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.

Old House Journal - - Quick Makeovers - By Alex San­tan­to­nio

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.

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