Historic Preservation - Technical Procedures
Preservation Tech Notes: Windows 5 Interior Metal Storm Windows
Preservation Tech Notes, National Park Service, Pad
Doors And Windows
Preservation Tech Notes: Windows 5 Interior Metal Storm Windows
PRESERVATION TECH NOTES: WINDOWS Number 5
INTERIOR METAL STORM WINDOWS
Laura A. Muckenfuss
Center for Architectural Conservation
Georgia Institute of Technology
Charles E. Fisher
Preservation Assistance Division
National Park Service
This standard includes the bulk of information contained in the
original Preservation Tech Notes developed by the National Park
Service and the Center for Architectural Conservation at Georgia
Tech. The Preservation Tech Notes are case studies of exemplary
projects designed to provide specific examples of sound
preservation techniques. To obtain a complete copy of The Window
publications, including figures and illustrations, please contact:
Historic Preservation Education Foundation
P.O. Box 77160
Washington, DC 20013-7160
The Window Handbook, jointly prepared by the National Park Service,
Preservation Assistance Division and the Center for Architectural
Conservation at Georgia Tech, also contains all of the Tech Notes
on Windows and is available for purchase from the Historic
Preservation Education Foundation for $32.00. The Window Workbook
is available for $49.00. The two publications together can be
purchased for $72.00.
OLD WATKINS NATIONAL BANK
The Old Watkins National Bank (now known as the Watkins Community
Museum) is an impressive example of Richardsonian Romanesque
architecture in Kansas. Built in 1887, the building is
individually listed on the National Register of Historic Places and
is owned by the Douglas County Historical Society.
The windows are a prominent feature of the building. The 102
windows, a majority of which are 5' wide by 10' high, are in twelve
sizes and five styles. Many have arched tops. The monumental
double-hung windows help to convey the grand qualities of the
original design both on the exterior and in the spacious interior.
Made of curly and burly pine, the windows are exquisitely trimmed
on the interior, and the distinctive natural wood grain is
especially pronounced in the jamb panels and interior shutters.
Unlike the more usual shutters which fold against the jamb, these
shutters slide vertically within multiple jamb tracks.
As with most building owners, the historical society was concerned
about energy usage and thermal comfort as well as the need to have
closely regulated environmental control to protect museum
collections. As part of an overall rehabilitation program, an
energy audit was initially performed by the local utility company.
Although the historic wood windows were well-constructed and not
seriously deteriorated, they were identified as a major contributor
to energy usage because of their number and large sizes. Single
glazing, lack of weather stripping and cracks around the window
frames all added to winter heat loss, summer heat gain and
appreciable air infiltration. As a result of the energy audit, the
project architect, James Williams AIA, investigated several storm
Use of exterior storm windows was initially explored both for
energy conservation purposes and as a way to extend the useful life
of the original windows. Unfortunately, the prices quoted for
exterior storm windows by local contractors were around $65,000,
nearly double the budgeted amount. In addition to the high cost of
exterior storm windows, one further problem with an exterior storm
application arose when it was discovered that the decorative terra-
cotta capitals adjacent to the upper level window openings returned
against the original frames. As a result, the proposed exterior
storm windows could not be easily installed in these locations
without cutting back or covering portions of the terra cotta.
The numerous problems with exterior storm windows encountered in
this project led to consideration of an interior storm system.
Here too, there were specific requirements:
1. The impressive interior woodwork around the windows could not
2. The new window unit could not alter the appearance of the
windows as viewed from the outside and the basic character of
the window needed to be preserved on the inside as well.
3. The storm window needed to have venting capability in case
condensation occurred between the storm unit and the original
sash to protect against damage to the original sill.
4. The windows needed to be less expensive than the exterior
5. The interior shutter system still used in various rooms for
sun control needed to remain operable.
6. The energy conservation objectives would have to be met.
In searching for an interior storm window that met both the
functional requirements and the concerns about visual qualities,
the architect chose a commercially available metal storm window
system. The storm window was designed to fit within the existing
wooden jamb, thus resulting in minimal damage to historic material.
The interior windows were nearly $20,000 cheaper to install than
the bids received for exterior storm windows. Of particular
significance, the storm sash were not readily visible from the
outside, and on the inside the thin bronze-finished frames blended
in well with the decorative finish and fine detailing of the
Selecting an interior storm window per se had certain inherent
advantages in this case over exterior applications: (1) no
obtrusive structural muntins were necessary because wind pressure
was not a major factor; (2) fabrication of the storm windows on the
first floor was significantly less expensive since the original
windows were squared-off at the head on the interior unlike the
arch shape found on the exterior; and (3) installation costs would
be appreciably lower since problems created by cutting back the
decorative terra cotta capitals on the exterior of the second floor
openings were avoided.
***STORM WINDOW DETAIL***
The thin aluminum storm window frame (7/8" wide, 1-1/2" deep) was
attached to a small new subframe by two pins that allowed the
windows to pivot open for cleaning and venting in case entrapped
condensation was ever a problem.
The subframe consisted of a 1/8" thick metal angle screwed to the
wood jamb, serving as a support and as a stop for the storm sash.
On the large windows, the metal angle was paired to form a
horizontal muntin, in line with the historic meeting rail, to
accommodate an upper and lower storm panel, both of which pivoted.
The frames were mounted in a location that provided a sufficiently
wide dead air space for energy conservation purposes, yet still
allowed the interior shutters to remain operable.
Mounted on pivot pins, the storm window relied on the pile weather
stripping which ran continuously along the edge of the frame to
serve as the seal between the metal subframe and the metal storm.
Neoprene weather stripping was also added to the surface of the
subframe to serve as a compression seal with the storm frame.
Clear silicone caulk between the wood jamb and the subframe
completed the seal.
***ASSEMBLY AND INSTALLATION***
The frames were custom-fitted to each opening and prefabricated by
a local glass dealer. For each of installation, the glazing was
not done at this time. At the site, the sash frames were
positioned in the existing jambs with the aid of a rolling
scaffold. A space of nearly 1-3/4" was provided between the
existing glass, which is in a very thick wood frame, and the back
of the storm glass; this space serves as a dead air pocket for
To mount the frames, holes were drilled and hardware attached for
the lock and pivot mechanisms; the storm frames were then attached
and the loose end of the hold-open arms were screwed to the metal
subframe. Once the glass was installed, the work was essentially
The storm window system chosen for the building fulfilled the
criteria established at the beginning of the project. Interior
storm windows were installed on 92 of the windows in 1981 at a cost
of $45,068 ($12.07 per square foot of opening), and an initial cost
savings of nearly $20,000 was realized over exterior storm
applications. A portion of the cost saving was attributed to the
fact that, as interior storm windows, they were installed by the
contractor during his slow winter months. The payback period for
the storm windows will be accurately determined only by in-place
performance. However, it would appear that the storm windows are
reducing the energy consumption by more than 40% - a figure that
exceeded the theoretical calculations. Long-term maintenance of
the storm windows is expected to be low because of the quality of
construction and because the windows will not be opened on a daily
Other benefits have resulted from this project cannot be directly
measured in dollars. Former hot and cold spots in the building
have been greatly reduced. Patron comfort has been noticeably
improved both thermally and from reduced street noise level.
In summary, the interior storm window solution not only provided
the owner with initial cost savings in installation, but it also
reduced fuel consumption, met all functional requirements, and
carefully addressed historic preservation concerns. The thin frame
storm window, set within the existing jamb and mounted so as to
pivot, was a sensitive solution which is also being used on other
projects involving rehabilitations of historically important
- Elizabeth M. Watkins Community Museum
(formerly the Old Watkins National Bank
1047 Massachusetts Street
PROJECT DATE: Winter 1981
- James Williams, AIA
123 West Eight
- Kennedy Glass, Inc. Contractor
P. O. Box 681
- Steve Jansen
Director, Watkins Community Museum
- Interior Storm Windows - Kawneer Company, Inc.
1105 North Front Street
- Total costs, including installation for the 92 storm windows
was $45,068, equaling $12.07 per square foot. Small storm
windows were up to four times as expensive per square foot as
the largest ones. Units were not installed on 6 attic and 4
END OF SECTION