The next planning step in almost every window study is to evaluate
the condition of the windows by undertaking a detailed survey.
Peeling paint, broken glass, loosely fitted windows, and apparent
sill rot are not necessarily solid evidence that windows are
beyond repair. For a majority of older buildings, failure to
examine the existing window conditions closely precludes an
objective evaluation of repairing and upgrading the existing
windows versus partial or total replacing.
The surveys are often conducted by a window consultant, although
some architectural firms have benefitted by having a staff member
develop the skills to perform the survey. Without an objective
and detailed condition survey (along with the window assessment)
it is difficult to weight accurately the rehabilitation alternatives
to ensure that the most appropriate window treatment is chosen.
Too often the contractor is expected to give repair and replacement
costs with little guidance from the architect. There are inherent
problems in such an approach. Most contractors will not examine
the windows carefully because it is a time-consuming process,
and instead will bid close to replacement cost for repair work.
Replacing windows admittedly is easier to plan and budget for,
but in the final analysis it is not necessarily most cost-effective
If the window condition survey and the window significance
assessment clearly support retention of the historic windows,
then the next planning step is to examine the numerous options
for repairing and upgrading the existing units. Often the assessment
will prove inconclusive, thus requiring examination of other
alternatives, including replacing many or all of the windows
with others offering matching features and enhanced performance.
Based on the window assessment, there may be cases where replacement
windows could appropriately match only the overall appearance
of the historic window rather than the exact design. This makes
possible the use of modern commercial windows that have been
adapted to the historic rehabilitation market, yet that consist
of different materials. Once the options are identified and
preliminary cost estimates are derived, other factors may influence
final decisions about window work.
An energy study of the overall building — not just the
windows — coupled with cost-payback analysis may lead
to the conclusion that, for a particular building, double glazing
(retrofitted either to existing windows or in replacement units)
is simply not cost- effective. Such findings are not necessarily
confined to geographic areas with mild climates. Taking steps
to reduce air infiltration, however, is usually always cost-effective
where older, poorly maintained windows are involved.
Fisher, Chuck. Rehabilitating
Windows in Historic Buildings: An Overview (GSA 08500-03),
Preservation Technical Procedures, U.S.
General Services Administration