The Preservation Brief onThe Repair of Historic Wooden Windows published by the National Park Service, characterizes ‘significance' in the broadest terms. It states that windows should be considered significant to a building if they: are original, reflect the original design intent for the building, reflect period or regional styles or building practices, reflect changes to the building resulting from major periods or events, or are examples of exceptional craftsmanship or design.

"As ‘character defining features,' windows are subject to a rather strict analysis," says Dr. George C. Skarmeas, AIA, Principal, Director of Historic Preservation for Hillier Architecture. He lists the areas in which all projects, small or large, simple or complex, are evaluated:

• Significance as character defining features. Determine if windows are original, and what changes have been made over time.
• Presence of significant fabric, information and historic evidence. This includes paint structure and history of paint layers, i.e. a comprehensive seriation analysis.
• Performance characteristics, both as an element of the original design, and construction and as an element of a new use plan. This area, he notes, is one of the most difficult to deal with.
• Overall condition assessment and organization in different categories of conditions and deterioration, such as good, moderate, and severe.
• Treatment options, including surface treatment to reconstruction and replacement.
• Construction costs
• Sequence of implementation. This embraces in-situ repairs to careful removal, and off-site restoration.

The information gained from such careful analysis, Skarmeas explains, will supply critical answers to a number of issues such as:

• The role windows play in the overall design of the historic resource.
• The important information they provide as part of the history of the building-its original colors, sequence of colors, and finishes.
• Clues as to how they have performed over time and where their weaknesses are.
• Deterioration patterns that may exist.
• Performance limitations against modern criteria and expectations, especially if there is a significant change in use.

A graphic or photographic system will record existing conditions and illustrate the scope of any necessary repairs. Another effective tool is a window schedule, which lists all of the parts of each window unit and notes their condition.

In any analysis the following should be noted:

• Window location
• Condition of the paint
• Condition of the frame and sill
• Condition of the sash, rails, stiles, and muntins
• Glazing problems
• Hardware
• The overall condition of the window such as excellent, fair, poor

Equally important is documentation regarding the qualities inherent in the windows, which make restoration worthwhile and, on occasion, have been known to evoke inspiration.

Many factors, such as poor design, moisture, vandalism, insect attack, and lack of maintenance can contribute to wood window deterioration, but moisture is the primary contributing factor in wooden window decay. Sills seem to fail first because they are exposed to beating sun, freezing rain, snow and bird droppings.