A bathroom window next to a tub or shower has to be made of safety glass. That is building code, not a preference, and it turns on two measurements of 60 inches. It settles what you are allowed to order before anybody talks about style. Five things decide the rest. Whether the room needs a window at all, the opening you already have, the type that fits it, the privacy glass, and the frame.
We fit replacement windows across St. Louis and St. Charles County, and bathrooms are the room where the order gets changed most often. The reason is almost always the glass rule below. Read that part first, then the rest is straightforward.
1. The Glass Next to a Tub or Shower
The residential code treats glass near wet surfaces as a hazardous location. Section R308.4.5 covers tubs, showers, hot tubs, saunas and pools. Two measurements decide whether your window is caught by it.
- Height. The bottom exposed edge of the glass sits less than 60 inches above the standing surface. That is the floor of the room, or the floor of the tub if you would be standing in it.
- Distance. The glass is within 60 inches of the water’s edge, measured horizontally in a straight line from the rim of the tub or the edge of the shower.
Where both apply, safety glazing is required and the glass has to be tempered or laminated. Clear past either measurement, and ordinary annealed glass will do. The rule applies to every pane in the unit, not just the one nearest the water.
Glass is the part I check first on a bathroom, because it changes the order rather than the price by much. A tempered unit costs more than an untempered one and it cannot be cut on site. It is made to size at the factory. So a measuring mistake on a tempered window is a reorder, not a trim.
One thing worth knowing: tempered glass breaks into blunt pebbles instead of shards. Laminated glass holds together on a plastic layer. Both satisfy the code. Tempered is what goes into most bathroom orders.
You can check what you already have. Section R308.1 requires every pane of safety glazing to carry a permanent mark, so there is a small etched logo in one corner of the glass. The trade calls it the bug. No bug means the glass is not tempered. Any homeowner can do that themselves in two minutes with a flashlight, and it tells you whether the last person to work on that bathroom got this right.
2. Does a Bathroom Need a Window at All?
People ask this when a bathroom has no window, or when they want to close one up. The code gives you a choice of two, and you only need one of them.
- A window. At least 3 square feet of glass, with at least half of that able to open. Three square feet is 432 square inches, so a unit 24 inches wide by 18 inches tall hits the minimum exactly.
- Or a fan. Mechanical exhaust rated 50 cubic feet per minute if it runs on a switch, or 20 if it runs continuously, ducted to the outside of the house.
The section is IRC R303.3, and the two are alternatives. A bathroom with a working exhaust fan does not legally need a window. A bathroom with a big enough opening window does not legally need a fan.
What I would say beyond the code: put in both if you can. A fan moves damp air out on a February morning when nobody is opening a window. The window handles the rest of the year and gives you light the fan cannot. Rooms with only one of the two are the rooms where I see mold and mildew on the ceiling.
Your own municipality adopts its own edition of the code and can amend it. The text above is the model code. The permit desk in your town has the final word.
3. The Opening You Already Have
There is no standard size worth memorizing, because replacement units are built to your opening rather than picked off a shelf. What matters is measuring the hole correctly and knowing the one minimum above.
Take four numbers, measured inside the existing jambs rather than off the trim:
- Three widths: near the head, halfway down, and down at the sill. Order to the narrowest reading you get.
- Three heights, taken left, center and right. Again the shortest one is the one that binds.
- Depth from the inside face of the trim through to the outside face of the siding or brick.
- Both diagonals. If they do not match, the opening has shifted and the new unit gets set on shims and squared inside it.
When the old unit comes out, the piece we most often find gone is the sill itself. Water runs down the glass for twenty years, sits in the corner where the trim meets the frame, and the wood underneath goes soft long before anything looks wrong from inside the room. The stool you set things on and the apron beneath it go first, and fresh caulk over the top hides that rather than stopping it. If the flashing above the window has failed as well, water is arriving from outside at the same time. Worth knowing before anyone quotes it, because a rotten sill means carpentry on top of a window.
Bathrooms carry one extra check the other rooms do not. Look at what is in the wall beside the window. A shower valve, a vent stack or a towel bar blocking the swing all change what can go in there. That is worth a photograph before anyone quotes it.
4. The Types That Work in a Bathroom
Six styles turn up in bathrooms. The room usually picks one for you.
The drawings below are illustrations rather than photographs of our own work. Each window is shown part way open on purpose, because closed, all six of these look much the same.
Awning
An awning is hinged along the top, so the bottom swings out. It is the one I fit most often in a bathroom. Set high on the wall it vents steam, holds privacy without any special glass, and stays open in rain because the sash acts as a small roof over the gap.
Casement
Hinged at the side and cranked open like a door. It gives the most airflow of any style, because the whole opening clears. The screen sits on the inside, and the operator is a crank you reach across the sash to turn. Worth checking the swing against the outside: over a walkway or a deck rail, a casement is the wrong pick.
Hopper
A hopper is an awning turned the other way up. The hinges run along the bottom edge, so the head of the sash leans into the room. Common in older St. Louis houses in small, high openings. It vents well, but the sash tips into the room, so keep it clear of a shower curtain.
Slider
A slider has one sash gliding sideways past the other. Nothing projects in or out, which is why it suits a tight room. The trade-off is that only half the width ever opens, so a slider ventilates less than its size suggests.
Double-hung
A double hung has two sashes moving up and down in the same frame. Both tilt in for cleaning, which matters in a room that films up. Open the top sash a few inches and warm damp air leaves without a draft crossing the room.
Picture
A picture window is fixed glass that does not open. It only works where a fan does the ventilating, because a picture window contributes nothing toward the 3 square feet of openable area. Fitted beside an awning it gives you light and airflow together.
5. Privacy Without Losing the Light
Two ways to do it, and they work differently.
Obscure glass. The pattern is in the glass itself, so it never needs cleaning, never falls down and works at night with the light on. That last point is the one people forget. A blind or a film gives you nothing once the room is lit and the outside is dark. ProVia lists seven patterns: Chinchilla, Fluted, Frosted, Gluechip, Obscure Pebble, Taffeta and Waterfall. Four of the seven are not offered on their EcoLite line, so the pattern you like can decide the window line you end up with. Other makers sell much the same thing under their own names, so you will also see reeded, rain glass and acid etched on a showroom board.
Height. A sill set above eye level does the same job with plain glass and costs nothing extra. It is why the awning high on the wall is such a common answer in a bathroom.
Glass block is the third option people raise. It is masonry rather than a window, it does not open, and it is laid by a mason. We do not fit it. If the room already has an exhaust fan and you want obscured light with no moving parts, it is a fair answer, just not one that comes from us.
The honest limit on all of this comes from ProVia rather than from me. Nobody publishes a privacy number for these patterns. ProVia says plainly that how private the glass looks depends on how far you stand from it and on the light inside the room compared with the light outside. So the only reliable way to choose is to hold a sample up. We keep them at the showroom, and the photos on any manufacturer’s website were taken in one particular light.
Tinted glass is a different thing and it is usually the wrong answer here. A tint cuts the light coming in without doing much about the view, which is the opposite of what a bathroom wants.
Frame Material in a Wet Room
Vinyl is the usual answer. It does not rot, does not need painting and does not mind the humidity swing a bathroom puts it through twice a day. Fiberglass is stronger and holds paint, which matters more on a large opening than a small one. Wood looks the part in an older house but wants a maintained finish in exactly the room least suited to one.
The units we fit are ProVia, across their Endure, Aspect and Aeris lines. Platinum dealer with a walk-in showroom, according to ProVia’s own dealer locator. Check it there rather than taking our word for it.
Aluminum is the one to avoid in this room. It conducts heat straight through the frame, so it runs with water in winter. Ask what is in the insulated glass unit as well as what the frame is made of. Ask for the U-factor, the SHGC and the condensation resistance rating on the unit you are actually buying, not the best numbers in the range. In a room making steam twice a day, condensation resistance is the one to read first. A low-E coating and an argon fill between the panes hold the inside face of the glass warmer in January. A warmer inside face is what cuts condensation in a room making steam twice a day.
Condensation on the inside of the glass in winter is not always a fault. It tells you the room is making more moisture than it is clearing. A warmer edge on the sealed unit helps, and so does running the fan for longer after a shower. If it runs between the panes rather than on the face of the glass, the seal has failed and that is a different conversation.
When This Is Not Our Job
- Fixing the window you have. A stuck sash, a failed crank or a single fogged pane is repair work. You do not need a window company for that, and we would be the wrong call. We put in new units and do not rebuild old ones. A glass and repair shop handles it, and the bill is a small share of what a new unit costs.
- Anything commercial. ProVia engineers these units for houses, and houses across St. Louis and St. Charles County are where we stay.
- Moving the opening. Making the hole bigger or shifting it along the wall touches framing and sometimes plumbing. That is a remodel with a window in it, and it wants a remodeler running the job.
Common Questions
Getting a Quote You Can Compare
Make any quote say three things: whether the glass is tempered, which obscure pattern is priced, and whether the figure includes putting the wall back. Two totals without those behind them cannot be compared, and the gap between them is usually one of the three.
The honest limit on all of it: everything above tells you what to ask and what the code will allow. Finished work is in our photo gallery. What none of it can tell you is what your own bathroom will cost. You cannot know that from a web page, because it depends on what is behind the tile, and nobody knows until the old unit comes out.
The way to settle it is to have somebody stand in the room with a tape and tell you which side of those two 60 inch lines your glass falls on. That visit is free and there is nothing to sign at the end of it. Styles, glass and frame options are laid out on our replacement windows page, and every job we do carries a 10 year workmanship guarantee. Call 314-277-5952, or book a free visit and somebody will measure it for you.
