Transom Window

What a Transom Is For

A transom is a window above another opening — above a door, above a storefront, above a window. It is one of the oldest pieces of building sense there is, and it does three things at once.

It brings daylight deeper into a room. Light entering high travels further across a ceiling than light entering at eye level. In a deep brownstone room, or a hallway with a single elevation, a transom is often the difference between a usable space and a dark one.

It ventilates at high level. Warm air collects at the ceiling. An opening transom lets it out, and in the days before air conditioning that was why every apartment door in New York had one above it.

It gives light without giving privacy away. A transom above a door lights a hallway without anyone being able to see through it from standing height.

Fixed or Operable

Most modern transoms are fixed, which is a missed opportunity where the room would benefit from stack ventilation.

Where a transom does open, an awning is the usual arrangement — hinged at the top, opening outward at the bottom, so it forms a canopy over its own opening and can stay open in rain. A hopper is the inward equivalent.

Reach is the practical problem: a transom is by definition out of arm's reach. A chain operator or an electric operator solves it, and on a stairwell or double-height space an electric operator is usually the only workable answer.

The Code Points

Safety glazing is required in panels adjacent to doors, and a transom directly above a door generally falls within that. Tempered or laminated, not ordinary annealed glass.

Ventilation area. Where a transom is contributing to the openable area required for a habitable room, only the part that actually opens counts — a fixed transom contributes nothing to the ventilation calculation, however much light it brings in.

Over a circulation route. Anything above a walkway or a corridor should be laminated, so that a failure does not drop glass on people below.

Historic Transoms

New York's older housing stock is full of them: fanlights over brownstone entrances, leaded and stained transoms in pre-war apartment buildings, the hinged glass panels above apartment doors that are now almost always painted shut.

These are frequently original, frequently single glazed, and frequently in a historic district where the profile and the glazing pattern are governed by the approval. A conventional insulating unit will not fit an original transom rebate. Where performance is needed inside an approved historic profile, vacuum glazing at around 8mm is usually the only route.

Where an original leaded or stained transom survives, restoring it is normally a better outcome than replacing it, and on a landmarked frontage it may be the only permitted one.

Where Transoms Come Up

These describe the kind of work each area brings rather than any specific client project.

Brownstone and rowhouse entrances — Park Slope, Carroll Gardens, Bed-Stuy, Harlem. Fanlights and entrance transoms, usually landmarked, usually original. Restoration or careful replacement to an approved profile.

Pre-war apartment interiors — upper Manhattan, the Bronx, central Brooklyn. Over-door transoms, mostly painted shut. Freeing and repairing them is a cheap improvement to a dark interior hallway.

Storefronts — Flatbush, Coney Island Avenue, Fifth Avenue Park Slope. Traditional shopfronts have a transom band above the display window, and on a landmarked frontage it is part of what the review expects to see.

Stairwells and double-height space — townhouses and loft conversions citywide. High-level ventilation with electric operation, where nothing else is reachable.

Tell us the opening size, whether the transom should open, and whether the building is in a historic district. We supply and install across Manhattan, Brooklyn, Queens, the Bronx and Staten Island, and throughout Northern New Jersey, the Jersey Shore, Philadelphia and the Lehigh Valley.