According to Religious Product News, a majority of the approximately 400,000 religious buildings in America contain some form of inspirational stained glass. About 1 percent of churches have windows valued at $1 million or more. A professional appraisal may be required to fully establish the value, but you can follow the same steps an appraiser would to get some idea of their worth.
Create a Photographic Record
Clear photographs can give you a guide on how to restore or replace windows and help out in the research phase. You may need to compare photos to those in reference books or send them to a glass expert to help identify the value. Take wide-angle photographs to show the placement of each window within the church. The shots should document each window's subject, condition, composition and the signature of the artist if there is one. Store a copy in a safe place, and send another to the church's insurance company.
Research the History
Find out as much as possible about the history of the windows, including the date of installation, the artist and the originating studio. If church records don't have that, consult a stained glass reference books or expert. Generally speaking, older windows are more valuable than contemporary creations. Windows created by well-known artists cost more than those of unknown authorship. The replacement value for windows created before 1955 by artists Connick, Lamb, Payne or Willet may be $900 or more per square foot. Windows created by John LaFarge, Louis Comfort Tiffany or their contemporaries in the late 19th to early 20th centuries may be priceless, especially if they are signed by the artist.
Checking Style and Condition
Measure each window and write down details about its style and condition. In general, smaller windows are more valuable than larger ones, since they require more glass cutting and lead. Note in detail the glass composition and design. For example, windows made with single pieces of colored glass are generally less valuable than those with multiple pieces sandwiched together to create different shades. Designs containing curved glass cost more than those with straight edges. Also note any damage to the glass, leading or framing. You need details such as these to determine what it would cost to replace them.
There are usually at least two ways to establish the value of such windows -- the fair market value and the replacement value. To estimate fair market value, consult auction records or art guides to see prices of windows of similar age, style and composition. For insurance replacement value, get estimates of the cost to replace each window using contemporary materials and artistry.