Aluminium Casement Windows: A Homeowner's Guide
Updated: 12 hours ago
Aluminium casement windows are windows whose opening sash is hinged at the side or the top and swings outward, held in a slim, thermally broken aluminium frame. They are the most common window type in British homes for a good reason: they seal tightly, they open wide for ventilation, and in aluminium they can be made with the slimmest frames of any material. This post covers the two casement styles, what goes into a good one, and how to specify yours.
What is an aluminium casement window?
A casement is any window where the opening part is hinged rather than sliding. Side-hung casements open like a door; top-hung casements open outward from the bottom and are often used as vents above a fixed pane. The profile includes a thermal break, an insulating strip between the cold outer face and the warm inner face. Our aluminium windows and doors are made to measure in casement, tilt-and-turn and fixed styles.
How a casement compares:
Casement: opens outward; the most versatile and usually the least expensive opening style.
Tilt and turn: opens inward, tilts for secure ventilation, cleans from inside; best on upper floors.
Sash: slides vertically; the right look for many Georgian and Victorian fronts, at a higher price.
Flush casement or stormproof casement?
This is the first design decision and it changes the look of the whole elevation.
A stormproof casement has a sash that overlaps the outer frame, so the sash sits slightly proud of the frame face. It is the traditional modern casement, very weathertight, and the overlap hides the gap. From outside you see a stepped profile.
A flush casement has a sash that closes level with the frame, so the whole window reads as one flat plane. It is the older, pre-war look, and it is the style conservation officers usually prefer on period houses. Aluminium flush casement windows have become popular on contemporary homes too because the flat face suits clean modern elevations. Flush casements rely on high-quality gaskets rather than an overlap to keep the weather out. A well-made one, with multi-point locking that pulls the sash tight to the frame, is fully weathertight; the stormproof overlap was originally a way of compensating for poorer seals.
We supply both. Flush is the better match for a period or minimalist house; stormproof is the better match where the existing windows are stormproof and only some are being replaced.
Why aluminium rather than timber or standard frames?
Aluminium is strong for its weight, so the frame stays slim around a large pane. It does not swell, shrink or rot, and the powder coat never needs repainting. Early aluminium windows had no thermal break and ran cold; in England a replacement window now needs a whole-window U-value of 1.4 W/m²K or better, which a thermally broken casement with modern double glazing is designed to meet, and triple glazing takes it lower.
What sizes and configurations are possible?
Aluminium casements can be made large, with the practical limit set by the glass weight the hinges can carry, which varies by system; ask for the maximum sash size in writing. Beyond that, the window is split into a fixed pane with an opening casement beside it, or a pair of casements meeting at a central mullion, or a run of fixed lights with top-hung vents above.
Common arrangements are a fixed central light with side-hung casements either side, a tall narrow casement for a stairwell, and a top-hung vent over a fixed pane.
What glazing should a casement have?
Low-emissivity, argon-filled double glazing is standard. Triple glazing improves insulation and sound reduction but is heavier, so hinges and sash size are specified to suit. Solar-control glass suits south and west elevations.
Safety glass, either toughened or laminated, is required by Building Regulations in any pane within 800mm of the floor and in any glazing near a door. Laminated glass also adds security because it holds together when broken.
Hardware, security and finish
Multi-point locking is standard on every casement we install: turning the handle throws several locking points along the sash into keeps in the frame, so the sash is held on all sides rather than at one latch. Concealed, low-profile hardware keeps the inside face clean, and friction hinges hold the sash open at any angle without a stay. Restrictors can be fitted where a window is above ground floor. For security, ask for windows tested to PAS 24; Secured by Design, the police-backed scheme, builds on it.
Finish is a wide range of RAL colours, applied as a powder coat and available in dual colour, one colour outside and another inside, so a black or anthracite exterior can pair with a white interior. The same colours run across our doors, so windows and doors match through the house.
How much do aluminium casement windows cost?
A slim-frame aluminium casement costs more than an off-the-shelf window, with size, configuration, triple glazing and colour moving the figure. Our guide to aluminium windows cost explains what drives the price.
Aluminium casement windows questions, answered
Do aluminium casement windows get condensation?
Not on the frame, if the frame is thermally broken. Condensation on old aluminium windows came from unbroken frames that ran cold. On a modern frame the inner face stays near room temperature, so moisture does not form on it.
Can a casement window open inward?
A casement opens outward. If you want a window that opens inward, for cleaning or because of an obstruction outside, a tilt-and-turn window is the answer, and we make those in the same slim aluminium.
How long do aluminium casement windows last?
The frame and powder coat are expected to last decades without repainting. Sealed glazing units are typically the first component to need replacement, after twenty years or so, and they can be replaced within the same frame.
Talk to our design team
If you are replacing windows across a house, casements will do most of the work. We are glad to look at your elevations and set out flush and stormproof options side by side.
