Preservation by Prevention: Preserving the Irreplaceable

Consequences of Lapsed Maintenance

1Preventative maintenance is an essential element of property ownership. Historic properties, like all buildings, require regular monitoring and upkeep to remedy minor maintenance issues and to guard against significant, and costly, problems down the road. Delayed maintenance can quickly transform a minor issue into a major threat, requiring complete replacement of affected building elements. This poses a significant problem for historic buildings, which often feature superior materials that cannot be reproduced and craftsmanship that cannot be replicated. Modern reliance on mass production, and modernized construction and technology, eliminated many original products and have left few craftspeople with familiarity in historic construction techniques.

This newsletter is the first in a two-part series about irreplaceable elements of historic properties. This month, we’ll focus on historic windows – next month, look for information on ironwork, masonry, and decorative details.

A coat of paint is likely the only difference between two sets of formerly identical windows pictured above, which date from the same period, utilize the same materials, and have been subject to the same environmental conditions. This simple maintenance action has ensured that the windows of the property on the left will remain a handsome, distinctive feature for years to come. The windows on the right, which were left unpainted and exposed to water infiltration and subsequent damage, will likely require complete replacement – an alteration that will permanently change the appearance of the façade.

12Windows, more so than any other functional feature of a property, imbue a building with an immediate sense of history and character, visually communicating a wealth of information regarding the age, style and period of a building, and provide a glimpse into the history of the building, neighborhood and community of its original occupants.

Historic windows were built with the expectation of maintenance and repair. Designed to be repaired over the course of their functional life, an existing 100-year-old window, if properly maintained, could last another 100 years. (Modern replacement windows, on the other hand, are built with the assumption of perpetual replacement cycles, and most will require this within 10-30 years.) But when left unprotected, the structural and decorative elements of historic wooden windows are prone to decay from exposure to sunlight and water damage, and moisture infiltration.

You can replace your historic windows, but you may never be able to replicate them exactly. Historic window professionals may be able to recreate the dimensions and pattern of the original window, but the old-growth wood used to construct windows in the 19th and early 20th centuries is no longer available. Old-growth lumber was extremely durable due to high-quality stability provided by slow-growing trees with multiple growth rings per inch; the wood available to modern contractors is the softer fast-growth variety, which, in addition to its shorter life span, is markedly less durable than the old-growth variety.

House with Original Windows

House with Original Windows

All historic window frames require maintenance, regardless of material. Like their wooden counterparts, leaded and stained glass windows are at risk from water damage and moisture infiltration, which can cause their steel frames to warp, fail to close correctly, or corrode shut completely. As replacement steel windows can be difficult to locate, and prohibitively expensive, leaded glass is often reinstalled into new, replacement aluminum window units. The frames of the aluminum replacements need to be much wider to support the leaded glass, requiring the removal of a significant portion of original glass – vastly altering the appearance of the building façade. Unfortunately, in many situations the corrosion is merely superficial, and the frames could have been repaired by prepping, painting and realigning the frames.

Original window glass can also prove challenging to replace. Locating glass that is identical – or even substantially similar – to the original piece can be extremely difficult, and costly to manufacture. Historic glass was not mass-produced, and can vary tremendously from batch to batch. Variations in colors and textures are almost endless. As with wood windows, environmental factors have contributed to the difficulty: In the 19th and early 20th centuries, glass was often colored with ingredients like lead and cobalt – elements that have since been banned for environmental or health reasons.

House Next Door with Vinyl Replacement Windows

House Next Door with Vinyl Replacement Windows

Other features are wholly unique through an accident in manufacturing, like the ‘purpled’ glass panes found in Boston’s Beacon Hill and Back Bay neighborhoods. Between 1814 and 1824, glass was shipped from England with high concentrations of manganese oxide that turned the glass purple over time and sun exposure. The original purple-tinted panes remain in only a handful of houses, and once lost, cannot be replaced.

Decreases in production had a similarly chilling effect on historic replacement features such as pigmented structural glass, which enjoyed widespread popularity through the early 20th century in the United States. It fell out of favor as manufacturing costs increased and national tastes changed, and production appears to have ceased entirely within the last decade. Few inventories have been discovered and the only active suppliers in the world are located near Bavaria, in western Germany. Even these factories produce the pigmented glass in small batches, which creates color variations.

If you own a property with its original windows still intact, there are simple steps you can take to preserve the historic window material:

  1. Get acquainted with your building. Educate yourself about its unique features and idiosyncrasies. Contact your local preservation commission, historical society, or public library. These resources may be able to provide you with information on the architect, architectural style, building materials, and other unique characteristics of your buildings. Familiarize yourself with and document interesting or notable features like stained or leaded glass, unusual window mullions, decorative stone or iron work, building materials or masonry treatments. Learning about your historic property is a valuable way to increase your appreciation of the history of the property, and connects you to the history of your building, neighborhood, and community.
  2. Inspect your windows: take a close look at your building once or twice a year (the springtime is recommended). Make note of any elements that look like they may be deteriorating, or susceptible to damage in the near future so you can monitor any changes and address problems as they arise. Check for peeling paint, splintered wood, insect infestation, rust, mold or mildew accumulation, and chipped or spalling masonry.
  3. Maintain! Minor maintenance can make a world of difference. Clean accumulated areas of dust, soot, insect cocoons, or cobwebs. Cut back any overgrown vines, which can damage the masonry. Make sure drainage is adequate, and cut back any overgrown shade trees or shrubbery to ensure that sunlight is striking the building. Eliminating opportunities for moisture accumulation and water damage will significantly reduce later maintenance costs. If necessary, have areas of peeling paint removed and repainted to guard against water damage.
The central row of windows features the original steel casement windows, windows at the upper and lower floors have been replaced with modern replacements.

The central row of windows features the original steel casement windows, windows at the upper and lower floors have been replaced with modern replacements.

If damage has progressed to the point where total replacement is the only treatment option, thoroughly document the ‘before’ conditions of the windows, so their original conditions will at least be preserved in photographs. Then, see what opportunities may exist for in-kind replacement. This is another area where local preservation groups and historical societies can be an extremely valuable resource.

Architectural salvages provide a viable option, especially in replacement stone, steel frames, and glass, and may be able to provide materials that most closely resemble the original element.

Historic window and masonry professionals are another excellent resource for locating historic building materials and, if original materials are not available, the best resource for recreating the damaged feature. Local historic commissions, preservation commissions may have an inventory of these professionals in your area.

Windows are one of the most important elements of an historic property. Maintaining the condition of your windows is an essential element in preserving the social, cultural, and architectural history of a building, as well as the community in which it exists, and is vital in sustaining the link between the past and the present that historic preservation endeavors to maintain.

In the next Preservation by Prevention: Preserving the Irreplaceable, we will explore the maintenance of historic ironwork, masonry, paving materials, and decorative elements.