Repair, Don't Replace: Restoring Historic Windows

One of the most common jobs for anyone that preserves or restores historic buildings is window restoration. Old windows can be finicky, drafty, and lack the insulative properties of modern sash, a reason that many homeowners and contractors opt to replace them. Often these fastidiously handmade relics are just tossed into a dumpster. A properly restored wooden sash, however, can last for centuries, reducing the amount of waste that ends up in a landfill, and cutting down on the need for new materials.

Usually, it’s the lower sash that needs the most work as this frame is subject to more wear from opening and closing. Window frames are made of stiles, the vertical pieces in the frame, rails, the horizontal pieces in the frame, and muntin bars, the thin pieces that divide the glass. The lower rail is generally where most problems are found because water that accumulates on the sill can result in rot.

There are a few different options when it comes to repairing the lower rail of a window sash. The fastest is to remove any rotten wood with the frame still intact and fill the sections with a heavy-duty epoxy like West System or Abatron. As a woodworker, though, I prefer the more time-consuming method, cutting patches, known as dutchman, from wood and fitting them like puzzle pieces into the places the original wood has disintegrated. The dutchman can be glued and nailed for strength. If the joinery at corners has rotted, it may be necessary to take the frame apart, and repair the mortise and tenon that interlock each piece. Once your frame is restored, you’re ready to reglaze and reinstall. This should ensure your windows are good for the next few decades!

About the Author: Lee McColgan has worked as a traditional builder and preservationist for the last decade. His projects have been featured in the Boston Globe and Architectural Digest and he’s appeared on HGTV’s Houses with History. He will teach classes on historic preservation and hand tool technique at Saratoga Joinery.