How Transom Windows Work
An OHJ reader gives a step-by-step account of replacing a transom operator for functioning over-door windows that open and close.
Transom windows over most of the doors in our 1880s row house are important to its authenticity. Transoms historically were used to allow passage of air and light between rooms even when doors were shut. They make perfect sense in row houses, which typically have long, narrow floor plans with windows only at the front and back.
This house originally had four transom windows; all were painted shut. My wife, Wendy, and I not only restored them, but also added two more, including one completely fabricated in our basement woodshop using salvaged glass.
The mechanisms for working transoms were diverse in their construction and styles. They include bottom-hinged transoms with latches and chains that had a long pole to pull the latch open; sidehinged transoms that opened like doors; and top-hinged transoms with fixed lifts that could be hand-operated.
The most common type uses a long rod to operate a lift mount bracket attached to the transom sash. Restoring an existing transom is fairly straightforward, provided the window is in good condition and you have all the operable parts.
To make a transom window operational, the goal is to install it so that the window can be opened to a 30-degree angle or so. That’s enough to allow airflow without making the window hard to open or close.
The window lift operator should be set at a comfortable mounting height for an average adult to easily slide the window open. We mounted the clasp of our transom at a height of 50" above the floor, roughly the same as a light switch. If you want to set the lift operator higher, first pinch the clasp and move the rod completely into the “up” position to fully extend the rod. This is important to ensure
the rod won’t run into the ceiling when it’s all the way up.
Once you’ve got the location of the clasp on the trim, hold the assembly in place and mark the screw locations. While continuing to hold all in place, have another person climb onto a stepstool or ladder and place the upper support bracket about 1" above the lift’s hinge. Then mark those screw locations. Remove and drill your pilot holes based on the marks. Then simply drive screws to secure the mount.
Placing the rest of the components is pretty simple. Secure the clasp and supports in your pilot holes. (The middle support piece is still not attached at this point.) Next, pinch the clasp and lower the rod so that the hinge assembly, when collapsed against the wall, puts the top of the mount bracket near the upper support piece, and the upper section of the rod is still within that same support. This will give you the position of the rod when the transom is fully closed.
Climb back up the ladder and position the lift mounting bracket against the sash to determine and mark screw hole locations for the mounting bracket. To drill the screw holes for the bracket, put some tape on your drill bit to mark the drilling depth based on the screw length.
Finally, position the middle support bracket where it will not impede the function of the lift, drill pilot holes, attach the support bracket with screws—and step back to admire your functional transom. If the mechanism is balky, add a squirt or two of WD40 to keep it squeak free.
Bringing light and air to the vestibule, this restored transom window and operator are at the row house entry.