Repair of historic windows is always preferred within a rehabilitation
project. Replacement should be considered only as a last resort.
However, when the extent of deterioration or the unavailability
of replacement sections renders repair impossible, replacement
of the entire window may be justified.
This is a successsful replacement in kind of the deteriorated frame shown above. Photo: Henry Chambers, AIA. |
In the case of significant
windows, replacement in kind is essential in order to maintain
the historic character of the building. However, for less significant
windows, replacement with compatible new windows may be acceptable.
In selecting compatible replacement windows, the material, configuration,
color, operability, number and size of panes, profile and proportion
of metal sections, and reflective quality of the original glass
should be duplicated as closely as possible.
A number of metal window manufacturing companies produce rolled
steel windows. While stock modern window designs do not share
the multi-pane configuration of historic windows, most of these
manufacturers can reproduce the historic configuration if requested,
and the cost is not excessive for large orders. Some manufacturers still carry the standard pre-World
War II multi-light windows using the traditional 12" x 18"
or 14" x 20" glass sizes in industrial, commercial,
security, and residential configurations. In addition, many of
the modern steel windows have integral weatherstripping, thermal
break construction, durable vinyl coatings, insulating glass,
and other desirable features.
Windows manufactured from other materials generally cannot match
the thin profiles of the rolled steel sections. Aluminum, for
example, is three times weaker than steel and must be extruded
into a boxlike configuration that does not reflect the thin historic
profiles of most steel windows. Wooden and vinyl replacement windows
generally are not fabricated in the industrial style, nor can
they reproduce the thin profiles of the rolled steel sections,
and consequently are generally not acceptable replacements.
For product information on replacement windows, the owner, architect,
or contractor should consult manufacturers' catalogues, building
trade journals, or the Steel Window Institute, 1230 Keith Building,
Cleveland, Ohio 44115.
The National Park Service recommends the retention of significant
historic metal windows whenever possible. Such windows, which
can be a character-defining feature of a historic building, are
too often replaced with inappropriate units that impair rather
than complement the overall historic appearance. The repair and
thermal upgrading of historic steel windows is more practicable
than most people realize. Repaired and properly maintained metal
windows have greatly extended service lives. They can be made
energy efficient while maintaining their contribution to the historic
character of the building.
NOTES
(1) The technical information given in this brief is intended
for most ferrous (or magnetic) metals, particularly rolled steel.
While stainless steel is a ferrous metal, the cleaning and repair
techniques outlined here must not be used on it as the finish
will be damaged. For information on cleaning stainless steel and
nonferrous metals, such as bronze, Monel, or aluminum, refer to
Metals in America's Historic Buildings (see bibliography).
(2) Refer to Table IV. Types of Paint Used for Painting Metal
in Metals in America's Historic Buildings, p. 139. (See bibliography).
(3) One measure of energy efficiency is the U-value (the number
of BTUs per hour transferred through a square foot of material).
The lower the U-value, the better the performance. According to
ASHRAE HANDBOOK 1977 Fundamentals, the U-value of historic rolled
steel sash with single glazing is 1.3. Adding storm windows to
the existing units or reglazing with 5/8" insulating glass
produces a U-value of .69. These methods of weatherizing historic
steel windows compare favorably with rolled steel replacement
alternatives: with factory installed 1" insulating glass
(.67 U-value); with added thermal break construction and factory
finish coatings (.62 U-value).
"The Repair and Thermal Upgrading of Historic Steel Windows" an Historic Preservation Brief
