WINDOW TYPES

Window Styles Explained: Which Type Fits Which Opening

A style is a decision about an opening, not a preference from a catalog. Work out what each opening has to do — move air, let a person out, hold a view, clear a walkway — and the shortlist usually writes itself.

How replacement windows differ →

A bright living room corner with a large picture window and a casement window

What decides a style
The obligations of the hole: whether it has to let a person out, whether it can be reached, what has to fit past it outside, and how much air the room depends on it for.
What it does not decide
Frame material and glass package are separate choices, and nearly every style is made in nearly every material. Read frame materials and energy ratings separately.
Cost drivers
Glass area, how much hardware moves, and — much the largest — whether the wall is altered. No survey this site can cite breaks its figures down by style; the published national ranges are on the cost guide.

What types of windows are there?

Five styles cover the overwhelming majority of US replacement work. Each has its own page here.

Those five differ in one respect that matters more than any other: how the sash moves, or whether it moves at all. A sash that slides in its own plane, a sash that swings out on hinges and a pane that never moves seal differently, cost different money to build, take different hardware and fail in different ways twenty winters later. Everything else — grille patterns, exterior color, glass coatings — sits on top of that one mechanical decision and can be changed without changing it.

The five styles, across one table

Mechanism first, because everything a homeowner notices later follows from it.

Compared on	Double-hung	Casement	Sliding	Picture	Bay and bow
How the sash moves	Vertically, in two tracks	Swings out on side hinges	Horizontally, on rollers	It does not move	Flankers open; the center is usually fixed
Share of the opening that opens	About half the height	Close to all of it	About half the width	None	Only the flanking units
Space it needs to operate	None either side	A clear arc outside	None either side	None	A clear arc at each flanker
Where the screen sits	Outside	Inside the room	Outside, on its own track	There is none	Outside, on the flankers
The opening it suits	Taller than it is wide	Tall and narrow, or hard to reach across	Wider than it is tall	Any hole whose job is the view	A wall you intend to push out past
Does the wall change?	No	No	No	No	Usually — see the projecting-assembly page

Mechanism and fit, not a ranking. Air leakage, U-factor and solar heat gain are certified per unit rather than per style, and belong on the label of the window you are actually buying.

Awning and hopper windows

An awning is hinged at the top and cranks outward from the bottom, so the open sash forms a small shelf over the opening.
That shelf is the point. It can stay open in light rain without water running down the inside of the glass, which is why awnings appear high on bathroom walls and over kitchen sinks.
A hopper is the same idea inverted: hinged at the bottom, tilting inward at the top, low in a basement wall where nothing may project into a window well.
Both use crank hardware and a compression seal, so they behave more like a casement than like anything that slides.
Name them by style to a contractor. The little one over the sink is how the wrong unit arrives on the truck.
Neither has a page here. The search demand behind them in this market does not justify one, and publishing a thin page to cover a word is how a site stops being useful. The operating principles above are what to take into the conversation.

Combination units

Most large openings are assemblies. A fixed center pane flanked by two operable units, joined at the factory or on site.
It buys both things at once — the glass area of a fixed pane and sashes that still deliver air.
Every joint is a seal that has to be made correctly, and the assembly is heavier and more awkward to set.
Three units show less glass than one sheet of the same width, because the members between them are opaque.
Ask how many units are in a line item. That question separates companies that measured your house from companies that priced a category.

Start with the opening

Five things about a hole in a wall decide the style, and none of them is taste.

Every opening in a house carries a short list of obligations. Some are legal: a bedroom opening may have to let a person out and a firefighter in. Some are physical: a window over a kitchen counter has to be reachable across the counter, and a window beside a garden path cannot swing into somebody walking past. Some are about comfort: a room with one window depends on that window for its air, while a room with three can afford one of them to be fixed glass.

Work through the openings in that order — obligation, reach, clearance, air, view — and most rooms in a house will resolve to one or two candidate styles before anybody shows you a sample. That is a much stronger position to be in at the measurement visit than choosing from a folder, because a salesperson who is asked for a style has to explain why, and a salesperson who is handed a style has only to price it.

It also protects you from a quiet substitution. Replacing an operable window with a fixed one is cheaper to build and looks handsome in a rendering, but it removes ventilation from that room permanently, and on a sleeping room it may remove something the code required. Knowing which of your openings can accept that change, and which cannot, is the single most useful thing to bring to a first appointment.

Which window type is best for ventilation?

The honest answer is about geometry: how much of the opening actually opens, and which way the moving sash faces.

A hinged sash that cranks outward exposes close to the whole opening when it is wound out, and because it swings it can also catch air that is moving along the face of the wall rather than straight at it. A sash that slides — vertically in a hung window, horizontally in a slider — can only ever uncover part of its opening, because the moving half has to go somewhere and the only place it can go is in front of the other half. A fixed pane uncovers none of it.

That ranking is a starting point rather than a verdict, because ventilation in a house is about pairs of openings and not single ones. Air moves through a room when it has somewhere to leave, so a room with two modest openings on different walls will out-ventilate a room with one large one. Before you pay for the style with the largest opening area, look at where the second opening in that room is, and whether the prevailing summer wind reaches the wall you are about to spend the money on.

Which windows meet egress requirements?

Any style can, and no style always does. The unit has to be sized and specified for it.

Building codes in the United States require an emergency escape and rescue opening in sleeping rooms and in habitable basements. What satisfies that requirement is not a style name, it is a measured clear opening: the hole that remains once the frame, the sash and the hardware are all in place and the window is fully open. That number is always smaller than the rough opening in the wall, and by different amounts in different styles, which is why a like-for-like replacement can quietly fail a requirement the original window passed.

This site does not publish escape-opening dimensions. Those dimensions come from the model code edition your jurisdiction has actually adopted, adoption varies by state and by edition, and a number carried over from another state is worse than no number. What to do instead is concrete: ask each company to state the clear opening of the unit it is quoting for any sleeping room, get it in writing, and check it against your local building department before you sign. A contractor who cannot produce that figure for a bedroom window has not finished the quote.

Which window type is cheapest?

Price tracks hardware count, glass area and whether the opening survives the job.

Three things drive the price of one unit before anybody negotiates. The first is how much glass it holds, because glass is sold by area and a large sheet of insulated glass also needs a stronger frame to carry it. The second is how much hardware moves: balances, hinges, cranks, locks and weatherstripping all cost money and all have to be installed and adjusted. The third, and the largest by far, is whether the wall is altered — a unit that drops into the existing opening is a different job from one that requires the opening to be cut, framed and finished.

We do not publish a price ranking by style, and the reason is worth stating plainly: the cost figures this site is able to cite are national survey averages published by third parties, and those surveys do not break their numbers down by window style. Inventing that breakdown would be easy and it would be fiction.

What you can do with the three drivers is read your own quotes against them. Ask which line items change if an opening keeps its existing frame rather than being taken back to the structure, and ask what the same opening would cost with one fewer moving sash in it. Two companies quoting the same house will frequently have made different assumptions about both, and those assumptions are worth more than any published average.

What is the difference between a bay and a bow window?

Both project out past the plane of the wall, and both are assemblies of several units rather than one window. A bay is angular: a wide center unit with two flanking units set back at an angle, usually a distinct corner where they meet. A bow is curved: four or more equal units set at shallower angles so the run reads as an arc rather than a shape with corners. For a homeowner the consequential part is not the shape. It is that either one is a structure that hangs off the side of a house, carries its own small roof and needs support, which puts it in a different category of work from any of the flat-wall styles on this page. The projecting-assembly page covers what that means for the quote.

Questions about style, for the measurement visit

Six that a company which has measured your house can answer on the spot.

Which style are you quoting for each opening, and did you choose it or did I?
What is the clear opening of that unit once the frame and hardware are in place?
Does the style you propose keep the existing frame, or does the opening have to be altered?
If you are proposing a different style from what is there now, what changes on the inside trim?
Which of these openings, if any, is in a sleeping room?
Does the screen sit inside or outside on the styles you are quoting?

Know the style before the folder comes out

Read what an estimate should itemize, then decide which companies to ask.