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A flush casement closes into a rebate. Sash face and frame occupy one plane. A lipped casement overlaps the frame and casts a shadow. That geometric difference governs elevation, sealing and tolerance — and explains why flush casements are specified in conservation areas, period refurbishment and contemporary work. Kanod manufactures aluminium casement systems with flush-surface detailing.

Custom Flush Casement Windows: Sizes, Colours & Design

Performance of Custom Flush Casement Windows

On a terrace, the level elevation is what people notice. On one window, nobody does.

The sash presses against compression seals all the way round. Air leakage figures tend to reflect that, and acoustic performance usually comes out ahead of a lipped casement in the same opening. The difficulty starts when the opening is not square. There is no overlap to absorb a frame that has been installed with a twist, so compression varies around the perimeter and the corners are where it shows. Flush windows have a reputation for being fussy partly because of this — it is a fitting and tolerance issue rather than a design one, but the two get confused. Triple glazing compounds it: the sash is considerably heavier, and the hinges and locking points carry that load in the closed position for years. Kanod’s aluminium casement platforms are built around this closing geometry from the start rather than adapting a standard profile.

Custom Flush Casement Windows: Sizes, Colours & Design

Application Scenarios

Flush casements put back the flat façade that predates stormproof profiles. On a listed building this is usually what the conservation officer wants to see. Cottages and rural properties tend to want the same, and slim glazing bars help.

In renovation work the flush face sits back into the wall. Panes get larger, sightlines thinner, and there is no step at the opening. Kitchen extensions and garden rooms are where this gets noticed. On upper floors, side-hung and top-hung sashes are typically combined with fixed lights so that the line continues across the full elevation.

Custom Flush Casement Windows: Sizes, Colours & Design

Comparison Guide: Flush and Standard Casements

A standard lipped casement overlaps the frame. That overlap sheds water and has been the default for most of the last century. Flush casements remove it; the seal and the joint do the rest.

Flush profiles are machined to tighter tolerance than standard casements. Production runs more slowly and the unit price is higher. Stock levels are also lower, so lead times extend and replacement parts may not be readily available. Whether the premium makes sense depends on position. A front elevation in a conservation area that will be assessed is one thing; a rear window facing a car park is another.

No standard size table applies to flush casements. Opening direction, glass weight, hardware and the structural opening each constrain the feasible range, which is why most projects are specified window by window. For bespoke flush casement windows that is the normal method of working rather than a special arrangement.

Custom Flush Casement Windows: Sizes, Colours & Design

Specification Advice for Bespoke Flush Casement Windows

Determining Flush Casement Window Sizes

Side-hung sashes generally provide the widest clear opening, the relevant dimension for escape windows. The size limit depends on hinge rating and sash weight. Top-hung sashes ventilate without projecting into the room, which makes them suitable where the window opens over a worktop or a path.

Matching Profile and Rebate to the Building

On old buildings, rebate depth and frame profile read from a metre away. A frame in proportion, with glazing bars, drops into a traditional opening as if it belongs; a slim modern profile forced in without adjustment shows at close range. New-build works the other way round — sightlines and glass-to-frame ratio come first, and a narrow profile is fine until drainage or sealing gets squeezed to achieve it.

Selecting Colour and Finish

RAL Classic, NCS and heritage matches are all on the table. Interior and exterior schemes that diverge can be handled with dual-colour finishes. Powder coating holds up on exposed elevations, though no finish is immune to a south-facing wall over twenty years. Where a conservation project needs a heritage colour, matching is usually possible — but check it against a physical sample in daylight. A hex code on a screen tells you almost nothing about how a powder coat will read on the building.

Confirming Compliance and Documentation

Replacement windows sit under building regulations, and in conservation areas or listed buildings, planning as well. The two run on separate tracks and can trip each other up: a scheme that passes building control can still fail planning, and the fix is rarely cheap once frames are ordered. Check both first. Modern flush systems take double or triple glazing and security hardware without changing the external profile, and CE marking applies according to the project.

For projects requiring a level façade with project-specific sizing, Kanod’s casement range is the starting point. Review the Kashang Series aluminium double casement windows for a flush-surface platform, or the New Kelon thermal insulation casement range where thermal separation matters more.