Transom Windows: Types, Repairs, Decorative Options, and Energy Performance

A transom window is a window set above a door or another window, typically in a fixed (non-opening) configuration. The term comes from the horizontal beam (the transom bar) that separates the door or window below from the glass above. Transom windows are one of the most common architectural features in DMV residential architecture, appearing in virtually every building style from the Federal-period rowhouses of Georgetown and Capitol Hill to the colonial revival houses of Bethesda and McLean to contemporary infill construction throughout Northern Virginia.

In pre-air-conditioning residential architecture, transom windows above interior doors served a critical ventilation function — they could be opened to allow air circulation between rooms while maintaining privacy. Operable transoms above interior doors are still found in older DMV homes and apartment buildings, though most are now fixed in place or inoperable. Transoms above exterior doors and windows are almost always fixed and serve primarily to admit daylight and add architectural character to the facade.

The glass in transom windows across the DMV runs the full range of glass types: clear single-pane in older homes, double-pane insulated in more recent construction, decorative stained or leaded glass in craftsman and colonial revival properties, frosted or patterned glass in bathroom or privacy applications, and occasionally textured or art glass in architecturally significant properties. Understanding the glass in your specific transom windows is the starting point for any repair or replacement decision.

Transom windows above exterior doors are among the most common glass service calls we receive for older DMV homes. The transom is often single-pane, the glazing compound around the glass has long since dried and cracked, and the result is a drafty, inefficient entry that can be significantly improved by a glass replacement and re-glazing. This is a relatively low-cost repair with meaningful comfort and energy improvement outcomes.

The most common transom window repair calls we receive in the DMV fall into a few predictable categories. Cracked or broken glass — often from an impact during door operation, furniture moving, or from failed glazing compound that allowed the glass to shift and stress — is the most frequent. Failed seals in double-pane transom units causing fogging are the second most common. Drafty transoms above exterior doors due to dried and cracked glazing compound are the third.

Replacing a cracked or broken transom pane is typically straightforward when the transom is a simple rectangular or half-round fixed sash. We measure the glass opening, fabricate a replacement to size, and install with appropriate glazing. For decorative transom glass — leaded, stained, etched, or patterned — replacement requires matching the original glass type, which may involve sourcing specialty glass.

For transom windows with failed double-pane seals, the repair is IGU replacement. Transom IGUs are often unusual sizes that require custom fabrication. We measure the existing unit, determine the spacer bar width and glass type from the existing unit, and order a custom replacement. Custom IGU fabrication for transom replacements typically takes two to five business days.

Drafty transoms are repaired by removing the glass, cleaning all old glazing compound from the sash, reinstalling the glass with fresh glazing, and properly sealing the glass-to-sash joint. On wood sash transoms in older DMV homes, it is also common to find that the putty glazing has been painted over many times without maintenance, resulting in a deteriorated glazing bed that no longer seals properly. A proper re-glazing involves stripping back to bare wood, priming, setting the glass in glazing compound, and painting. This is restoration work that extends the life of the original sash significantly. Call (703) 470-7867 for transom repair service throughout the DMV.

The transom above the front door is the most visible glass in many DMV homes, and in historic neighborhoods it is often the most decorative. Georgetown Federal rowhouses frequently have fanlight transoms — semicircular or elliptical windows with leaded glass in a sunburst or geometric pattern. Capitol Hill Victorian homes often have rectangular transoms with colored glass borders or simple geometric leaded patterns. Craftsman bungalows in Silver Spring and Takoma Park typically have transoms with art glass inserts in muted greens, browns, and amber tones.

Restoring or repairing decorative transom glass in these historic properties requires care and knowledge of the original glass types. When a decorative transom pane breaks, replacement involves matching not just the glass size but the glass type, color, and texture. Antique art glass colors are often no longer in production, requiring sourcing from specialty dealers who stock historic glass. We maintain relationships with specialty glass suppliers for exactly this kind of sourcing challenge.

For historic transoms where the entire leaded glass panel has deteriorated — oxidized lead came, multiple broken pieces, bent or bowed panel — a full panel restoration is possible. This involves carefully disassembling the panel, replacing broken glass pieces, re-leading with fresh came, soldering the joints, and reinstalling. For historically significant properties, this restoration approach preserves the original glass and the historic character of the transom. We work with leaded glass artisans for complex panel restorations.

When full restoration is not feasible or when only the glass behind a decorative surround needs replacement, we can supply period-appropriate glass in the closest available match to the original. Restoration glass — glass made with intentional slight imperfections to replicate the character of historic handmade glass — is available for applications where the natural variation of the original glass is part of the character. Visit /guides/decorative-glass-guide for more on matching historic decorative glass types.

Transom windows are often overlooked in energy efficiency discussions because they are typically smaller than the windows and doors they accompany. But for a DC or Maryland rowhouse with a front door transom, a rear door transom, and multiple interior transoms above hallway doors, the cumulative glass area and the cumulative air leakage through deteriorated glazing compound can be significant.

Single-pane transom glass above exterior doors is a real energy weakness. The glass itself has essentially no insulation value, and old or deteriorated glazing compound around the glass creates additional air leakage. Upgrading a single-pane exterior transom to an insulated double-pane unit can be done when the sash profile has adequate depth — many historic wood sash transoms do not have the depth for a double-pane unit without modification. Where depth is insufficient, adding an interior storm glass behind the existing single pane is an alternative that improves insulation without replacing the historic sash.

For modern construction with double-pane transoms, failed IGU seals are the primary energy concern. A failed transom IGU allows moisture in and reduces the insulation value of the unit back toward single-pane performance. Prompt IGU replacement restores the insulation performance. For south or west-facing exterior transoms, upgrading to a low-E coating during IGU replacement reduces solar heat gain in summer while maintaining winter solar benefit.

Air sealing around transom frames is often as important as the glass specification for energy performance. Exterior transom windows can develop gaps between the frame and the wall as the structure settles over time. These gaps admit drafts and moisture that are independent of the glass unit condition. We inspect the complete transom assembly — glass, glazing, frame, and surrounding caulk — during any service visit and identify all the contributors to energy loss. For a comprehensive transom window energy and repair assessment, call (703) 470-7867.

Transoms are not only exterior architectural features — they appear above interior doors in many DMV homes, particularly in older construction and in more formal floor plans. Interior transoms above bathroom doors, bedroom doors, and hallway doors serve a light-transfer function that makes interior spaces feel less closed off. The glass specification for interior transoms is determined by the privacy requirements of the space.

For interior bathroom transoms, frosted or patterned glass provides privacy while maintaining light transfer. The glass does not need to be safety glazing in this application (it is above head height and not in a door panel) unless it is within reach of an occupied surface. Standard clear or pattern glass in the appropriate thickness for the sash opening is adequate. We carry a full range of interior transom glass options in clear, frosted, satin, and patterned finishes.

For interior transoms above doors in shared spaces — between a kitchen and dining room, for example — clear glass maintains visual connection between spaces while the transom provides a physical and acoustic separation. This is a classic function of the transom in traditional residential floor plans, and it is still a desirable feature in open-plan renovations where some degree of separation between cooking and dining areas is wanted.

Custom interior transoms are a renovation feature in higher-end DMV home projects. A custom etched glass transom above the master bedroom door, a stained glass transom above a home library entrance, or a reed glass transom in a contemporary open-plan renovation — these are all projects we handle, from design concept through fabrication and installation. Visit /services/custom-glass for our full custom glass capabilities, or visit /photo-estimate to start a custom transom project inquiry.