Side-hinged, crank-operated — the tightest seal and the fullest opening
A casement window is side-hinged and swings outward, operated by a crank rather than being slid or lifted. That one difference in how it opens drives everything else about it — and it is why casements consistently outperform other operable styles on air-tightness, ventilation and view.
They are sometimes described as the operable picture window. A casement has no meeting rail dividing the glass, so it gives close to the uninterrupted view of a fixed pane while still opening — and opening completely, not halfway.
This page covers how casements work, the four benefits that usually decide the choice, honest comparisons against the alternatives, the options worth specifying, and the one practical limitation that rules them out on certain openings.
Hinges run the full height of one side of the sash. A crank at the base of the frame drives a gearbox that pushes the sash outward, and reversing it pulls the sash back and draws it tight against the frame.
Fold-down cranks are now standard on most premium lines. The handle folds flat against the frame when not in use, which matters more than it sounds — a fixed crank handle fouls blinds, shades and curtains, and on a window behind a treatment it becomes genuinely awkward.
Push-out casements remove the crank entirely. The sash is unlocked and pushed open by hand, held by friction hinges. It is a more traditional arrangement, offered on some premium lines including parts of Marvin's range, and it suits period work where a visible crank would look wrong. The trade-off is that you have to be able to reach the window to operate it, which rules it out above a counter or a deep sill.
This is the single strongest argument for a casement, and it comes down to a mechanical difference.
When you crank a casement shut and throw the lock, the multipoint hardware pulls the sash against the frame on all four sides simultaneously, compressing the weatherstripping. It is the same principle as the seal on a refrigerator door: the closing action is perpendicular to the seal, so the gasket is squeezed rather than rubbed.
A double-hung or sliding window cannot do this. Their sashes move parallel to the seal, so the weatherstripping works by friction — it has to be loose enough to slide and tight enough to seal, which is a compromise. Over years of operation that friction wears the material, and the meeting rail where the two sashes overlap is a permanent weak point.
The practical result is lower air infiltration and better U-factors from a casement than from a comparable hung or sliding unit in the same product line and the same glass. If the priority is energy performance from an operable window, this is the style to specify.
It also means the hardware is doing real work. A casement whose multipoint lock is out of adjustment does not seal properly, and that shows up as draughts. Worth knowing when diagnosing an older casement that has started to feel cold — see casement operators and casement hinges.
A double-hung or slider can only ever open half its area, because the moving sash parks in front of the fixed one. A casement clears the entire opening.
There is a second effect that is easy to miss. Because the sash swings outward, it projects into the airstream and acts as a scoop — catching a breeze running parallel to the wall and turning it into the room. On a house where the prevailing wind runs along the facade rather than at it, that is the difference between a window that ventilates and one that does not.
The direction the sash swings is therefore a specification decision, not a detail to leave to the supplier. Hinging a pair of casements so both scoop from the same side, or so one scoops in and one exhausts, changes how a room ventilates. Tell us which way the wind runs and we will hang them accordingly.
With no meeting rail, a casement gives an uninterrupted pane. Against a double-hung of the same size you gain both the visual clean line and a measurable amount of glass area, since there is no check rail eating into the middle of the view.
This is why casements pair so naturally with fixed picture windows in a window wall — the sightlines match, and from outside an observer cannot easily tell which units open.
The full clear opening also helps with egress. Bedrooms generally require an operable window meeting minimum clear opening dimensions for escape and rescue. Because a casement opens its entire area, it can often satisfy egress in a smaller rough opening than a double-hung would need — useful when the opening size is fixed by the existing masonry, as it usually is in New York replacement work. Egress hinges that let the sash swing further clear are available where the numbers are tight.
Casements are inherently harder to defeat than hung or sliding windows.
The multipoint lock engages several points around the sash perimeter from a single handle, physically drawing the sash into the frame. Forcing it means defeating every point at once rather than a single central latch.
The hardware is entirely interior. There is no exterior sash to lift, no accessible latch, and nothing to lever from outside. Compare that with a slider, where the sash can sometimes be jacked out of its track.
For openings at ground level or reachable from a fire escape — a common condition in the boroughs — a casement with laminated glass is a genuinely secure assembly rather than a token one.
Every style has a job it does best. The table summarises where each wins.
| Casement | Double-Hung | Slider | Awning | |
|---|---|---|---|---|
| Seal type | Compression — airtight | Friction | Friction | Compression |
| Opening area | 100% of the opening | 50% | 50% | Partial, limited throw |
| Meeting rail | None | Horizontal, centre | Vertical, centre | None |
| Exterior clearance | Required | None | None | Required |
| Open in rain? | No | Partly | Partly | Yes — its niche |
| Cleaning | From outside, or reach through | Tilt-in from inside | Lift-out sashes | From outside |
Against double-hung. Casement wins on seal, ventilation, view and modern appearance. Double-hung wins on traditional and historic fidelity, on tilt-in cleaning from inside, and on convective venting — opening top and bottom lets warm air out the top while cool air enters below, which a casement cannot replicate. In a landmark district, the double-hung may also be the only style that will be approved.
Against awning. These are close relatives, hinged at the top instead of the side, and usually built in the same product families. The awning's advantage is specific and real: because the sash hinges at the top and opens from the bottom, it shelters its own opening and can stay open in light rain. A casement cannot. Casements go larger and scoop more air. The two are often combined — a large casement with an awning above or below it — giving both the view and the ability to leave something open in weather.
Against sliders. Casement wins clearly on seal and ventilation. The slider's advantage is that it needs no exterior clearance at all, which decides it in some locations regardless of performance.
Against picture windows. A fixed unit will always test slightly better on air infiltration and often on U-factor, because it has no operating hardware and no seal that has to open. It is also cheaper, having no operator, no hinges and no lock. But it does not ventilate. The usual answer on a large elevation is to combine them — fixed units for the view, casements at the ends for air.
Casements swing outward, and that swing has to go somewhere. This is the practical constraint that rules them out on certain openings, and it deserves stating plainly before anyone specifies a houseful of them.
The sash needs clear space outside for its full arc. Problems arise over a deck or patio where an open sash blocks a walkway, at a narrow side alley or lot line where the sash would cross the boundary, near a fire escape or egress path where an open window obstructs the route, and over a public sidewalk where a projecting sash at head height is both a hazard and generally not permitted.
In New York the lot-line and alley condition comes up constantly, and it is worth checking at survey rather than discovering at installation. Where clearance is the problem, a slider or a hung window is the answer, or a tilt-and-turn if the budget allows — tilt-and-turn windows open inward and give a compression seal with no exterior swing at all, which is why they dominate in dense European cities for exactly this reason.
The other consequence of opening outward is cleaning: the exterior face is washed from outside, or by reaching through the opening on smaller units. Wash-mode hinges that let the sash stand clear of the frame make that easier on upper floors and are worth asking for.
Glass is where most of the performance sits. Low-E coatings tuned to the elevation, argon fill as standard, laminated glass where noise or security matters, and tempered where code requires it near floors, doors or wet areas.
Hardware options include fold-down cranks, hinge types that trade cost against egress and cleaning access, limit stops where a full swing is undesirable, and finishes to match the rest of the house.
Screens fit on the interior of a casement, since the sash swings out. That is worth knowing because it changes the view slightly from inside — you are looking through mesh whenever the screen is fitted, unlike a double-hung where the screen covers only the open half.
Grilles can be specified between the glass, as simulated divided light with applied bars and a spacer, or as removable interior grilles. In a historic district, check what the designation will accept before choosing.
We carry casements across the full range, and which one suits depends on the project rather than on brand preference.
Andersen across the 100 through E-Series lines, Marvin including push-out options, Pella from Encompass through Reserve, and Alside at the value end. European systems from Cortizo and Reynaers also produce casements, typically with narrower sightlines than American lines.
Tell us the openings, which way the wind runs, whether there is clearance outside, and what the budget is. We will tell you which line fits — and if a casement is the wrong style for a particular opening, we will say so rather than sell you one that will not open properly.
Double-Hung Windows Tilt-and-Turn Windows Sliding Windows Fixed Windows Casement Operators Casement Hinges
Tell us about the opening and we will specify it for you.
