Windows

Windows are a significant feature of buildings and should be retained and preserved with their original functional and decorative features. The window material and how the window operates (e.g., double hung, casement, awning, or hopper) are significant, as are its components (including sash, muntins, glazing, pane configuration, sills, mullions, casings, or brick molds) and related features, such as shutters.

 

Protection and Energy Efficiency

  • The wood or metal which comprises the window jamb, sash, and trim should be protected through appropriate treatments, such as cleaning, paint removal, and reapplication of protective coating systems.
  • Windows should maintain a weathertight seal by recaulking gaps in fixed joints and replacing or installing weatherstripping.
  • Storm windows may be added that match or have a one-over-one pane configuration that does not obscure the historic window characteristics. Alternatively, interior storm windows may be appropriate.
  • Historic operability of windows should be retained by lubricating friction points and replacing broken components of the operating system (such as hinges, latches, sash chains or cords) and replacing deteriorated gaskets or insulating units.
  • Historic windows may be retrofitted with high-performance glazing, clear film, or low-emissivity (low-e) glass to reduce solar heat gain, if the historic character can be maintained.
    • Film installed in a slightly lighter shade of the same color tint when replacing glazing panels on historically dark tinted windows to improve daylighting is allowed.
  • Single-glazed sashes may be modified to accommodate insulated glass or low-e glass when it does not jeopardize the soundness of the sash or significantly alter its appearance and spacer grids match the color of the window sash.
  • Installation of light-control devices on the historic building where appropriate to the building type, such as light shelves in industrial or mid-century modern buildings, awnings on some commercial and residential buildings and shutters on residential buildings that had them historically is permitted.

 

Elements of a window

Window Diagram.jpg

 

Repair

  • Preserving historic window material should be prioritized.
  • Window frames and sash may be repaired by patching, splicing, consolidating, or otherwise reinforcing them using recognized preservation methods should be the first option.
  • Repair may include the limited replacement in kind or with a compatible substitute material of those extensively deteriorated, broken, or missing components of features when there are surviving prototypes, such as sash, sills, hardware, or shutters.
  • Special care should be given to repairing and maintaining leaded-glass or stained-glass windows. If beyond repair, the replacement should be with a similar window.

Replacement

  • Replacing in kind an entire window should be considered only when the window is too deteriorated to repair.
  • Replacements should match the material, type, size, operation, and divided-light configuration and pattern. While wood is the most common historic window material, buildings constructed mid-century often have steel and aluminum windows that would have been original to the structure and therefore historic.

  • True divided light windows are preferred, however simulated dived lights with a spacer bar (interstitial spacer between the double-glazed panes of glass) are allowed. Muntins between panes of glass are not allowed except on floors above the third level of taller buildings.

Divided Lite-Authentic.JPG

True Divided Light: Each muntin holds a separate piece of glass, so for a four-pane window there are four pieces of glass held by each set of muntins

Divided Lite-Simulated with Spacer.JPG

Simulated Divided Light with Spacer: two panes of glass are separated by a spacer bar with muntins applied on the outside of the glass.

Divided Lite-Grill between glass.JPG

Not Recommended: Muntins are placed between the two panes of glass on the inside.

 
  • Replacement windows should be durable, repairable, and recyclable and may have two or three panes for increased efficiency.

  • If using the same kind of material is not feasible, then a compatible substitute material such as aluminum clad wood windows or fiberglass windows with a similar profile and color as the original window may be considered. Given the poor environmental impacts, low quality and durability, and negative visual impact, vinyl windows should not be used regardless of visibility.

Aluminum Clad Wood Window 2.jpg

Aluminum clad wood window without screen (left) and with screen (right)
  • To accommodate a new use, deteriorated windows may be replaced with new windows that operate differently. Any change must have minimal visual impact. Examples could include replacing hopper or awning windows with casement windows or adding a realigned and enlarged operable portion of industrial steel windows to meet life-safety codes.
  • Non-historic windows may be replaced with new windows that are compatible with the historic character of the building.
  • Windows that have been formerly blocked or closed in should be reopened with a window that replicates the original to the extent possible based on photographic evidence and is energy efficient.

New Openings

  • New window openings are appropriate for rear or secondary facades if required by a new use such as residential in a former warehouse building.
  • New openings and the windows in them should be compatible with the overall design of the building but, in most cases, not duplicate the historic fenestration. New openings on the primary façade are discouraged.

Egress

  • Locate new or expanded egress windows on secondary, non-street facing facades if possible.
  • If egress is required on a primary or front façade, maintain the width and header height of the existing opening, when possible.
  • If the new egress replaces the original window, the new window should match the original material.
  • Visible window wells should not protrude more than 6 inches in height above grade.
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