Architecture is inhabited sculpture.
  — Constantin Brancusi       (1876-1957)




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The L'Enfant Trust, Washington, DC

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The Windows Issue

The replacement of historic windows has become one of the hottest and most debated historic preservation issues in the past decade, even triggering many preservation organizations to place historic windows on their Most Endangered Lists. Most historic property owners will come to a point when they must decide to restore or replace their existing windows. To address the issue, The L'Enfant Trust has compiled this guide and checklists for property owners as they contemplate the best option for their property.

Figure 1

Why are historic windows so important?
Original windows are a key element in telling the story of a historic property and can often lead to determining what styles and technologies were contemporaneous with the construction of the building. For example, windows from the 18th to the mid-19th centuries usually had small divided-lites, or small panes of glass, with thin and elegant muntins. See diagram below. Only small panes of glass were available at this time, so you would typically see 6-over-6, 9-over-9, or 12-over-12 lite configurations. With the advancement of technology in the Victorian period, large plate glass was readily available and used in fashioning 1-over-1 or 2-over-2 windows. The beginning of the 20th century experienced a rebirth of Colonial style architecture and many windows had six or nine individual lites over one large pane of glass in the bottom sash.

Nearly all historic windows were made with exceptional materials and craftsmanship. Prior to the 1950s, most windows were constructed of old-growth wood, which is stronger and more rot resistant than any wood available on the market today. Retaining historic windows not only protects the historic and architectural integrity of the property, but also conserves these rare materials and the embodied energy used to create them.

Restoration vs. Replacement
Frequently, homeowners complain of air infiltration through their old windows and high energy bills. It's important to remember windows like other elements of your building need regular upkeep and attention. Before considering window replacement, you should inspect all areas of the building particularly the roof, where most energy is typically lost. The Secretary of the Interior's Standards for Rehabilitation state that historic windows are not beyond repair "solely because of peeling paint, broken glass, stuck sash, and high air infiltration."

That said, if your existing windows are not original to the property or are assessed by an expert to be beyond repair, window replacement may be appropriate. Wood replacement windows are usually the most appropriate choice for replacing an existing wood window, but as always check with The L'Enfant Trust to discuss your options. Also, keep in mind, the replacement windows approved for your neighbor's replacement project may not be the appropriate windows for your property. At the Trust, many items are taken into consideration before a window replacement proposal is approved: architectural style, date of construction, and the type and condition of the existing windows.

Be Careful
Window manufacturers' specifications for "wood windows" have to be carefully reviewed. Some makers refer to their product as wood but the actual product is wood with a vinyl or aluminum cladding on the exterior of the window. Exterior cladding has a shiny and reflective appearance and makes it more difficult to recreate the profiles of the original window. A further caution is to understand that no window is "maintenance free" contrary to some promotional claims. Modern replacement windows have their own set of problems, including the failure of insulated glass (fogging) and interior wood rot (moisture trapped behind the exterior cladding). Well maintained historic windows made of old-growth wood can be repaired and restored to last for well over a hundred years. Many windows available today are mass produced and when they fail the entire window must simply be replaced.

A common misconception is that window restoration is more expensive than replacement windows. As a general rule, restoration of an existing window will be less expensive than replacing it with a quality replacement window. Restoration also keeps discarded materials out of landfills and supports local craftsmen and businesses.

Checklist for Replacement Windows

Observe your windows: original window opening size, sashes, muntins, glass, jambs, brickmoulds, decorative trim work, and sills

Figure 2

Replacement windows must replicate the size, operability, and profile of the original windows. Divided-lite windows must be true or simulated (interior and exterior muntins with a spacer bar between the panes of glass) divided-lites. No removable muntins or muntins sandwiched between the glass
No aluminum or vinyl capping of wood brickmoulds
No tinted or reflective glass
Jambs should be painted to match window frames
Your Request for Change form should contain photos of the existing windows and specifications for the proposed windows, including material, dimensions, style, profile, trim & finish

In addition to Trust review, a city permit is also required for all window replacement

Figure 3

Figure 4

Caring for Historic Windows
Windows like any other part of a building need regular maintenance to prevent deterioration. Wood windows can be weather-stripped to eliminate air infiltration and repaired with epoxy (resin) for small repairs and/or Dutchman repair (wood patch) for larger areas of deterioration. Also, some historic windows can be retro-fitted with insulated glass.

Furthermore, if your existing windows were last painted prior to 1978, you may need to inquire about lead abatement. A skilled and experienced restoration contractor will know the proper and safest way to remove lead paint on the exterior and interior of your historic windows.

Window Maintenance and Repair Checklist
Replace weather-stripping as needed
Keep window frames and sills caulked
Replace glazing putty around glass panes as needed
Keep windows painted: a good coat of paint will prevent deterioration. Remember - too many coats of paint may cause the window to not open or close properly
Use storm windows

Figure 5

Figure 5

Storm Windows:
Conserving Energy and Preserving Historic Character
Storm windows have been used for over 100 years and are a very efficient way of protecting the original window sashes and glass. Storm windows contribute to energy efficiency in two ways: reduces air infiltration between the sash and framing and provides a second layer of glazing that reduces heat loss through the glass.

A quality storm window can also decrease the time needed for routine maintenance, such as repainting, weather-stripping, and caulking. Storm windows are also easy to install and can be fitted with screens during the spring and fall seasons. The highly regarded Lawrence Berkeley National Laboratory and the National Park Service claim that a leaky wood window with a storm window performs similarly to a newly installed replacement window.

Figure 6

Storm Windows Checklist
Fits into the existing window opening
Clear glass only
Frame color of storm window should match color of existing window sashes and framing
The meeting rails or other necessary divisions on the storm window should align with major divisions of the window
Storm window should be installed no more than two inches away from the window
Exterior storms should have weep holes to allow moisture to escape

Figure 7

Contact Information

Restoration Contractors

Phoenix Restoration Group

Blaine Window Repair Service
(Window Replacement Parts)

Monarc Construction
John Bellingham

Mozer Works, Inc.
Neil Mozer
301 920-1900

Renew Restoration
Mark Wesolowski

The Craftsmen Group, Inc.
Christian Kelleher

Traditional Builders, Inc.
John Waters

Storm Windows

Click here for a list of storm window manufacturers

Additional Resources

National Trust for Historic Preservation
resources and links on historic and replacement windows

Preservation Brief 9: The Repair of Historic Wooden Windows
guidelines on window restoration from the National Park Service

What Replacement Windows Can't Replace:
The Real Cost of Removing Historic Windows

article from The Association for Preservation Technology International

Window Repair and Replacement: Preservation and Design Guidelines preservation guidelines for Washington's historic landmarks and districts from the D.C. Historic Preservation Review Board

Lauren O. McHale
Director of Preservation

Carissa Demore
Intern, Historic Preservation Master's Degree Candidate


Donation Request
Like most non-profit organizations, The L'Enfant Trust relies on charitable cash donations from the public. Please consider making a voluntary, tax-deductible donation of $50 or more to the Trust — particularly if you find our Built to Last e-bulletin helpful in caring for your historic property. Thank you for your support.

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