Hopper and Transom Windows: What They Are and Where the Code Applies

Neither of these is a mainstream replacement window. Hoppers are a small, specialized type, and transoms are an accessory to a door or a larger window. Both come up in older houses, in bathrooms and basements, and whenever someone wants light or air high in a wall.

This page is part of our California window guide. It explains each one and goes through the code points that apply.

Hopper windows

What a hopper is

A hopper has one sash hinged along its bottom edge. Releasing a latch at the top lets the sash tilt into the room, usually limited by a pair of stay arms so that it opens a set distance. Air comes in over the top of the tilted sash.

It is the mirror image of an awning window, which is hinged at the top and pushes out at the bottom. The difference is practical:

Like a casement, a hopper closes by compression: the latch pulls the sash against a gasket. That generally makes for a tighter seal than a sliding sash, though the rated air leakage of the specific product is what counts.

Where hoppers are used

• Basements and crawl-space-level rooms. A short, wide opening just above grade suits a hopper, and nothing swings out into a window well or onto a path. California has fewer basements than most states, but hillside houses in the Bay Area and the foothills often have a lower level cut into the slope.
• Bathrooms. A small hopper high in the wall gives ventilation and privacy together. Pair it with obscure glass.
• Garages, laundry rooms and utility spaces. Anywhere you want a little air and daylight without giving up wall.
• As the operable part of a tilt-and-turn window. A tilt-and-turn in its tilt position is working as a hopper.

Where a hopper is the wrong choice

• Where the sash would tilt into head height over a tub, a counter or a walkway inside the room.
• Where blinds or shutters are wanted. The sash tilts into the space they occupy.
• On a wall that takes driving rain, if you intend to leave it open. An awning is the better type there.
• As a bedroom's only window. See the egress section below.

Transom windows

What a transom is

The transom is the horizontal bar across the top of a door frame. A transom window, or transom light, is the window that sits above that bar. The term is now used more loosely for any short, wide window stacked directly above a door or above a larger window, sharing its width.

A transom can be:

• Fixed, which is what most new ones are;
• Operable as an awning or hopper, as in many houses built before air conditioning, where a transom over each door let warm air move through the house with the doors shut;
• Shaped, such as a half-round or elliptical unit over an entry door. See the special shapes page.

A transom is not the same as a clerestory. A clerestory window is set high in a wall on its own, usually up against the roofline, and is not part of a door or window assembly below it. Mid-century houses use clerestories a great deal, and our Eichler window guide covers them.

Why people want one

• Daylight deep into a room. Light from high in a wall reaches further across the floor than light from a window at eye level.
• Light without loss of privacy. Glass above head height lets in sky, not sightlines.
• Proportion. In a room with a tall ceiling, a standard-height door or window looks squat. A transom fills the wall above it.
• High-level ventilation, if it opens. Warm air collects at the ceiling, and a high opening lets it out while a low opening elsewhere lets cooler air in.

The practical limits

Every opening in a framed wall has a header across the top carrying the load above. A transom has to fit beneath that header. In a house with standard-height ceilings, the header usually sits directly above the door or window, and there is no room for a transom without reframing the opening. In a house with higher ceilings, the header may already be high enough that a transom fits as part of a taller unit.

When a door or window with an existing transom is replaced, there are two ways to order it: as one factory-built unit with the transom integrated, or as two units joined at a horizontal mullion. A factory-built unit keeps the sightlines and finishes consistent and puts one manufacturer behind the joint. Ask which you are being quoted.

An operable transom needs a way to reach it. Old houses used a long rod-and-lever operator. Modern options include a pole-operated latch or a motorized operator, which our sibling page on motorized windows covers. If nobody will ever open it, buy a fixed one.

Code point one: safety glazing

The safety glazing rules are in Section R324 of the 2025 California Residential Code (formerly R308). They are written around locations, and hoppers and transoms tend to sit in or near several of them. Here is how the main triggers apply.

Glass in doors and beside doors

Glazing in the fixed and operable panels of swinging, sliding and bifold doors is a hazardous location (Section R324.4.1). A transom above the door is not part of the door panel.

Glazing adjacent to a door is a hazardous location where its bottom exposed edge is less than 60 inches above the floor and it is within 24 inches of either side of the door, in the plane of the closed door (Section R324.4.2). A sidelite beside an entry door almost always meets this. A transom above a standard-height door does not, because its bottom edge is well above 60 inches.

So in the ordinary case, the transom itself is not required to be tempered by the door rules, while the sidelites and the door glass are. Many manufacturers temper the whole entry assembly anyway, and there is no harm in asking for it.

Wet areas

This is the one that catches bathroom hoppers. Glazing in walls or enclosures containing or adjacent to bathtubs, showers, hot tubs, spas, saunas, steam rooms and pools is a hazardous location where the bottom exposed edge of the glazing is less than 60 inches, measured vertically, above any standing or walking surface (Section R324.4.5). The exception is glazing more than 60 inches, measured horizontally, from the water's edge of a tub or the edge of a shower.

A small window in the wall over a bathtub usually has its bottom edge less than 60 inches above the tub floor, which is a standing surface. It needs safety glazing. Moving the window higher, or further from the tub, can take it outside the rule, but in a small bathroom tempered glass is the simple answer.

Large, low panes

The general window rule in Section R324.4.3 applies only when a pane is larger than 9 square feet, has its bottom edge less than 18 inches above the floor, its top edge more than 36 inches above the floor, and a walking surface within 36 inches. Hoppers and transoms are normally too small and too high to meet it. A basement hopper is the exception to watch if it is large and low.

Stairs

Glazing next to stair flights and landings, with its bottom edge less than 36 inches above the walking surface, is a hazardous location under Sections R324.4.6 and R324.4.7, with exceptions for distance and protective rails. A transom or high window over a stair landing is usually above that height, but a window beside the stair may not be.

Our page on California's tempered glass requirements goes through every location. Safety glazing has to carry a permanent manufacturer's mark, which is what the inspector looks for.

Code point two: egress

Section R319 of the 2025 California Residential Code (formerly R310) requires basements, habitable attics and every sleeping room to have at least one operable emergency escape and rescue opening. The opening must be at least 5.7 square feet net clear, or 5 square feet at a grade floor, at least 24 inches high and 20 inches wide, with the bottom of the clear opening no more than 44 inches above the floor. The dimensions have to result from normal operation of the window, and it must open from inside without keys, tools or special knowledge.

What that means for these two types:

• A transom is never an egress opening. It is far above 44 inches and usually fixed.
• A typical hopper is not one either. It is too small, and a sash that tilts in on limiting arms does not leave the required clear opening.
• Basement bedrooms need a real egress window. If a lower-level room is used for sleeping, each sleeping room needs its own compliant opening. Where the bottom of the opening is below the adjacent ground, the code also requires an area well of minimum dimensions with a ladder or steps once it is deep enough (Section R319.4).
• Not every basement needs one. The code lists exceptions, including basements with no habitable space and not more than 200 square feet of floor area, and rooms with a door opening directly to the outside.

If you are replacing an existing window in the same opening, Section R319.5 lets a replacement stand in for the old one where it is the manufacturer's largest standard size that fits and is the same operating style or one that gives an equal or greater opening. It does not turn a hopper into an escape route. The site's egress window page has the fuller picture, and the building department decides.

Code point three: energy

A hopper or a transom is fenestration like any other window. A replacement has to meet the U-factor and SHGC limits for your climate zone under the 2025 Energy Code, which are set out on what Title 24 requires of replacement windows. Small windows are where the 75-square-foot small-job exception is most often relevant: replacing a bathroom hopper and a couple of other windows is well within it.

Adding a transom where there was none is adding glass area, not replacing it. The energy code handles added fenestration separately from replacement, so tell your contractor early if that is the plan.

Choosing and ordering

• For a bathroom, decide between a hopper and an awning by asking which side has room for the sash, and order obscure, tempered glass.
• For a basement or lower-level room, decide first whether anyone will sleep there. If so, the window is an egress question before it is a style question.
• For a transom, match the frame material, color, glass coating and grille pattern to the unit below. A transom with a different glass tint from the door beneath it is obvious from the street. Our sibling page on window grilles covers pattern matching.
• For an operable transom, settle how it will be opened before you buy it.

For help choosing between operating types more broadly, see how to choose a window style.

Sources

• 2025 California Residential Code, Chapter 3: Section R319 (emergency escape and rescue openings, including area wells and replacement windows) and Section R324.4 (hazardous locations for glazing).
• California Energy Commission, 2025 Building Energy Efficiency Standards.

Working with Heritage Exteriors

We check small bathroom and lower-level windows against the wet-area glazing rule and the egress section before ordering, because these are the ones that get missed. If a transom you want will not fit under the existing header, we will tell you before you pay for one. Licensed in California, CSLB #1055919. Call (916) 546-2991.