Repairing a Modern Window Sash – GreenBuildingAdvisor

By Tom Gensmer | September 3, 2025

Tom Gensmer shares his expertise in repairing contemporary window sashes. He explains how modern windows, despite their diverse construction styles and materials, can often be repaired cost-effectively rather than fully replaced. The article details his process of carefully removing sashes, investigating damage, fabricating new rails when necessary, and using epoxy and wood patches to restore deteriorated parts.

Contemporary Window Repair

Over the years that I’ve worked as a general contractor in the Minneapolis area, I’ve been asked frequently to repair or replace deteriorated window sashes. The more of these projects I’ve completed, the more I’ve learned, and the more my interest has grown. I’m inspired by the challenge and detail of window work—so much so that I’ve been traveling regularly to Colorado for classes at Alpine Technical Workshops to better learn how to build windows. This deep dive into window joinery and hardware has informed my repair and restoration work. I’ve invested in new shop equipment that allows me to build new windows efficiently and well when repair isn’t possible or wanted. And I have positioned my business to attract more of this type of work.

While there are lots of talented craftspeople who specialize in rehabilitating historic windows, very few seem willing or able to work on contemporary ones. I generally think of windows in four categories: pre-1945, mid­century, contemporary, and high performance. Pre-1945 is self-explanatory; midcentury covers the transitional designs from the 1950s through the 1970s; contemporary covers most windows produced from the 1980s to today; and high performance is a term I use loosely to describe European-style windows such as triple-pane tilt-and-turn units.

Though it’s easy to date windows, it’s not so easy to categorize their construction characteristics, because even within any of these time ranges, many…