Skip to content
Price Your WindowsGet your estimateMy estimates

Window & door types

All window types

Bay window

Three angled panels project outward from the wall: typically a fixed center picture unit flanked by two operable side windows.

Bay window

Drag or press ← → to rotate; Home resets the view

Pick a window or door type, drag or use ← / → to rotate the 3D model, and press the mechanism buttons to see how it opens.

How it opens and how it is built

A bay window is a set of windows joined into one unit that stands out from the wall: a wide center window parallel to the wall and two side windows set at an angle to it. Usually the center does not open and the two side windows do, as casements or hung windows.

Because it stands out, the unit needs its own structure: a seat or base under it, a small roof or a cap above it, and support to carry its weight, all sealed and insulated where they meet the wall. In the 3D model above you can check how the side windows open.

Why you'd want it

A bay window brings light in from three directions, widens the view and adds a little floor space inside: a nook or a window seat. It is chosen for a living or dining room where the window is a feature of the room.

A bow window is its curved cousin, with four or five panels and more glass. A large picture window gives much of the light without projecting, and a casement is what usually opens on its sides.

Pros and cons

Pros

  • Light comes in from three directions, and the view is much wider than from a flat window.
  • It adds a nook or a window seat inside without moving the wall.
  • The opening side windows let air in from two directions.

Cons

  • It usually costs more than an ordinary window: the frame, the base, the roof and the support are extra work.
  • It has more joints with the wall, so a poor installation leads to leaks and heat loss.
  • Replacing it is a building job, not a simple window swap, and the base must be insulated.

It's for you if…

  • You want a window seat or a reading nook in a living room or a bedroom.
  • The room is dark and a flat window does not bring in enough light.
  • You are replacing an existing bay window and want to keep the shape of the house.

Don't overpay if…

  • You only want more light: a larger picture window in the wall gives much of it and usually costs less.
  • The wall cannot carry a projecting unit without new support: check the cost of the structure first.
  • You want a smooth curved look across a wide wall: a bow window is the type made for that.

How it affects the price

A bay window usually costs more than an ordinary window of the same width: it is several windows joined into one unit, and it needs a base, a roof or a cap, support and insulation where it meets the wall. It is usually less expensive than a bow window of the same width, which has more panels.

Within the type the width, the angle of the sides, the type of the side windows, the frame material and the roof finish move the price.

All window types and their impact on the price →

Lifespan and care

Each season, look at the roof or the cap above the bay and the sealant where the unit meets the wall, and renew the sealant where it cracks. Once or twice a year care for the side windows as for their own type: clean and lubricate the hardware and check the weatherstripping. Watch the seat inside for damp or cold spots, which point to a leak or a gap in the insulation of the base.

Figures with sources

What a bay window is
a combination assembly which is composed of three or more individual windows either joined side by side or installed within opaque assemblies and which projects away from the wall on which it is installedSource:Glossary: Bay Window — Energy Code Ace, Reference Ace 2013 (California Building Energy Efficiency Standards)
Common angles of the side windows
Common angles are 30° and 45°, although other angles may be employedSource:Glossary: Bay Window — Energy Code Ace, Reference Ace 2013 (California Building Energy Efficiency Standards)
How ENERGY STAR sets its criteria for windows
Performance criteria for windows and skylights are based on ratings certified by the National Fenestration Rating Council (NFRC), and vary for each of the climate zonesSource:ENERGY STAR Key Product Criteria: Residential Windows, Doors and Skylights (U.S. EPA)

What it pairs with

A bay window is mostly glass facing three ways, so the glass unit and its Low-E coating decide much of how warm the nook is in winter and in summer sun. The installation matters more than for a flat window: the base, the roof and the joints with the wall must be supported, sealed and insulated. The frame material and the hardware of the side windows are chosen as for their own type.

How projecting windows are installed →Which glass unit to choose →

Compared with similar types

Frequently asked questions

Does a bay window need a base and support?

Yes. It stands out from the wall, so it needs a seat or base under it, support to carry its weight and a roof or a cap above it. How it is supported depends on the wall and the size, and the installer works it out.

How is a bay window different from a bow window?

A bay usually has three panels: a wide center and two angled sides. A bow has four or five panels that make a smooth curve, with more glass, and it usually costs more.

Is a bay window colder than an ordinary one?

It can be, because it has more glass and more joints with the wall. With a good glass unit and an insulated base and roof it can be comfortable; the quality of the installation decides a lot.

Does the whole bay have to be replaced at once?

It depends on how it is built. Sometimes the windows can be replaced in the existing structure; if the base or the roof is damaged, the whole unit is usually rebuilt. The installer decides after looking at it.

Price it for my home