Flush casement vs flush sash windows: Clearing up the terminology
Flush casement vs flush sash windows is one of the most common comparisons homeowners search for, but the answer is straightforward: they are the exact same window. Both terms describe a casement window where the opening sash sits perfectly level with the outer frame when closed, creating a flat exterior profile.
There is no actual product difference, and this guide will explain how the confusion started and why this single style has become the most popular window choice in the UK.
Why the industry uses two names for the same window
The word “casement” refers to any window that opens outward on side hinges, as opposed to a traditional vertical sliding sash window. The word “sash” simply means the moving panel that holds the glass. When that panel sits flush with the frame rather than overlapping it, you get a flush window. Some manufacturers label this “flush casement.” Others call it “flush sash.” Both terms caught on in different regions and among different suppliers, creating the impression of two separate products when there is only one.
This is a constant point of confusion for homeowners, the topic regularly appears on homeowner forums such as Reddit, where contributors consistently clarify that the two terms describe an identical window style.
Before the 1930s, most British homes had timber casement windows with a naturally flush profile. When mass- produced uPVC arrived in the 1980s, manufacturers adopted the “stormproof” lipped design because it was cheaper to seal. When demand for heritage-style windows later returned, the industry reintroduced the flush design under both names, and the confusion stuck.
Why flush windows are so popular right now
Flush windows have moved from a niche conservation requirement to the most requested style across new builds and renovations alike. The appeal comes down to three specific factors.
Planning approval. Local planning officers require replacement windows that replicate the proportions of pre-1932 timber originals in conservation areas and Article 4 properties. Flush windows meet this requirement where stormproof styles do not.
Heritage look without the upkeep. Modern flush windows are manufactured in uPVC with realistic woodgrain foils. Timberlook takes this further with patented Timberweld corner joints that replicate traditional timber butt joints, eliminating the diagonal weld marks that standard uPVC windows show. The result looks like painted timber at street level but will not rot, warp, or need repainting.
Architectural versatility. The flat profile suits Georgian townhouses, Victorian terraces, and contemporary new builds equally well. Browse the Timberlook gallery to see installations across different property types, or explore colour and hardware options to match your home’s character.
Ready to see how flush sash windows could work for your property? Find your nearest Timberlook installer or call 01253 888 222 to discuss your project.
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