A transom window is the glass above a door or another window, and replacing one is usually a smaller job than replacing a full window. It is also easy to get wrong. The right choice depends on what has failed: the glass, the sash, the frame or the wall around it. Replace only the part that failed, and you save money. Replace the wrong part, and you pay twice.
This guide covers how to diagnose the problem, the three ways to fix it, what moves the price, the code and water-management issues that catch people out, and how to get a quote you can trust. We install and repair windows, doors and glass across the Kansas City area, so the examples come from that kind of work.
TL;DR
- Cracked or fogged glass in a sound frame usually needs new glass only, not a new window.
- Rot, a bent frame or a failed seal at the wall means the whole transom unit, and sometimes the framing, must come out.
- Transoms sit above doors, so safety glazing rules may apply. Ask your installer to check them before ordering glass.
- Price depends on size, shape, glass type, access and hidden damage. Anyone quoting a firm number without seeing the opening is guessing.
- Flashing matters more than the window brand. A well-made unit installed badly will still leak.
Table of Contents
- What counts as a transom window
- Start with the diagnosis: what actually failed
- Your three options
- What drives the cost
- Code and safety glazing: the part people skip
- Flashing and fit: why installation matters more than the label
- Energy performance: what to expect and what to compare
- How we think about transom jobs
- How to get an accurate quote
- Residential and commercial transoms
- Get your transom looked at
- FAQ
- Sources
What counts as a transom window
A transom is a window set above a door, or above another window, in the same opening. Some are fixed panes. Others open on a hinge or a crank. Shapes vary: rectangular strips over a front door, half-rounds, and arches. You will find them in older brick homes, in bungalows with leaded or patterned glass, in newer homes where a builder wanted light over a tall entry, and in commercial storefronts above the door.
That variety is why “transom replacement” covers very different jobs. A plain rectangular vinyl unit over a patio door is quick. A custom arch in a brick wall is not. You can see what the second kind involves in our arched transom window installation on a brick exterior.
Start with the diagnosis: what actually failed
Before you call anyone, spend ten minutes looking at the transom from inside and outside. Use a flashlight and a screwdriver.
Glass problems
- Cracked or broken pane. If the frame is straight and solid, the glass can often be replaced alone.
- Fog or moisture between panes. This means the seal on a double-pane unit has failed. The frame may be perfectly fine. See our page on foggy glass replacement for how we handle it.
- Scratched, etched or discolored glass. Usually cosmetic, but on older units it can point to a failed coating or an old film.
Frame and sash problems
- Soft wood. Press a screwdriver tip into the sill and the lower corners. If it sinks in, you have rot. Rot does not stay put, and new glass in a rotten frame is wasted money. Our window frame rot repair and replacement page explains how we deal with it.
- Sash that will not latch or open. On an operable transom, the cause may be worn hardware rather than the window. Replacement hardware is a much cheaper fix than a new unit.
- Daylight around the edge or drafts. Failed caulk, missing weatherstripping or a shifted frame.
Wall and water problems
- Stains on the drywall or trim above the transom. Water has been getting in, maybe for years. The window may not be the source. Flashing, siding or a roof detail could be.
- Bulging or cracked brick mortar around an arch. Have this looked at before anything is ordered.
A good installer will look at the same things. If someone quotes a transom replacement without opening the trim or checking the sill, treat that quote as a rough guess.
Your three options
| Option | Best when | What it does not fix |
|---|---|---|
| Replace the glass only | Frame is sound, glass is cracked or fogged | Rot, drafts from the frame, bad flashing |
| Repair the frame or hardware | Sash sticks, hardware is worn, minor rot, failed caulk | Failed glass seals, major structural rot |
| Full transom replacement | Frame is rotten or warped, unit is single-pane and failing, opening has water damage | Problems elsewhere in the wall |
Glass-only replacement
This is the cheapest route when it applies. The installer removes the stops or glazing, takes out the damaged pane and fits a new insulated or single pane cut to size. It works well on wood frames in good shape and on many commercial frames. For an overview of what this involves, see our glass replacement services and window glass replacement pages.
Old transoms with decorative, patterned or wavy glass are a special case. Matching the look can take time, and a modern replacement may look different. Decide up front whether you want to preserve the character or modernize.
Repair
Repair makes sense when the damage is limited. Replacing hardware, re-caulking, adding weatherstripping and fixing a small area of rot can all extend the life of a transom by years. It stops making sense when the repair has to be repeated every season.
Be skeptical of quotes that are far below the others. A cheap number can mean the contractor plans a surface patch over damage that needs cutting out. The same principle holds in any trade where hidden decay is involved: a marine repair shop explaining boat transom work makes the same warning about low quotes that hide shallow, temporary fixes on a saturated core. The material is different, but the lesson transfers to a rotted wood window frame.
Full replacement
A full replacement removes the old unit and installs a new one, with new flashing and sealing at the opening. It is the right call when the frame is compromised, when you want a modern double-pane unit in place of single glazing, or when the opening has been repeatedly repaired.
There are two ways to do it:
- Insert (pocket) replacement. The new unit goes inside the existing frame. It keeps the trim and is less disruptive, but it reduces the glass area slightly and only works if the old frame is sound.
- Full-frame replacement. Everything comes out to the rough opening. This costs more but lets the installer inspect and repair the framing and rebuild the flashing.
If you suspect water has been getting in, full-frame is usually the honest answer.
What drives the cost
We do not publish a price for transom replacement because no honest figure exists without measuring the opening. Online averages mix small fixed vinyl units with large custom arches, so they say little about your job. These are the factors that move the number:
- Size and shape. A standard rectangle is cheaper than a half-round or an arch, which is cut or built to order.
- Glass. Single pane, insulated, low-E, laminated or tempered all cost differently. Laminated or tempered glass may be required by code (see below).
- Frame material. Vinyl, wood, fiberglass or aluminum, and whether the unit is stock or custom.
- Height and access. A transom above a tall entry may need scaffolding or a lift.
- Exterior finish. Brick, stucco and siding each need different trim and flashing work. Brick often means more labor.
- Hidden damage. Rot or water-damaged framing is usually found only once the old unit is out. A good estimate lists how that will be handled and priced.
- Operable or fixed. Hinges, cranks or other hardware add parts and labor.
The practical advice: ask for a written estimate that separates the unit, the glass, labor, trim and any allowance for rot. That makes quotes comparable and keeps surprises small.
Code and safety glazing: the part people skip
A transom over a door is close to a place where people walk, and glass near doors is often subject to safety glazing rules. Whether yours is depends on the exact position, the local code and the size of the pane, so we will not give you a blanket rule here. We cover the locations that typically matter in our guide to safety glazing locations.
There is a second reason to be careful. The U.S. Department of Energy’s retrofit guidance notes that code requirements such as safety glazing and egress may have changed since the original window went in, so replacing an old window can mean bringing the opening up to current standards. If the transom is part of a basement or bedroom opening, egress also comes into play; our egress window size guide lists the dimensions inspectors check.
Your city or county building department sets the rules that apply to your address. Call them, or ask your installer which permits and inspections your job needs.
Flashing and fit: why installation matters more than the label
The most common cause of a failed replacement is not the window. It is water getting around it. The DOE’s retrofit guide describes the rain plane as the true boundary between the inner and outer portions of the wall, and says the window flashing has to tie into it. If the flashing is wrong, even an efficient window will not protect the house.
What to ask about:
- Jamb depth. If siding has been added or changed since the original window was installed, the wall may be thicker. The same DOE guide points out that a unit of the wrong depth will fit poorly and be hard to flash and seal.
- Sill pan or sloped sill. Water that reaches the sill should be directed out, not into the wall.
- Flashing sequence. Pieces should overlap like shingles, from the bottom up.
- Sealant and backer rod. Gaps should be filled properly, not just caulked over.
This is also why DIY transom replacement carries more risk than it looks. Swapping a pane in a sound frame is something a handy person can try, though glass above a door is heavy and sharp, and reaching it often means a tall ladder. Replacing the whole unit and rebuilding the flashing is another matter. If you are asking whether you can replace a window yourself, the honest answer is: the glass maybe, the opening probably not.
Energy performance: what to expect and what to compare
A transom is a small piece of your wall, so replacing it will not transform your energy bill. The DOE’s efficiency guidance says that replacing windows solely for energy savings is generally not cost-effective, and that insulation and air sealing usually return more. Durability, comfort and appearance are better reasons to replace. A transom that is failing for those reasons is a good candidate. Swapping a sound one to save energy is not.
When you do choose a unit, compare the NFRC label rather than price alone. ENERGY STAR advises comparing U-factor, solar heat gain coefficient and air leakage, and checking that the product is certified for your climate zone. Our short guide on U-factor versus SHGC walks through reading those numbers. Kansas City has hot summers and cold winters, so both matter.
What about the tax credit?
The federal credit for ENERGY STAR windows was 30% of product cost, up to $600 per year, covering the product and not labor, and only on a principal residence. Under current rules it applied to 2025 installs, not 2026 ones. Read our explainer on the window tax credit and ask a tax professional about your own return before counting on any amount.
How we think about transom jobs
We get calls that start with “I need a new transom” and end with a $99-style fix or a glass swap, and calls that start with “the glass is cracked” and end with a rotten sill. The label on the request rarely matches the real work.
So we start from the opening, not from the product. We look at the frame, press on the sill, check the wall around it and ask what the owner wants: keep the look, improve performance or just stop the leak. Then we say which of the three paths fits, even when that path is the smaller job.
Our view is that most owners are best served by one contractor who can do the glass, the carpentry and the exterior finish. A transom problem often crosses those lines: fogged glass in a frame with rot, or a leaking arch with failing siding. When one company handles all of it, there is no finger-pointing between a glazier and a carpenter, and the estimate covers the whole fix.
One more thing we tell people: do not choose on the lowest number. Choose the quote that says what will be removed, what will be rebuilt and what happens if the old frame turns out worse than it looks.
— Artem
How to get an accurate quote
- Take photos of the transom from inside and outside, plus close-ups of any stains, cracks or soft spots.
- Measure width, height and, if you can, the thickness of the wall. Note whether the transom is fixed or opens.
- Write down the history. Has it leaked, been painted shut, been re-caulked or had the siding changed?
- Ask for a site visit. Pricing a custom shape or a brick opening from photos alone is unreliable.
- Compare itemized quotes. Unit, glass type, labor, trim, flashing and a rot allowance should each be visible.
- Ask about permits and code. Especially for glass above a door.
Residential and commercial transoms
The same logic applies above storefront and office doors, with a few additions: larger panes, aluminum frames, safety and security glass, and the need to keep the entrance working during the job. Property managers handling several units usually want a single point of contact and consistent glass across buildings. We cover that on our pages for commercial storefront doors and windows and commercial window replacement.
Get your transom looked at
If you are in the Kansas City area, we offer free estimates and financing options, and we handle glass, frames, hardware, rot repair and exterior finishing under one roof. See everything we do on our services page, or start at star-ws.com and send us photos of your transom. We will tell you whether it needs new glass, a repair or a full replacement.
FAQ
Can I replace just the glass in a transom window?
Often yes, if the frame is straight, dry and solid. The installer removes the old pane and fits a new one cut to size. If the frame is rotted or the opening leaks, new glass alone will not last.
Is transom window repair better than replacement?
Repair is better when the damage is limited to hardware, caulk, weatherstripping or a small rotten area. Replacement is better when the frame is soft or warped, or when you have already repaired the same spot more than once. An inspection of the sill and frame tells you which.
How much does transom window replacement cost?
It depends on size, shape, glass type, access, the exterior finish and any hidden rot, so a fair price needs a look at the opening. Ask for an itemized estimate that separates materials, labor, glass and a rot allowance. We offer free estimates in the Kansas City area.
Do I need safety glass in a transom above a door?
Possibly. Glass near doors is a common safety glazing location, but the rule depends on the exact position, pane size and your local code. Ask your installer and your city or county building department before ordering the glass.
Can I install a transom window myself?
Swapping a pane in a sound frame is within reach for some experienced DIYers, but the glass is heavy and sits high. Replacing the unit means getting the flashing and sealing right, and the DOE’s guidance puts that at the center of a successful installation. We recommend a professional for anything beyond the glass.
Sources
- Retrofit Best Practices, U.S. Department of Energy
- Energy Efficiency Measures to Incorporate into Remodeling Projects, U.S. Department of Energy
- Residential Windows, Doors and Skylights, ENERGY STAR
- Tax Credits for Windows, Skylights and Doors fact sheet, ENERGY STAR
- What Drives the Cost of a Boat Transom Repair, Harper Marine Services