Hung windows operate by sliding vertically in the plane of the wall. This operating mode can be convenient when interference with window coverings or walking surfaces immediately adjacent to windows is undesirable. Of course, in many historical window replacement projects, the windows being replaced are tall, double- or triple-hung sash used for natural daylighting in buildings and were constructed before the advent of efficient, artificial lighting.
When upgraded from single-glazing to double or triple insulating glass, these tall, hung sash get quite heavy. The need to reduce air infiltration, noise and drafts makes it logical for sliding weather-strip to fit tighter in new windows. The combination of large sash size, heavier insulating glass and tight air seals may make replacement double-hung windows difficult to operate, even with modern balance technology. Lift assistance varies from 30 percent to 70 percent depending on balance type, but longevity of these heavy-use hardware components can be an issue, leading to yet another replacement.
Projected windows offer an easy-to-operate alternative. As the name implies, projected windows operate by projecting inward or outward from the plane of the wall, as casements, awnings or hopper vents. Because 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. Limited opening devices prevent excessive projection into adjacent areas. Projected windows also can be engineered to simulate the offset glass plane appearance of hung sash.
The Department of Veterans Affairs’ 1920s facility in Battle Creek, Mich., recently renovated Building 29 for energy efficiency and patient safety. Along with needing high-performance, operable, psychiatric grade windows, the units also needed to reflect the original, architectural intent, explains Jeff Vliek, who served as the project’s team leader for glazing contractor Battle Creek Glass Works Inc., Battle Creek.
Preserving the historic profile, applied muntins on the windows’ exterior contribute to the original, multi-pane appearance and invite natural light into every room. The VA’s staff controls the windows’ operation. For safety, concealed hinges and tamper-resistant locks secure the opening during normal operating conditions. The windows remain closed throughout Michigan’s freezing, winter months, keeping patients as comfortable as possible inside.
Panning Versus Tear-out
The key logistical decision faced by the window replacement contractor on a historic property is whether to leave existing window frames in place, or do a complete tear-out and start again.
Removal of existing operable sash, while leaving existing 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.