Setting goals for a successful window replacement involves considerations for aesthetics, cost, schedule, view, and a variety of performance characteristics. The process becomes more complicated when dealing with historical projects.

There is a broad range of historic building types and levels of rigor in restoration, from the downtown office building whose ornamental façade may enhance its appeal to potential tenants, to sites listed in the National Register of Historic Places.

Needs for easy customization and durability have made aluminum an important material choice for historically influenced window replacement work. Factory-applied eco-friendly anodize and baked-on fluropolymer paint finishes offer long-lasting options to match existing hue schemes, exacting palettes, or a return to original colors, after years of chalking, peeling, or expensive repainting.

Product Selection

In many historically influenced replacement projects, the windows being replaced are tall, double-hung, sash used for natural daylighting in buildings constructed before the advent of efficient, artificial lighting.

When upgraded from single glazing to insulating glass, these tall, hung sashes get quite heavy, often making replacement double-hung windows difficult to operate, and prone to premature wear of counter-balancing mechanisms.

Simulated Double Hung Window

Projected windows offer an easy-to-operate alternative. These vent types are compression sealed, low air infiltration does not require high operating force, and smooth-operating cam locks, keepers, friction hinges, or butt hinges are long-lived. Wausau's 4250i INvent^TM Simulated Double Hung can even offer the 'offset' glass plane appearance of hung sash, with optional between-glass blinds for privacy and control of solar heat gain.

Wausau offers a 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 products, including Wausau's popular 2250-E Epic^TM and 3250-H Heritage^TM series, are available with matching beveled muntin grids.

Wausau's Energy Modeling Tool provides comparative building energy performance - annual energy use, peak demand, carbon emissions, daylight, glare, and condensation - to optimize product selection. Developed by the University of Minnesota Center for Sustainable Building Research, simulations use COMFEN from

Lawrence Berkeley National Labs' Windows and Daylighting Group.

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, and thermal comfort LEED points, as well as daylight and views.

Panning Versus Tear-Out

The key logistical decision faced by the window replacement contractor is whether to leave existing window frames in place, or do a complete 'tear-out' and start again.

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Removal of existing operable sash, while leaving existing window framing in place, usually makes for a much faster installation process, and minimizes disruption to occupants. The existing frames are used as anchorage points, and an extruded aluminum sub-frame or 'panning' system lines the opening.

The cavity between the window frame and panning should always be insulated to avoid extraneous heat loss or heat gain. It is particularly important to pay attention to the continuity of vapor retarders at existing perimeter conditions.

If a tear-out of existing frames is the path chosen, perimeter protection is often required in occupied spaces and the process considerably slows. Caution must be exercised in determining what concealed wall materials may be disturbed.

For major renovation projects, installation of in-situ samples is highly recommended.

Wausau S.E.A.L. Windows  

When existing windows are weather-tight, and operation for ventilation is not a requirement, the addition of high-quality, custodian-operable, interior accessory 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 window undisturbed.

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