What Is a Transom Window? Types, Benefits, Sizes, Costs, and Installation Guide

Key Takeaways

A transom window is a slim glazed panel installed above a door or larger window to add daylight and, if operable, ventilation—making rooms feel brighter and taller without major remodeling.
Options include fixed for maximum light and clean sightlines, or operable (awning/hopper) for stack ventilation and airflow; choose based on room function and climate.
Styles and materials span rectangular or arched fanlights in wood, fiberglass, aluminum, or vinyl, with clear, frosted, textured, or laminated glass for privacy, sound control, and security.
Size smart: common heights are 10–18 in and widths match the door/window below; align mullions and head heights for balanced proportions and consistent sightlines.
Meet code and performance: use safety glazing near doors (IRC R308), target ENERGY STAR U-factor/SHGC for your climate, and flash/air-seal per ASTM E2112 to prevent leaks.
Budget guide: typical units range from about $270–$700 installed for entry-level fixed vinyl to $1,100–$2,400 for custom arched wood; retrofits cost more when headers or masonry need modification.

I used to overlook the slim pane above a door until I learned it had a name. A transom window. Now I spot them everywhere and I love the charm they add.

A transom window sits above a door or a larger window. It brings in extra light and can boost airflow if it opens. Some are fixed and purely decorative. Others swing or tilt to vent a room. Either way they make a space feel brighter and taller without major changes.

I’ll show you what sets transoms apart from other windows and where they work best. If you want more light style and a simple upgrade you’ll want to know how these little panes punch above their weight.

What Is A Transom Window?

A transom window is a slim glazed panel set above a door or another window to add daylight and sometimes airflow. Source: Andersen Windows glossary https://www.andersenwindows.com/ideas-and-inspiration/window-and-door-glossary and Pella guide https://www.pella.com/ideas/windows/transom-windows

Placement: Directly above the door head or window head across the opening
Shape: Usually horizontal and narrow with a rectangular or arched profile
Operation: Fixed or operable with hinged or awning action for ventilation
Purpose: Daylighting and ventilation plus visual height and proportion
Styles: Rectangular, arched, fanlight with divided lites or single lite
Materials: Wood, fiberglass, aluminum, vinyl frames with insulated glass
Privacy: Clear, frosted, or textured glass for entry or bath use
Compatibility: Exterior entries and interior passages across traditional and modern homes

I use transom window as the everyday term and I note overlight for British usage and fanlight for arched forms. Source: Oxford Reference architecture https://www.oxfordreference.com/display/10.1093/oi/authority.20110803100445954

Table: Common door context for a transom window

Element	Typical value
Standard interior door height	80 in
Tall door height	96 in

Source: Home Depot door size guide https://www.homedepot.com/c/ab/standard-door-size-guide/9ba683603be9fa5395fab90a9b8f3c2

Types And Styles

I group transom window types by how they operate, what they’re made of, and how they look. I match style to function first, then I layer in shape and detailing.

Fixed Vs. Operable

I pick fixed for pure daylight and clean sightlines, and I pick operable for airflow and stack ventilation above a door.

Fixed: Clean edge-to-edge glass that maximizes light and reduces lines, good above exterior doors that already swing.
Operable: Hinged or pivoted sash that opens a few inches for ventilation, common as awning or hopper actions.
Placement: Interior or exterior locations that want light at the top of the wall, with exterior installs meeting safety glazing near doors per IRC R308.

Materials And Shapes

I match materials to exposure and maintenance, and I match shapes to the architecture.

Wood: Warm profile that takes paint or stain, best when protected by an overhang, source Marvin size and species options.
Fiberglass: Stable frame that resists warping in sun and heat, source Pella fiberglass lines.
Aluminum: Slim sightlines in modern facades with thermal breaks, source Andersen commercial frames.
PVC: Low maintenance frame for humid baths or coastal zones, source Pella vinyl lines.
Rectangle: Classic transom window shape that spans a door head, seen in 1-lite or multi-lite layouts.
Arch: Curved fanlight form that softens entries in traditional homes, also called a fanlight in British usage.
Segmental: Low-rise arch that fits standard door widths without raising the header.
Circle: Ocular accent that tops a window wall or stair landing for a focal point.

Decorative And Grille Options

I add pattern and privacy with glass makeup and grille types.

Grilles-between-glass: Easy-clean bars sealed between panes, offered in 3/4 in and 1 in profiles, source Andersen and Pella catalogs.
Simulated divided lites: Applied exterior and interior bars with spacer for a true-divided look, used on historic facades.
True divided lites: Individual small panes in wood or steel sash, used in preservation projects.
Leaded glass: Decorative cames with clear or textured pieces, used for period entries.
Textured glass: Reeded, frosted, or seedy options that diffuse views while keeping daylight, used in baths or street-facing doors.
Low-E coatings: High-performance layers that cut solar heat gain while keeping visible light, verified by NFRC labels.

Spec	Typical Range	Context	Source
Transom height	10–16 in	Above doors and windows	Marvin Window Size Charts 2024
Transom width	24–72 in	Spans single to double doors	Pella Architectural Design Manual 2023
Operable sash opening	3–5 in	Awning or hopper ventilation gap	Andersen Product Guides 2024
Grille profile thickness	0.75–1.00 in	GBG and SDL bar dimensions	Pella and Andersen Catalogs
Safety glazing	Tempered	Within 24 in of door edge per code	International Residential Code R308

Sources: Marvin Window Size Charts 2024, Pella Architectural Design Manual 2023, Andersen Windows Product Guides 2024, International Residential Code R308 (2021).

Benefits And Drawbacks

Transom windows add daylight and airflow above doors or larger windows. They also introduce tradeoffs in privacy, noise, energy, and security.

Natural Light And Ventilation

Add daylight, transom window placement high on the wall delivers diffuse light that reaches deeper into a room, clear double glazing often transmits 60% to 75% visible light per NFRC VT ratings, source, National Fenestration Rating Council.
Boost height perception, a transom window draws the eye upward which makes walls feel taller without structural changes.
Reduce glare risk, a narrow over-door opening softens contrast compared to a full-height window, low-e coatings cut solar heat gain while maintaining VT, source, U.S. DOE.
Enable passive airflow, operable transom sashes promote crossflow and stack effect ventilation when placed above doors, ASHRAE 62.1 permits natural ventilation when openings equal at least 4% of floor area, source, ASHRAE 62.1.
Limit energy loss, fixed transoms avoid air leakage from operable hardware, insulated glazing and low-e coatings improve U-factor and SHGC, source, Energy Star.

Table, performance touchpoints

Aspect	Typical Value	Context	Source
Visible Transmittance	0.60–0.75	Clear double glazing	NFRC
Natural Ventilation Opening	≥4% of floor area	Eligibility threshold	ASHRAE 62.1
Air Leakage, operable	0.1–0.3 cfm/ft²	Product-rated range	NFRC product database

Privacy, Sound, And Security

Preserve privacy, a high transom window limits direct sightlines from outside, obscure glass and textured lites add screening in bathrooms and entry halls, source, International Residential Code R308 glazing types.
Dampen noise, laminated glass adds a polyvinyl interlayer that increases Sound Transmission Class by roughly 3 to 5 points compared to tempered glass of the same thickness, source, ASTM E413, PNNL acoustic glazing briefs.
Manage security, laminated interlayers resist forced entry longer than monolithic glass which supports UL 972 burglary-resistant glazing design, source, UL 972.
Meet safety glazing, transom windows within hazardous locations or near doors often require tempered or laminated safety glass, CPSC 16 CFR 1201 defines impact standards, source, CPSC.
Accept tradeoffs, obscure textures reduce VT compared to clear glass, laminated panes increase cost and weight which affects hardware selection.

Table, privacy and protection touchpoints

Aspect	Typical Impact	Context	Source
STC Gain, laminated vs tempered	+3 to +5	Same thickness comparison	ASTM E413, PNNL
Safety Glazing Standard	16 CFR 1201	Impact test for doors and adjacent glazing	CPSC
Burglary-Resistant Glazing	UL 972	Delay against forced entry	UL

I weigh these factors by room role, door usage, climate, and code scope, then I size the transom window and select glazing to match the target outcome.

Design And Placement Considerations

I match transom window design to the room program and the adjacent opening. I then place the unit to balance daylight, airflow, and privacy.

Above Doors Vs. Above Windows

I start with the opening type because door and window transoms do different jobs.

Favor above doors for airflow in halls and entries when I use operable sashes like hopper or awning. Stack effect pulls warm air up and out when vents sit high, then low openings feed cool air in (DOE Energy Saver).
Favor above doors for borrowed light in interior corridors when rooms lack exterior walls. Obscure glass keeps privacy in bedrooms and baths.
Favor above windows for deeper daylight penetration in living rooms and kitchens. High glazing pushes diffuse light farther across floors and worktops (DOE Energy Saver).
Favor above windows for view control when I cap tall furniture like bookcases. Clear glass adds sky view while base windows handle eye level.
Align mullions with door stiles or window jambs for clean sightlines. I keep head and transom frame lines consistent across a wall.

Recommended clearances and sizes

Location	Vertical gap above frame	Transom height	Transom width relation
Above exterior door	2–6 in	10–18 in	Match door unit width
Above interior door	1–4 in	8–14 in	Match door slab width
Above window	1–6 in	8–16 in	Match window unit width

I use safety glazing near doors and in hazardous locations per code if impact risk exists. Codes list doors and adjacent panels within 24 in as hazardous locations (IRC R308.4, 2021).

Ceiling Height, Proportions, And Sightlines

I scale the transom window to ceiling height so the wall reads balanced.

Keep head heights aligned across a room. Match the transom head to the primary door or window head for order.
Keep transom height at 15–25% of the combined opening when ceilings are 8–10 ft. I move toward 10–15% in rooms 10–12 ft high to avoid top heaviness.
Keep the transom sill 6–12 in below the ceiling plane in standard rooms. Tight gaps reduce glare and boost uniformity.
Keep muntin and grille patterns aligned with lower lites. I mirror vertical divisions for symmetry in pairs like double windows.
Keep frame depths flush with casing or drywall returns. Flush planes simplify shadows and reduce visual clutter.

Proportion guide

Ceiling height	Opening below transom	Transom height target	Gap to ceiling
8 ft	80–84 in	10–16 in	6–10 in
9 ft	84–90 in	10–18 in	6–12 in
10–12 ft	90–96 in	12–20 in	8–12 in

I confirm tempered or laminated glass when the transom sits near doors or stair landings per code constraints (IRC R308.4, 2021). I verify U-factor and SHGC ratings to manage heat gain in sun zones per climate data (DOE Energy Saver).

Historic Vs. Modern Aesthetics

I tune the transom window language to the architecture so the detail feels native.

Match historic forms with true divided lites, narrow wood stiles, and arched fanlights in Federal and Georgian homes. Leaded or beveled glass fits Craftsman and Victorian entries (NPS Preservation Briefs).
Match historic hardware with surface bolts, cast brass stays, and chain operators on operable sashes. Dark patinas read authentic.
Match modern forms with frameless returns, slim aluminum or fiberglass frames, and clear IGUs. No grilles keeps the plane quiet.
Match modern performance with low-e coatings, laminated interlayers for sound, and thermally broken frames in metal systems. NFRC labels confirm ratings.
Bridge eras with simple rectangular transoms in painted wood for transitional spaces like 1920s bungalows. Reeded or satin-etch glass provides privacy without pattern fuss.

I align material choices to context and maintenance. I pick durable fiberglass or aluminum in humid baths and kitchens, then reserve stained wood for protected entries and living rooms with low moisture exposure (DOE Energy Saver, NPS Preservation Briefs).

Installation And Retrofits

I install a transom window to add daylight and airflow without major disruption. I match the method to the project type and the wall construction.

New Construction Vs. Remodels

I integrate a transom window during framing in new builds. I coordinate the door head height and the transom rough opening to keep sightlines clean.

Plan the unit as one assembly above a door in examples like prehung door plus transom frame
Align the transom mullion with the door jambs for a tight reveal
Frame the rough opening with king studs and jack studs on both sides
Size the header per span and load per IRC R602.7
Flash the head and jambs per ASTM E2112 for water control
Air seal the perimeter with low expansion foam and backer rod
Insulate the cavity above the header to reduce heat loss
Trim the interior and exterior to match existing profiles

I phase a retrofit to control risk in remodels. I verify structure and utilities before I cut.

Survey the wall for utilities in examples like wiring and plumbing
Confirm load paths and bearing points before header changes
Add a new header above the door if the opening grows
Use a steel angle lintel in masonry in examples like brick veneer
Order the transom to the rough opening plus 0.5 in clearance
Insert a factory mulled unit to simplify fit and finish
Flash the exterior with peel and stick membrane and a head flap
Weatherstrip operable transoms to limit infiltration

Structural And Code Considerations

I check structure first. I select a header that carries roof or floor loads and meets span tables.

Calculate the clear span above the door transom assembly
Select header size per IRC R602.7 in examples like 2×10 SPF for a 4 ft span in one story
Add double jack studs at each side for larger spans
Anchor into solid framing and not into shims
Use a continuous steel lintel in solid masonry

I meet glazing safety rules. I place safety glass where code requires it.

Specify tempered or laminated glazing near doors per IRC R308.4.2
Use safety glazing within 24 in of a door edge and within 60 in of a wet area
Choose laminated glass for added security and noise control

I manage energy and moisture. I select rated glass and I detail the opening to drain.

Target ENERGY STAR U factor and SHGC for the climate zone
Air seal the rough opening to DOE Air Sealing guidelines
Slope the sill pan to the exterior for drainage
Flash the head to lap over the side flashings

I consider ventilation and egress. I count operable transom area if the room uses natural ventilation.

Provide net openable area of at least 4 percent of floor area per IRC R303 when used
Exclude transoms from egress sizing in bedrooms in most cases per IRC R310
Keep fire separation intact at a garage door where transoms are not permitted per IRC R302.5

I verify accessibility and hardware in commercial work. I coordinate with IBC and ADA routes.

Maintain required egress ratings and head clearances above doors
Use closers and actuators that do not obstruct the transom swing

Key specs and triggers

Topic	Typical Value or Rule	Example or Source
Transom height	10–18 in	Residential interior hall doors
Rough opening clearance	0.5 in total	0.25 in each side for shimming
Header example	2×10 SPF No.2 for 4 ft span one story	IRC R602.7 tables
Safety glazing near doors	Required if within 24 in of vertical edge and lower edge below 60 in	IRC R308.4.2
Natural ventilation	4 percent of floor area operable	IRC R303
Garage separation	No glazing above garage entry door to dwelling	IRC R302.5
Flashing standard	Follow pan jamb head sequence	ASTM E2112
Energy ratings	Zone specific U factor and SHGC targets	ENERGY STAR Windows

International Residential Code 2021 and 2024 editions. Sections R602.7, R303, R308.4, R302.5. International Code Council
ASTM E2112 Standard Practice for Installation of Exterior Windows Doors and Skylights. ASTM International
ENERGY STAR Most Efficient Window criteria. U.S. EPA and DOE

Cost, Sizing, And Energy Efficiency

I break down cost, sizing, and energy metrics for a transom window. I match numbers to common product choices and code backed terminology.

Pricing Factors And Budget Ranges

I price a transom window by material, size, operation, glazing, and labor.

Material: Vinyl runs $120–$350, aluminum runs $200–$600, fiberglass runs $300–$800, wood runs $250–$700.
Size: Small spans of 24–36 in wide by 10–14 in high fall at the low end, larger spans of 48–72 in wide by 14–24 in high add 15–40%.
Operation: Fixed frames add $0 in hardware, operable sash adds $150–$400 for hinges, stays, or electric openers.
Shape: Standard rectangles price lowest, curved or arched units add $200–$800 for custom fabrication.
Glazing: Tempered or laminated safety glass adds $50–$200, low‑e coatings add $20–$60 per unit, gas fill adds $10–$30.
Labor: New construction install runs $150–$400, retrofit cut‑in runs $300–$900 depending on wall finish and header changes.

I group typical totals for a single transom window.

Configuration	Size Range (in)	Material	Operation	Glass	Unit Cost (USD)	Install (USD)	Typical Total (USD)
Entry level fixed	24–36 x 10–14	Vinyl	Fixed	Clear tempered	120–300	150–400	270–700
Mid range fixed	36–60 x 12–18	Fiberglass	Fixed	Low‑e tempered	300–700	200–600	500–1,300
Operable upgrade	36–60 x 12–18	Aluminum	Hinged	Low‑e tempered	400–800	300–700	700–1,500
Custom arch	48–72 x 14–24	Wood	Fixed	Low‑e laminated	700–1,500	400–900	1,100–2,400

I cite cost bands from national retailer catalogs and trade pricing guides for residential fenestration, then I align installation ranges with Remodeling Magazine Cost vs Value reports and contractor averages for 2023–2025.

U-Factor, SHGC, And Glazing Choices

I define the core ratings for a transom window using NFRC terms. U‑factor measures heat transfer, lower values insulate better. SHGC measures solar heat gain, lower values block more sun. VT measures visible light, higher values transmit more daylight. Air Leakage measures airflow at 0.3 cfm/ft² or less for typical rated products. Sources: U.S. Department of Energy, National Fenestration Rating Council, ENERGY STAR.

Metric	Typical Range	What It Means	Source
U‑factor	0.25–0.35	Lower reduces conductive heat loss	DOE, NFRC
SHGC	0.20–0.55	Lower reduces solar heat gain	DOE, NFRC
VT	0.40–0.70	Higher increases daylight	NFRC
Air Leakage	≤0.3 cfm/ft²	Lower reduces drafts	NFRC

I match glazing builds to performance targets.

Double pane low‑e: Delivers U 0.27–0.32, delivers SHGC 0.25–0.45, delivers VT 0.45–0.65, suits most climates per DOE guidance.
Triple pane low‑e: Delivers U 0.15–0.23, delivers SHGC 0.20–0.40, delivers VT 0.35–0.55, suits cold zones that prioritize heat retention.
Low‑e type: Soft‑coat low‑e boosts U‑factor gains, hard‑coat low‑e boosts solar gain in sunny cold climates, per DOE window selection guidance.
Gas fill: Argon fill lifts U‑factor by about 0.02–0.03, krypton fill lifts further at higher cost, per NFRC data.
Spacer: Warm edge spacers trim condensation risk and edge losses, per NFRC technical bulletins.
Safety layer: Laminated glass increases impact resistance and sound control, tempered glass meets safety near doors per IRC R308.

I map climate aims to rating targets using ENERGY STAR and DOE guidance. Cold climates favor U ≤0.27 and SHGC 0.35–0.55 for passive solar spaces. Mixed climates favor U 0.25–0.30 and SHGC 0.25–0.40. Hot climates favor U 0.25–0.30 and SHGC 0.20–0.30. Sources: ENERGY STAR Certified Windows Criteria, DOE Efficient Windows.

Maintenance And Longevity

I protect a transom window by keeping water out, keeping parts moving, and keeping finishes intact. I set a simple schedule, then I track tasks by season.

Cleaning, Sealing, And Hardware Care

Inspect glazing, frame joints, weatherstrips, and sill pan each spring, each fall, and after storms for gaps or cracks for air and water control sources DOE, FGIA.
Clean glass with mild soap, water, and a soft cloth, avoid abrasives on low‑E coatings for clarity and coating life sources DOE, FGIA.
Wash frames using the material match, wood with mild soap, fiberglass with nonabrasive cleaner, aluminum with neutral pH, PVC with diluted dish soap for finish retention sources FGIA, Pella.
Lubricate hinges, stays, and locks with dry Teflon or silicone spray, avoid petroleum on vinyl or dust‑prone areas for smooth operable action sources Andersen, FGIA.
Reseal exterior perimeter with ASTM C920 sealant at 10 to 15 year intervals, spot repair sooner where cracks appear for bulk water defense sources ASTM, FGIA.
Replace compressible weatherstripping when flattened or brittle, typically 5 to 10 years, for airtight and weathertight performance sources DOE, FGIA.
Repaint or refinish wood exteriors every 3 to 5 years in sun, 5 to 7 years in shade, sand lightly between coats for UV and moisture protection sources USDA FPL, Marvin.
Clear weep holes and head flashing paths each season, use a plastic pick, confirm free drainage for moisture management sources FGIA.

Maintenance intervals

Task	Interval	Notes
Inspection cycle	2 times per year	Add after extreme weather
Glass cleaning	4 to 6 times per year	Use soft water where hard water spotting occurs
Hardware lubrication	1 time per year	Increase to 2 for coastal zones
Sealant check	1 time per year	Full reseal at 10 to 15 years
Weatherstrip replacement	5 to 10 years	Replace sooner if compression set >30%
Wood finish renewal	3 to 7 years	Shorter in south, longer in north
Drainage path clearing	2 times per year	Spring, fall

Common Issues And Fixes

Drafts enter at the transom window perimeter, replace worn weatherstrips, add backer rod and C920 sealant to gaps over 6 mm for tightness sources DOE, FGIA.
Condensation forms on interior glass in winter, reduce indoor RH to 30 to 40 percent, increase air mixing with the door open briefly, upgrade to low‑E with warm‑edge spacer for higher surface temps sources DOE, LBNL.
Water stains show at the head jamb, verify head flashing with end dams, reflash with self adhered membrane and metal drip edge, clear clogged weeps for drainage control sources IRC R703, FGIA.
Sash binds on operable transoms, adjust hinges or stays, shim keepers, tighten loose screws with longer fasteners into framing for smooth action sources Andersen, Pella.
Paint peels on exterior wood, remove failed film to bare wood, spot prime with alkyd or acrylic primer, apply 2 coats of exterior acrylic latex for durability sources USDA FPL.
Sealant cracks at masonry joints, use backer rod and a tooled hourglass bead of ASTM C920 class 25 sealant for movement capability sources ASTM.
Glass rattles in the transom window stop, replace glazing points or setting blocks, add a thin glazing tape for firm seating sources FGIA.
Noise increases after retrofits, switch to laminated IGU, 6.5 mm to 8.8 mm interlayered glass, improve STC and security together sources LBNL, DOE.

Sources: U.S. Department of Energy Windows and Doors, FGIA Care and Maintenance Guide, IRC R703, LBNL Windows, ASTM C920, USDA Forest Products Laboratory Wood Handbook, Andersen, Pella, Marvin.

Alternatives And Comparisons

I compare transom window options with nearby cousins that solve light and airflow in different ways. I keep placement and code in view so choices stay practical.

Clerestory Windows And Sidelights

I frame clerestories as high-wall daylighting and sidelights as vertical door companions around a transom window.

Placement: Clerestory sits near the ceiling plane, sidelight flanks the door jamb.
Daylight: Clerestory sends deeper ambient light, sidelight brightens the entry plane.
Privacy: Clerestory protects sightlines in baths and bedrooms, sidelight exposes unless frosted.
Ventilation: Clerestory can vent with awning sashes, sidelight rarely vents.
Energy: Clerestory can cut glare and raise daylight autonomy, sidelight adds perimeter gain.
Safety: Clerestory sits outside hazardous zones, sidelight near doors follows safety glazing rules.
Style: Clerestory aligns with modern facades, sidelight pairs with classic entries.

I match quick specs for a transom window against clerestories and sidelights.

Feature	Transom Window	Clerestory Window	Sidelight
Typical sill height	80-96 in above floor	84-120 in above floor	0-12 in above floor
Typical width	24-72 in	24-144 in	8-18 in
Typical height	10-20 in	12-36 in	36-84 in
Vent area ratio	0-40% of unit area	0-60% of unit area	0-10% of unit area
Safety glazing near doors	Required within 24 in of door edge and bottom edge below 60 in	Not required if outside hazardous zones	Required within 24 in of door edge and bottom edge below 60 in
Light distribution	High bounce and low glare	Deep daylight penetration	Entry accent and view

Sources: 2021 IRC R308 for safety glass near doors, 2021 IRC R303 for ventilation, NFRC 500 for vent area definitions, IES Lighting Handbook 10th for daylight patterns.

Materials: Clerestory frames use aluminum and fiberglass, sidelights use wood and PVC, transoms use all four examples.
Glazing: Clerestory favors low SHGC in hot zones, sidelight favors laminated for security, transom favors low U and obscure for privacy.
Security: Sidelight invites forced entry risk next to locks, clerestory and transom reduce reach risk.

Skylights And Interior Transoms

I contrast roof skylights and interior transoms with a transom window over doors or exterior windows.

Placement: Skylight sits on roof planes, interior transom spans above interior doors.
Daylight: Skylight delivers 3-5x the daylight of same-size vertical glazing, interior transom relays light between rooms.
Heat gain: Skylight raises solar gain without exterior shading, interior transom adds no solar gain.
Ventilation: Skylight vents buoyant air at the top, interior transom moves air between rooms only.
Moisture: Skylight needs curb flashing at roof, interior transom avoids exterior water.
Safety: Skylight uses laminated or tempered overhead glass, interior transom follows corridor egress widths.
Acoustics: Skylight adds rain noise, interior transom shares sound between rooms.

I stack core metrics for a transom window against skylights and interior transoms.

Feature	Transom Window	Skylight	Interior Transom
Daylight factor gain	0.5-2% in adjacent zone	2-5% in adjacent zone	0.5-1% in receiving room
SHGC target warm climates	≤0.28	≤0.25	N/A
U-factor target cold climates	≤0.30 Btu·h⁻¹·ft⁻²·°F⁻¹	≤0.40 Btu·h⁻¹·ft⁻²·°F⁻¹	N/A
Operable share	0-40% of units	0-50% of units	0-20% of units
Safety glazing	Required in hazardous locations	Required overhead	Not required unless near doors
Leak risk	Low with head flashing	Higher without curb and step flashing	None from exterior

Sources: ENERGY STAR 2023 criteria for U-factor and SHGC by zone, NFRC 100 for rating methods, IES LM-83 for daylight metrics, 2021 IRC R308 for safety glass, 2021 IRC R903 for roof flashing.

Use cases: Skylights suit interior baths and halls, interior transoms suit dark corridors and studies, transoms suit entries and living rooms.
Controls: Skylights pair with blinds and rain sensors, interior transoms pair with privacy glass, transoms pair with operable sashes.
Retrofits: Skylights require roof work and permits, interior transoms fit non load bearing walls, transoms fit door replacements and window remodels.

How To Choose The Right Transom Window

I match the transom window to the room purpose and the adjacent opening. I balance daylight, airflow, privacy, and energy.

Matching Architecture And Materials

Match proportions to the host opening for cohesion. Match a single front door with a rectangular transom. Match a pair of French doors with a wider multi-lite transom. Match an arched entry with a segmental or full arch transom.
Match profiles to the style for continuity. Match classic trim with wood or clad wood. Match modern lines with aluminum or fiberglass. Match coastal settings with PVC or fiberglass.
Match glass to performance for comfort. Match low E double pane for temperate zones. Match low E triple pane for cold zones. Match laminated glass for sound and security.
Pick an operation for function. Pick fixed for maximum light and lowest air leakage. Pick operable for stack ventilation above a door or window.
Pick finishes for maintenance. Pick factory paint or anodized finishes for low upkeep. Pick stain grade wood for historic millwork.
Choose grilles for context. Choose true divided lites for period homes like Craftsman and Colonial. Choose simulated lites for energy performance. Choose no grilles for contemporary entries.
Choose sightlines for privacy. Choose clear glass in public spaces with high mounting. Choose obscure glass in baths and bedrooms. Choose tinted glass on sun exposed facades.

Measuring And Working With Pros

I confirm the structure, then I measure the opening.

Measure the door or window unit first. Measure frame width and head height. Measure jamb depth for trim alignment.
Measure the available head space next. Measure from the top of the frame to the ceiling or soffit. Measure any crown or casing.
Measure for rough opening last. Measure wall thickness and header span. Measure space for insulation and shims.

Item	Typical range	Notes
Transom height	10–18 in	12 in reads balanced above a 80 in door
Transom width	Match unit below	Align stiles and mullions
Head clearance to ceiling	2–8 in	Keep at least 2 in for trim returns
Rough opening adders	+1/2–3/4 in	Allow for shims and plumb
Operable clearance	+2 in height	Space for hardware throw

Coordinate structure with a contractor. Coordinate header sizing over combined spans. Coordinate placement of the mull to carry loads.
Coordinate codes with a designer. Coordinate safety glazing near doors and wet areas. Coordinate egress and ventilation targets where applicable.
Hire certified installers for warranty. Hire a pro with factory training on the brand. Hire a glazier for large insulated units.
Verify shop drawings before order. Verify sightlines, profiles, and sill details. Verify hinge swing on operable transoms.

Conclusion

I hope this guide nudged you to see your openings with fresh eyes. When design meets purpose small choices can shape how a room feels every day. If your space is asking for a gentle lift a transom could be the note that ties everything together.

Sketch a few options take measurements and gather photos you love. Then talk with a trusted pro and align on budget timeline and code. I like to sleep on final picks for a day. If it still feels right go for it and enjoy the glow.

Frequently Asked Questions

What is a transom window?

A transom window is a slim glazed panel installed above a door or another window. It brings in extra daylight and, if operable, adds passive ventilation. Transoms can be rectangular or arched, fit traditional or modern homes, and help rooms feel taller and brighter without major renovations. In everyday usage it’s “transom,” while “overlight” is common in the UK and “fanlight” often refers to arched styles.

Are transom windows operable or fixed?

Both options exist. Fixed transom windows maximize daylight, maintain clean sightlines, and typically offer better energy performance. Operable transoms open to release warm air and improve airflow between rooms or to the exterior. Choose fixed for efficiency and simplicity; choose operable where ventilation and seasonal comfort are priorities, like hallways, bathrooms, mudrooms, and above exterior doors.

Do transom windows improve ventilation?

Yes, operable transom windows act as high vents that let hot air escape and draw in cooler air from lower openings. This stack effect supports passive cooling and can reduce reliance on mechanical systems. For best results, pair an operable transom with an openable window or door, and consider insect screens and secure hardware for nighttime ventilation.

How do transom windows affect privacy?

High placement preserves privacy while admitting light. For extra privacy, choose obscure, frosted, textured, or laminated glass. Decorative grilles or divided lites can also soften views. In bathrooms or street-facing rooms, use privacy glazing with a low U-factor and appropriate SHGC to balance light, efficiency, and comfort.

What materials are best for transom windows?

Common materials include wood (warm, classic, higher maintenance), fiberglass (durable, efficient, low maintenance), aluminum (slim profiles, modern, good for large spans), and PVC/vinyl (budget-friendly, low maintenance). Match the frame material to your home’s style, exposure, and maintenance tolerance. Use corrosion-resistant finishes in coastal areas.

How much do transom windows cost?

Pricing varies by size, shape, material, glazing, and operation:

Entry fixed vinyl units: roughly $150–$400
Mid-range fiberglass or aluminum: $400–$1,000
Operable units: add $200–$600
Custom arches or stained glass: $1,000–$3,000+
Installation/labor: $200–$1,200+ depending on structural work
Energy-efficient glazing and complex shapes increase costs.

Are transom windows energy efficient?

They can be. Efficiency depends on glazing and frame. Look for low U-factor (insulation) and climate-appropriate SHGC (solar heat gain). Low-E, double or triple glazing, warm-edge spacers, and proper weatherstripping help. Fixed transoms usually outperform operable ones. In hot climates, lower SHGC reduces heat gain; in cold climates, moderate SHGC captures winter sun.

Do transom windows require safety glazing?

Yes, in certain locations. If the transom is within hazardous zones (such as near doors, stair landings, or in wet areas) or if glass extends to specific heights, tempered or laminated safety glazing may be required by code. When in doubt, consult local building codes or a licensed contractor to confirm glazing requirements.

Can I retrofit a transom above an existing door?

Often, yes. A retrofit may require reframing, a new or upsized header, and trim adjustments. Verify structural loads, wiring, and clearances. Use a properly flashed unit to prevent leaks, meet energy codes, and choose safety glazing if required. Hire a qualified installer to maintain structural integrity and warranty coverage.

What size should a transom window be?

Typical heights range from 8 to 18 inches, with width matching the door or window below. Maintain proportional sightlines and head heights across a room. In 8–9 foot ceilings, keep slimmer profiles; with taller ceilings, you can go larger or add arched shapes. Ensure enough space for headers, casing, and any operable hardware.

How do transoms compare to clerestory windows?

Clerestory windows sit near the roofline and bring deep daylight into large spaces, often on high walls. Transom windows sit just above doors or windows, adding light and ventilation without major structural changes. Choose clerestory for expansive daylighting and privacy in tall rooms; choose transoms for subtle height, light, and airflow over openings.

How do transoms compare to skylights?

Skylights bring overhead light and potential heat gain; they’re great for interior rooms without exterior walls. Transoms bring lateral light with lower moisture and heat-gain risks. Operable transoms can ventilate without roof penetrations. Pick skylights for maximum top light; pick transoms for balanced daylight, easier maintenance, and simpler installation.

Are transom windows secure?

Yes, with the right choices. Fixed units are inherently secure. For operable transoms, choose laminated glass, robust locks, and quality hardware. Laminated interlayers resist forced entry and dampen sound. Proper installation, anchored frames, and compatible security sensors further enhance protection.

What styles work with transom windows?

Almost any. Use clean-lined frames and simple grilles for modern homes; divided lites, arches, or stained glass for traditional or historic styles. Match frame material, profiles, and sightlines to adjacent doors and windows for a cohesive look, and align head heights and mullion lines across elevations.

How do I maintain transom windows?

Seasonally, clean glass and frames, inspect and reseal joints, and replace worn weatherstripping. For operable units, lubricate hinges and locks, tighten fasteners, and check screens. Address condensation with better ventilation and consider upgrading to low-E or laminated glazing if moisture or noise is persistent. Prompt maintenance extends lifespan and performance.

What energy ratings should I look for?

Check the NFRC label. Key metrics:

U-factor: lower is better for insulation.
SHGC: lower in hot climates; moderate in cold.
Visible Transmittance (VT): higher for more daylight.
Air Leakage (AL): lower for tighter units.
Choose ratings that suit your climate and room orientation.