Flush Sash Windows Explained

A flush sash window is a casement where the opening sash sits flush within the frame when closed, rather than protruding over it. The result is a clean, flat, traditional appearance that echoes old timber joinery — with all the benefits of modern materials.

Why they look so good

The flush line is characteristic of historic windows, so flush-sash designs sit beautifully on period and heritage homes, cottages and barn conversions — and they bring a refined, understated look to contemporary properties too.

Materials and performance

Available in uPVC, timber and aluminium, flush-sash windows achieve the same warm U-values (well within the 1.4 W/m²K (WER Band B) requirement) and secure locking as any modern casement. uPVC flush sashes give the look with the lowest maintenance.

Flush sash vs standard casement

Standard casements have the sash sitting slightly proud of the frame. Flush sashes cost a little more but reward you with a noticeably more authentic, elegant finish — especially in heritage colours with period furniture.

Get free quotes and ask local installers to price a flush-sash option alongside a standard casement so you can compare.

Frequently asked questions

Are flush sash windows more expensive?

Usually a modest premium over a standard casement, for a more authentic flush appearance.

Do flush sash windows suit modern homes?

Yes — the clean, flat lines look crisp and contemporary as well as traditional.