Flush Sash Windows Explained

Flush sash windows are casement windows where the opening part, the sash, closes into the frame so it sits level with it, instead of lapping over the front as a standard uPVC casement does. The result looks like a traditional timber window, with the low upkeep of uPVC. Cristal Windows supplies and installs uPVC flush sash windows across Hampshire, Surrey and Berkshire from its base in Fleet.

The name confuses a lot of people, because “sash” makes most homeowners think of sliding sash windows. This guide explains what a flush sash window really is, how it compares with sliding sash and standard casement windows, which homes suit it, and what to ask before you buy.

What is a flush sash window

In window making, the sash is simply the part of the window that holds the glass and opens. On a standard uPVC casement, the sash closes against the outside of the frame and overlaps it, so you can see a stepped edge. On a flush sash window, the sash closes into the frame and finishes flat with it, the way joiners have made timber casements for generations.

That is why you will see the same product called a flush sash window, a flush casement window or a flush fit window. They all describe a hinged casement with a flat, flush face. At Cristal Windows we list them as uPVC flush casement windows, made with the REHAU Rio system.

Flush sash is not a sliding sash

A flush sash window opens on hinges, outwards, like any casement. A sliding sash window is a different design: two sashes slide up and down past each other in one frame, the style you see on Victorian and Georgian houses. If you want the vertical sliding look, you need a uPVC sliding sash window rather than a flush sash.

Flush sash vs standard casement vs sliding sash

All three styles can be double glazed, made to measure and finished in colours and wood-effect foils. The main differences are how they look and how they open.

Standard uPVC casement: hinged sash that overlaps the frame. A clean, modern look and usually the most budget friendly option.
Flush sash (flush casement): hinged sash that sits level with the frame. A timber look with uPVC upkeep, often chosen for cottages, period style homes and extensions.
Sliding sash: two sashes slide vertically on a spring balance. The traditional choice for Victorian and Georgian properties, and generally dearer like for like because of the mechanism and the deeper frame.

If you are weighing up hinged and sliding styles in more depth, our guide to sash windows vs casement windows covers ventilation, cost and which style suits which kind of house.

Why homeowners choose uPVC flush sash windows

Most people come to flush sash windows because they want the look of timber without the painting, sanding and rot that timber windows bring. Here is what you get with the flush windows Cristal Windows fits.

The look of a traditional timber window

The flat face is the biggest visual difference, but the details matter too. Wood-effect foils, a choice of colours and finishes, and authentic hardware such as teardrop and monkey tail handles all help a flush sash window pass for a traditional joinery made window from the street.

Low maintenance

Unlike timber, uPVC does not need repainting or treating. A simple wipe keeps the frames looking new, which is a big part of why flush sash windows are a popular timber replacement.

Warm and energy efficient

Our uPVC flush casement windows are rated ‘A’ for energy efficiency, so they help keep heat in and can reduce the energy you use to heat your home. Triple glazing is also available if you want to go further.

Secure as standard

Every window comes with a multi-point locking system as standard. Cristal Windows is a Yale Trusted Installer, and the Yale locks we fit come with the Yale Lifetime Security Guarantee.

Which homes suit flush sash windows

Flush sash windows work on a wider range of houses than many people expect. Around Hampshire, Surrey and Berkshire we see them chosen for three main types of property.

Cottages and period style homes where the original windows were timber casements and the owner wants the same flat profile back.
Post-war and later homes where a homeowner wants something smarter than a standard casement. In Fleet and the Farnborough and Camberley area, flush casements have become an increasingly popular upgrade.
Extensions and new builds where the windows need to match an older main house or simply look more crafted.

Conservation areas and listed buildings

Replacing windows on an ordinary house usually does not need planning permission. Conservation areas and listed buildings are the main exceptions, and every council sets its own rules, so the right answer depends on your address. Some councils are happy with uPVC that looks like timber, while listed buildings often need genuine timber. Cristal Windows also supplies timber windows for projects where only timber will do. Our guide for homeowners in conservation areas explains what to check, and our free survey flags any restrictions before you order.

What to ask before you buy flush sash windows

Flush windows are made to measure and fitted into your existing openings like other replacement windows. A few questions will help you compare quotes fairly.

Which system is it? Ask whose profile is used. Cristal Windows fits the REHAU Rio system and is a REHAU Authorised Partner.
Which colours, foils and handles are included? Wood-effect foils and period handles make the biggest difference to the finished look.
What glazing is quoted? Check whether the price is for double or triple glazing, and whether Georgian bars are included if you want them.
Who fits them? Choose a FENSA registered installer, so the work is certified as meeting Building Regulations without a separate application to building control.

Price depends on the size and number of windows, the colour and foil, the glazing and the hardware, so the most accurate figure comes from your own measurements. You can get a quick idea of cost with our instant online quote.

Flush sash windows from Cristal Windows

Cristal Windows is a family run supply and install company in Fleet with more than 40 years of experience. We are FENSA registered, a Which? Trusted Trader and members of the GGF, and we fit windows within about 30 miles of Fleet, including Farnborough, Farnham, Aldershot, Camberley, Basingstoke, Guildford, Woking, Alton and Haslemere.

Every installation starts with a free survey, so you can see colours, foils and handles and get a fixed quote before you decide.