What Replacement Windows Can’t Replace:
The Real Cost of Removing Historic Windows
WALTER SEDOVIC and JILL H. GOTTHELF
Sustainability looks even better
through a restored window.
in this case, windows — without fully
evaluating the consequences. Once au-thentic
material is lost, it is lost forever.
It does not matter how accurate the re-placement
window, it never reflects the
nuances of the original.
Taking the Long View
Historic windows possess aesthetic and
material attributes that simply cannot
be replaced by modern replacement
windows. Like preserving whole build-ings,
restoring historic windows is a
solid step forward into the realm of
sustainability. The present approach to
sustainability, however, still too often
focuses on new construction and issues
such as “intelligent” windows and
energy efficiency, while overlooking
other important, holistic benefits of
preserving historic windows, such as
the following:
• Conservation of embodied energy
(i.e., the sum total of the energy
required to extract raw materials,
manufacture, transport, and install
building products). Preserving his-toric
windows not only conserves
their embodied energy, it also elimi-nates
the need to spend energy on
replacement windows. Aluminum
and vinyl — the materials used in
many replacement windows — and
new glass itself possess levels of em-bodied
energy that are among the
highest of most building materials
(Fig. 1).2
• Reduction of environmental costs.
Reusing historic windows reduces
environmental costs by eliminating
the need for removal and disposal of
existing units, as well as manufacture
and transportation of new units.
Also, many replacement units are
manufactured with such materials as
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For all the brilliance reflected in efforts
to preserve historic buildings in the U.S.,
the issue of replacing windows rather
than restoring them remains singularly
unresolved. Proponents on both sides of
the issue may easily become frustrated
by a dearth of useful data, as well as
conflicting information, or misinforma-tion,
promulgated by manufacturers.
Indeed, it often seems that many preser-vation
practitioners and building own-ers
remain in the sway of advertising
claiming that the first order of business
is to replace old windows. In the con-text
of preservation and sustainability,
however, it is well worth reconsidering
this approach.
Sustainability and Authenticity
In considering alternatives to replacing
historic windows, one needs to keep in
mind two important elements: sustain-ability
and authenticity. Sustainability
(building green) and historic preserva-tion
are a natural marriage, so long as
one remains mindful that sustainability
is not just about energy conservation.1
Preservation and sustainability involve
myriad elements that can work in sym-biotic
and synchronized ways toward a
favorable outcome. For example, pres-ervation
work is more labor- than
material-intensive, which benefits local
economies; natural ventilation afforded
via operable windows can reduce the
size of mechanical equipment, especially
of air-conditioning; and salvaging his-toric
materials, such as wood sash,
obviates the need to harvest live trees
and other natural resources for the
manufacture of replacement units.
Similarly, retaining and celebrating
authenticity is one key element of an
exemplary preservation program. No
one should take lightly the option of
discarding authentic historic materials —
Fig. 1. Comparative values of the embodied-energy
levels of common building materials.
Note that glass and aluminum (i.e., principal
components of many replacement windows)
are ranked among the highest levels of embod-ied
energy, while most historic materials tend to
possess much lower levels. Courtesy of Ted
Kesik, Canadian Architect’s Architectural Sci-ence
Forum, Perspectives on Sustainability.
