Specification Requirements for Proposed
Window Replacement
in Historic Buildings


State Historic Preservation Office
Oklahoma Historical Society
800 Nazih Zuhdi Drive
Oklahoma City, Oklahoma  73105

Property owners and developers undertaking historic rehabilitation projects are encouraged to repair and retain existing historic windows.  In some cases, replacement windows may be justified.  In order to review replacement windows for conformance with the Secretary of the Interior's Standards for Rehabilitation the following minimum documentation should be provided:

  1. Clear photographs of existing windows.  When windows are boarded over, remove boards from typical windows in order to take photographs.  If the rehabilitation work is complete, take additional photographs of the replacement windows.

  2. Drawings illustrating the horizontal and vertical sections of existing windows.  These drawings should include the head, jamb, sill, and muntin section details. 

  3. Drawings illustrating the horizontal and vertical sections of proposed replacement windows.  These drawings should include proposed head, jamb, sill, and muntin section details.

  4. When historic windows do not exist, sections of proposed replacement windows should still be provided.  For information about appropriate window design in this case, contact the State Historic Preservation Office.

Replacement windows should accurately replicate the appearance of existing historic windows.  All too frequently, the profiles of muntins, sash, frames, and moldings in replacement windows are different than those of historic windows.  For example, the muntins in a new double-glazed window may be much wider and flatter than the existing window muntins.  Even though the new window may duplicate the number of existing window panes, the character of the historic window is lost due to the change in design and relief.  This can alter the overall character of the building.

Another problem with many replacement windows is the use of panning, a metal molding which is installed over the molding that surrounds a window, or which replaces the existing molding altogether.  When panning does not match the existing molding, the design of the historic window is further altered.  Additionally, replacement windows of materials different from the materials of the historic windows may also vary the dimensional interpretation of the windows in the historic context of the rest of the building, thus compromising the historic character of the entire building. 

Because of the potential problems in choosing an appropriate replacement window, window sections should be drawn.  Cut both horizontal and vertical sections ("a" and "b" in Figure 1).  The sections must be carefully detailed so that all parts of the window are shown and materials are specified. 

Window sections must show the profiles of muntins, meeting rails, sash, frames, and moldings.  Treatments such as replacement moldings or panning, as well as the window's relationship to the existing wall plane, must also be detailed.  Below are examples of vertical window sections of a historic wood window with single glazing (Fig. 2) and a wood replacement window with insulated glazing (Fig. 3).  Horizontal sections should be drawn similar to the vertical sections.  Because the sections are at the same scale, the two windows can be compared.  The replacement window and the detail of how the window fits into the exterior wall in this case closely resembles the existing window's design and therefore meets the Secretary of the Interior's Standards for Rehabilitation.

 

For more information contact:
State Historic Preservation Office
Oklahoma Historical Society
800 Nazih Zuhdi Drive
Oklahoma City, Oklahoma  73105
(405) 521-6249

 

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