Casement Windows Explained: Types, Hardware and Safety

A casement window is a window sash hinged at one side, so that it swings open like a door rather than sliding. It is one of the oldest window types still in everyday use and, in Singapore, one of the most common: a large share of HDB flats and private apartments have aluminium-framed casement windows somewhere in the home.

This guide explains how the type works, how it developed, the main variations and hardware, and the safety obligations that come with it in Singapore, where fallen windows are a recognised public safety issue. It is written from the perspective of an engineer who looks at windows as fixings and loads as much as glass and light.

How a casement window works

The window has two basic parts: a fixed outer frame built into the wall, and an opening sash that carries the glass. The sash is attached to the frame by hinges or friction stays along one vertical edge and closed with a handle and locking mechanism on the opposite edge. Because the whole sash opens, a casement can admit almost its full area as ventilation, which a sliding window cannot.

When closed, the sash presses against compression seals around the frame. This gives casements good airtightness and weather resistance compared with sliding types, particularly when they open outward, because wind pressure pushes the sash harder against its seals.

A brief history

Hinged windows were in use in medieval and Tudor Europe, often as small iron-framed casements filled with leaded panes of glass set into masonry or timber frames. In Britain, the vertically sliding sash became fashionable from the late seventeenth century and dominated Georgian and Victorian housing, but the casement never disappeared from vernacular building and returned strongly with the Arts and Crafts movement. Our sibling article on the sash window traces that rival tradition.

The twentieth century brought steel and then aluminium casements, mass-produced and slender, which suited modernist façades. In tropical Asia, the casement fitted well with the need for maximum ventilation, and aluminium casements became standard in public and private housing.

Types of casement window

Side-hung casement — the standard form, hinged on the left or right.
Top-hung casement — hinged along the top and opening outward at the bottom; sheds rain well and can be left ajar during showers.
Bottom-hung or hopper — hinged at the bottom and tilting inward at the top; often used for high-level ventilation.
French casement — a pair of sashes meeting in the middle with no central mullion, giving a wide clear opening.
Tilt-and-turn — a European type that opens inward either as a side-hung casement or tilts at the top for secure ventilation.
Push-out casement — operated by pushing the handle rather than a crank or stay, common in contemporary designs.

A casement window can be combined with fixed lights, louvres or top-hung panels within the same frame. For an overview of how these sit among other forms, see our hub on types of windows.

Hardware and construction

The weak point of any casement is not the glass but the hardware that holds the sash to the frame. Three components matter most:

Friction stays or hinges — the arms that allow the sash to open and hold it in position. They carry the full weight of the sash when it is open and must resist wind loads.
Rivets and screws — the fixings that attach stays to frame and sash. Their material and condition are critical.
Locking handles — which hold the sash closed against suction on the façade.

On a façade, an open sash is a lever. Its weight and any wind load act at a distance from the stay, and the fixings must take that moment repeatedly over years of opening and closing. Corrosion, wear or loosening of those small components can let a sash drop out entirely. This is why casement maintenance is not cosmetic.

Frame materials include aluminium, uPVC, steel and timber. Aluminium dominates in Singapore for its slender sections and durability, though thermally broken profiles and double glazing are becoming more common in projects concerned with heat gain and noise.

Casement window safety in Singapore

Singapore’s Building and Construction Authority (BCA) treats window safety seriously. According to BCA, corrosion of aluminium rivets is a main cause of fallen casement windows, and since 2004 a retrofitting order has required homeowners to replace all aluminium rivets in casement windows with stainless steel rivets. BCA has stated that failing to do so can attract a fine of up to S$5,000 and/or imprisonment of up to six months, and that if a window falls due to lack of maintenance the owner can be fined up to S$10,000, imprisoned for up to one year, or both.

Window installation or replacement should be carried out by a BCA-approved window contractor. In HDB flats, the HDB renovation guidelines require owners to engage a BCA-approved window contractor listed in HDB’s directory, and a renovation permit is needed for window replacement. Our guide to HDB window replacement covers the process. BCA’s guidance for homeowners includes checking that rivets are stainless steel, keeping stays and hinges clean and lubricated, and ensuring locks engage properly.

Under the Approved Document, a barrier at the lower edge of a window should generally be not less than 900 mm high, a point to check where a low-sill casement opens over a drop. Where a casement window opens into a common corridor or access route, the open sash must not create a headroom or protrusion hazard.

Choosing a casement window

Casements suit rooms that need strong cross-ventilation, openings with a clear outward swing and locations where airtightness matters. They are less suited to openings onto walkways, balconies with limited space, or very large sashes on exposed high-rise façades, where the weight and wind load on the hardware become significant. In those cases a sliding, top-hung or fixed-and-louvre arrangement may be safer.

In our consulting work, the questions we ask about any casement are practical: what is the sash size and weight, what hardware rating has been specified, what are the fixings made of, and how will the window be maintained from inside? A good window is one that is still safe twenty years later.

Frequently asked questions

What is a casement window?

A casement window is a window whose sash is hinged along one side, or occasionally the top or bottom, so that it swings open rather than sliding, allowing almost the full window area to open for ventilation.

Why must casement windows in Singapore use stainless steel rivets?

BCA identified corrosion of aluminium rivets as a main cause of fallen casement windows, and since 2004 a retrofitting order has required homeowners to replace aluminium rivets with stainless steel ones, which resist corrosion and keep the sash securely fixed.

Who can replace casement windows in an HDB flat?

Window replacement in an HDB flat should be carried out by a BCA-approved window contractor listed in HDB’s directory, and a renovation permit is required for the works.

Are casement windows better than sliding windows?

Casement windows open more fully and seal more tightly, which helps ventilation and weather resistance, while sliding windows take no swing space and have fewer projecting parts; the better choice depends on the room, the façade exposure and how the window will be maintained.

How often should casement windows be checked?

BCA encourages homeowners to check their windows regularly, looking for corroded or loose rivets, worn stays and hinges and locks that do not engage, and to have any defects repaired by an approved window contractor promptly.

Concerned about façade or window safety on your building? Talk to our consultancy or get in touch.