Types of Windows: How Each One Opens, Where It Fits and Its Downsides

Most houses use a handful of window types, and the difference between them comes down to how the sash moves. A sash is the glass plus the frame that holds it ². In a double-hung or single-hung window the sash slides up and down; in a slider it moves sideways; a casement swings out on side hinges like a door; an awning hinges at the top and a hopper at the bottom; a picture window does not open at all ^{1 6}. Bay, bow and garden windows are not separate mechanisms but assemblies of several windows that project out from the wall ^{4 5}. Egress describes a job, not a shape: a window big enough to climb out of in an emergency ⁷.

Each type trades something. Windows that slide stay flush with the wall but have more moving parts and more places for air to slip through; windows that swing out seal tightly but need clear space outside; fixed windows are the simplest and most airtight but never let in fresh air ^{1 3 11}. The sections below take each type in turn, with how it opens, where it is usually used and its downsides, and link to the articles that cover cost.

How the main window types compare

Sources for the table: ^{1 2 3 4 5 6 7 8 9 10 11}.

Double-hung windows

A double-hung window has two sashes stacked one above the other, and both move: the bottom slides up and the top slides down ². Opening both at once lets warm air leave at the top while cooler air comes in at the bottom, which Andersen calls circular ventilation ². Many double-hung windows have tilt-in sashes, so both sides of the glass can be cleaned from inside the house, which is why they are common on upper floors ¹. The downside is complexity: both sashes move, so Andersen says there are more parts that may need maintenance over time, and it suggests a single-hung window when a movable top sash is not needed ². The double-hung window cost article covers what they cost.

Single-hung windows

A single-hung window looks like a double-hung from the street, but only the bottom sash moves; the top sash is fixed ². Andersen says the fewer moving parts can help reduce energy loss, and describes a single-hung as giving the look of a double-hung at a more economical price ^{1 2}. The downsides follow from the fixed top: it cannot vent from the top, and Andersen says single-hung windows do not tilt in, so the outside of the glass is cleaned from outdoors ². That matters little on a ground floor and a great deal on a second story. The single-hung vs. double-hung article covers how to tell which one you have.

Casement windows

A casement window is hinged on one side and swings outward like a door, usually with a crank ¹. Because it opens top to bottom it can bring in a lot of air, and the crank makes it easy to open over a kitchen sink or counter ¹. When it closes, the locking hardware pulls the sash into the frame; Andersen calls the casement one of its most energy-efficient window types and says the seal tightens when the wind blows against it ³. The downside is the outward swing: Andersen advises against a casement next to a walkway, porch or deck where the open sash would be in the way ¹. The crank and hinges are also more hardware than a sliding window has. More detail, including cost, is in the casement windows article.

Awning windows

An awning window is hinged at the top and opens outward from the bottom, so the open sash forms a small canopy that keeps rain out ¹. That makes it useful in bathrooms and other rooms that need air in wet weather, and its wide, short shape fits high on a wall or in a basement with little wall above ground ^{1 6}. Andersen groups awning windows with casements among its most efficient windows, citing their design and seal ³. The downside is projection: the open sash sticks out from the wall, so placement next to a path, porch or deck needs the same thought as a casement.

Hopper windows

A hopper window is the reverse of an awning: hinged at the bottom, it tips into the room from the top ⁶. Andersen describes hoppers as small windows commonly used to let air into basements and bathrooms ⁶. The downside is that the open sash leans into the room, where it can get in the way of a counter or shelf. Andersen also says it no longer makes hopper windows ⁶.

Sliding windows

A sliding window, which Andersen calls a gliding window, is like a double-hung window turned on its side: two sashes sit next to each other and one slides along a track ¹⁰. It opens flush with the wall, so it suits spots next to a deck, patio or walkway, and its horizontal shape fits basements and low walls ¹⁰. Andersen says its simpler design, with fewer moving parts and pieces, makes it easier to maintain ¹⁰. The main downside is that in a standard two-sash slider one sash moves and the other is stationary, so only part of the window opens at a time ¹⁰. Which side opens is chosen when the window is ordered, and it is described from the outside, which is easy to get backward ¹⁰.

Picture windows

A picture window is fixed: it does not open ¹¹. Because nothing moves, it can be made larger than an operable window and has fewer paths for air leakage, which Andersen describes as making it the most energy-efficient window type ¹¹. Picture windows are often the large center unit in a combination, with opening windows beside or below them ¹. The downsides are no ventilation, the outside of the glass must be cleaned from outdoors, and a picture window can never serve as an emergency exit ^{6 11}.

Bay windows

A bay window combines at least three windows into one unit that projects out from the wall, usually a picture window in the center with opening windows on each side ⁴. The side windows are set at angles such as 30, 45 or 90 degrees; the 90-degree version is called a box bay ⁴. From the outside a bay has a roof on top and either brackets underneath or wall framing that runs down to the foundation ⁴. The downsides are structural and thermal. A bay is heavy, needs proper support and roofing, and because it projects past the wall it is more exposed; Andersen notes that condensation can form more easily in a bay and suggests asking the installer about extra insulation at the top and under the seat board ^{1 4}. Costs are in the bay and bow window cost article.

Bow windows

A bow window is technically a type of bay, but it curves out gently instead of at sharp angles ⁴. Andersen's bow windows use at least four casement windows set at small angles to one another ⁴. A bow projects less than a bay and takes up less space outside ⁹. The downsides: with more panels it is wider and heavier, which makes installation harder, and bow windows are often sold with few or no panels that open, so they may bring in light without much air ⁹.

Garden windows

A garden window is a small box that projects from the wall with glass on all sides, including the top, so it works like a miniature greenhouse; it is most often found over a kitchen sink ⁵. The downside is that glass roof. Andersen says garden windows have a reputation for leaking water through the top, and that it does not make a garden window with a glass top for that reason; it suggests a box bay with a solid roof as the replacement ⁵.

Egress windows

An egress window is any window large enough to serve as an emergency escape and rescue opening. Under the 2021 International Residential Code, Section R310, basements, habitable attics and every sleeping room must have at least one such opening; the clear opening must be at least 5.7 square feet (5 square feet at grade level), at least 24 inches high and 20 inches wide, with the bottom no more than 44 inches above the floor, and it must open from inside without keys, tools or special knowledge ⁷. Your city or county adopts its own edition of the code and may amend it, so the local building department has the final word. Andersen notes that casement and gliding windows can be sized to meet egress requirements, and that a picture window will not work as one ⁶. The downside is the work around it: a basement egress window below ground needs an area well, which R310.4 also regulates ⁷.

Storm windows

A storm window is not a replacement window but a second panel added to an existing one: exterior storms go on the outside of the primary window and interior storms on the inside ⁸. ENERGY STAR describes low-e storm windows as an option where full replacement may be difficult, such as historic homes ⁸. The downsides: ENERGY STAR says storm windows work best over primary windows in good condition and may not be appropriate over rotted or damaged ones, and over metal-framed windows they need thermal breaks to avoid conducting heat and cold through the frame ⁸.

How to choose among them

Start with what each opening has to do. If a window has to vent a room where you reach over a counter, a crank-operated casement or awning is easier to open than a hung window ^{1 10}. Next to a walkway or deck, a window that opens flush with the wall, such as a hung window or a slider, stays out of the way ¹. A bedroom or basement bedroom needs an opening that meets the egress size in the code your area has adopted, which in the model code is IRC Section R310 ⁷. Where the window only has to bring in light or frame a view, a picture window does it with the fewest moving parts ¹¹.

Style matters too. Andersen pairs single- and double-hung windows with traditional homes and casements, sliders and picture windows with contemporary ones, though most houses mix several types ¹. Frame material is a separate choice from window type, covered in window frame materials compared, and the glass package is covered in energy-efficient windows explained.

When you ask installers for prices, name the type, size and opening direction for each window so the quotes line up. The window replacement cost guide explains what drives the price, and how to choose a window installer covers what a written quote should list. When you are ready, you can compare quotes from window installers.

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About these figures

• ¹ Reported: Andersen's descriptions of how double-hung, single-hung, casement, picture, bay, sliding and awning windows open, where they fit and its placement advice, checked October 22, 2026.
• ² Reported: Andersen's definitions of single-hung and double-hung windows, tilt-wash and maintenance notes, checked October 22, 2026.
• ³ Reported: Andersen's description of how casement and awning windows seal and their efficiency, checked October 22, 2026.
• ⁴ Reported: Andersen's description of bay and bow windows, flanking angles, support and insulation, checked October 22, 2026.
• ⁵ Reported: Andersen's description of garden windows and the leaking-roof issue, checked October 22, 2026.
• ⁶ Reported: Andersen's descriptions of hopper and basement windows and which types can meet egress size, checked October 22, 2026.
• ⁷ Official record: International Residential Code 2021, Section R310, minimum egress opening area, dimensions, sill height and area wells, checked October 22, 2026.
• ⁸ Official record: ENERGY STAR description of interior and exterior storm windows and when they work best, checked October 22, 2026.
• ⁹ Reported: Angi's comparison of bow and bay windows (projection, weight, ventilation), updated August 4, 2026, checked October 22, 2026.
• ¹⁰ Reported: Andersen's description of sliding (gliding) windows and active and stationary sashes, checked October 22, 2026.
• ¹¹ Reported: Andersen's description of picture windows, efficiency and cleaning, checked October 22, 2026.