Preservation Tech Notes: Windows 15 Interior Storms For Steel Casement Windows

Procedure code:
Preservation Tech Notes, National Park Service, Pad
Doors And Windows
Storm Windows
Last Modified:



Charles E. Fisher
Preservation Assistance Division
National Park Service


Christina Henry
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.

Philadelphia, Pennsylvania


The 30-story Drake Hotel in downtown Philadelphia was the city's
largest building when constructed in the late 1920s.  The brick-
clad art deco building, accented with sculptured terra-cotta
decoration, incorporates Spanish Baroque detailing along with a
strong silhouette to create a distinctive appearance against the
city skyline.  Built with 753 rooms for use as apartments and hotel
lodging, this long narrow building has recently been renovated
exclusively for use as apartments.

The Drake Tower, as it is know today, has over 1600 steel casement
windows, richly adorned with terra cotta detail on the lower and
uppermost floors.  In between, the wall is simply detailed,
characterized by the expanse of masonry and the organization and
appearance of the steel casement windows with their multi-pane
configuration and vertical meeting line.  During the recent
renovation, the steel casement windows were maintained and their
energy performance enhanced inexpensively through the addition of
interior storm windows.


There are a number of window sizes and styles in the building
ranging from those with arched transoms on the upper floors to
small single casements stacked vertically in bathroom locations.
The predominant window type consists of a paired casement unit,
measuring approximately 3 feet wide by 4 3/4 feet high.  These
units are hinged on the jamb side, closing against a center mullion
bar.  On the interior the windows have a slightly splayed plaster
jamb, devoid of any trim except for a rather simple wooden apron.

Having established that the casement units were in relatively good
condition, the project architect examined ways to improve their
energy efficiency.  Caulking around the frames and adding
weatherstripping to the operable casement would considerably reduce
air infiltration, but would not address the heat loss through the
glass and the non-thermally broken metal frame.  Double glazing was
considered desirable and yet there were very limited choices.  The
shallow 7/8" glazing depth and narrow width of the glazing bars in
the existing frame precluded retrofitting insulating glass within
the individual lights.  Since operable windows for seasonal use
were a requirement for marketing, the addition of a fixed acrylic
or glass panel was not considered.  Similarly, an exterior storm
unit would prohibit operation of the windows, unless "piggybacked"
individually onto each of the casement pairs.  An exterior applied
storm panel piggybacked onto each operable sash would create
aesthetic problems with the appearance of the windows.


A system to improve the energy performance of the windows was
developed by the architect, based on an approach that the firm had
specified for other similar projects.  It involved the installation
of a new horizontally sliding storm window unit, mounted on the
interior of the window jamb.  The 2 storm panels would run the full
height of the opening and would slightly overlap to allow for an
effective weather seal.  The intersection of the 2 storm panels
thus would align at the vertical mullion of the existing paired
casement windows.  Since the interior face of the steel mullion was
2 1/4" wide, the visual impact on the windows of the intersection
of the frames of the two storm panels would be minimal.  For insect
control, especially on the lower floors, a screen panel half the
width of the opening was specified, set within a third track of the
aluminum subframe.


The steel casement windows required basic maintenance work.  This
work included cleaning, reputtying where necessary, limited
replacement of cracked glass, and the application of an anti-
corrosive paint.  The hardware was cleaned and oiled, and the
frames caulked on the exterior both to keep water from entering and
rusting the steel subframe as well as to reduce air infiltration.
The relatively tight closure of the cleaned and repainted
casements, coupled with the planned installation of the interior
storm unit, rendered the additional expense of retrofitting
weatherstripping to the casements unnecessary.


Several important factors were taken into account to ensure the
successful installation and operation of the storm windows.  First,
care was taken to make sure that the aluminum window section was
thick enough to prevent racking of the sliding sash.  For the 3' x
4 3/4' opening, a 5/8" thick sash frame was used, set into an
aluminum 1 3/8" subframe screwed to the existing jamb.  Openings
larger than these may require thicker frames.  Second, correct
installation procedures were essential to ensure that the slider
unit functioned properly.  This required that each subframe be
squared off when installed in the existing jamb, since changes in
alignment may have occurred to the window opening over the years.

Working one floor at a time, the aluminum storm frames were custom
fitted to each opening and prefabricated by the window company.
Installation work was easily scheduled since all work could be
accomplished from the inside.  After the frames were installed, a
silicone sealant tinted brown was applied around the intersection
of the aluminum subframe and the existing jamb on the exterior face
to reduce further air infiltration.  In addition, the sash stiles
had pile weatherstripping on the inner and outer faces for
additional tightness.


The cost of repairing and repainting the historic steel windows was
$55,000, or $34 per window.  Installation of the combination
storm/screen interior unit averaged $62 per window for the
approximately 1600 windows, bringing the total cost to $96 per


The installation of the storm units had little visual impact on the
exterior appearance of the Drake.  This is largely due to the
selection of an interior application, use of a dark color for the
storm frames, the alignment of the intersection of the two storm
panels at a point behind the steel mullion on the historic window,
and the setback of the storm unit nearly flush with the interior
wall.  On the inside, the storms are neatly set within the opening
and aesthetically are not disruptive.

Potential condensation problems exist with many storm window
applications.  The window contractor initially had expressed
concern over possible condensation forming on the windows directly
above wall air-conditioning units.  This certainly was a problem
with the historic windows.  With installation of the storm units,
there has been no problem with condensation forming on the windows
over the past two years.

Much of the success of sliding aluminum sash rests on the use of
good frames and hardware, and on proper installation.  While
friction sliders were used for the sash, more expensive ball-
bearing rollers would have provided for smoother operation.  The
subframes for the storm and screen panels are properly squared in
each opening and preclude the storm units from catching or jamming
during operation.  The storm windows along with the historic
casement unit have provided a sound weather seal.  An added benefit
of the work was that the street noise has been considerably reduced
within the apartments, particularly on the lower floors.

This simple method for upgrading the performance of the windows
proved both practical and cost effective, while preserving both the
appearance and the materials of the historic windows.



-    The Drake Tower (formerly Drake Hotel)
    1512-1514 Spruce Street
    Philadelphia, Pennsylvania


-    Samuel Mindel and Eric Rosenfeld
    New York, New York

PROJECT DATE:  March 1984 - May 1986


-    Repair and repainting of approximately 1600 windows cost
    $55,000.  The cost of the interior storms averaged $62 per
    window, totaling approximately $100,000.  The total cost of
    the window work was $155,000, or $96 per window.


-    Richard Klein
    Goldfarb/Klein and Associates
    260 South 23rd Street
    Philadelphia, Pennsylvania

                             END OF SECTION
Last Reviewed 2012-02-24