausau for in-person presentation of the AIA CES program, "Historically Accurate Windows - Respectful Renovation."
Find us online at www.WausauWindow.com.
Email Wausau's Market Managers at [email protected], [email protected], [email protected]. 
Glassmaking technology in the years prior to World War II limited the size of individual glass lites, mitigating the use of putty-glazed muntin grids. Only TDL design can reproduce this aesthetic with the fidelity required for rigorous historical preservation. While often associated with Colonial, Gothic or Victorian architecture, TDL muntin grids were employed out of necessity in buildings of many styles, including Art Deco, Post-Modern and Industrial.