A casement window is hinged at the side or the top and opens outward. It is the most common window in the UK, and in aluminium it is the cheapest route into a slim-frame window — typically £520–£1,050 supplied and fitted, depending on size.
The casement is where the frame-thickness argument matters most, because a casement window has a frame and an opening sash — two thicknesses of material stacked on top of each other around every opener. In uPVC that combined section is often 100mm or more of solid white plastic. In aluminium it can be under 70mm.
The visual difference on a bay-fronted 1930s semi is dramatic: the same aperture, noticeably more glass, and a much finer line between the panes.
55–65mm thermally broken frame; double glazed 4-16-4 with a low-E soft coat, warm-edge spacer and argon fill; whole-window U-value around 1.3 W/m²K; polyester powder coat in RAL 7016 anthracite; internally beaded with multi-point locking; trickle vents where the room does not already have background ventilation.
| Job | Typical cost |
|---|---|
| Casement window, approx. 600 × 900mm supplied & fitted | £520 – £760 |
| Casement window, approx. 1200 × 1200mm supplied & fitted | £700 – £1,050 |
| Casement window, approx. 1800 × 1200mm supplied & fitted | £980 – £1,450 |
Ranges include VAT and installation. Final price depends on size, spec, access and site condition — a survey gives you a fixed number.
As a supplied-and-fitted guide: around £520–£760 for a small window (roughly 600 × 900mm), £700–£1,050 for a standard 1200 × 1200mm, and £980–£1,450 for a large 1800 × 1200mm. Colour, glazing spec and access all move the number.
Yes — with a flat-faced heritage profile, an external putty-line bead and slim glazing bars, an aluminium casement will read as a steel window from the street. Most conservation officers accept it where a chunky uPVC profile would be refused.
Outward, in almost every UK installation. If you need an inward-opening window — typically for a flat, a balcony or somewhere you can't reach the outside face to clean — specify tilt & turn instead.
A modern aluminium casement uses multi-point locking with internal beading, so the glass cannot be removed from outside. Specify PAS 24 hardware and laminated glass on ground-floor and accessible openings.
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