A flush casement window closes with its opening sash sitting perfectly level with the outer frame, creating one flat, unbroken surface across the face of the window. There is no step, no overlap, no shadow line. The result is the clean, traditional look of painted timber joinery, now available in low-maintenance uPVC and aluminium. Fitted uPVC prices in 2026 start from £300 for a small opening and run to around £520 for a taller Victorian-era unit. You can build a full quote in the flush casement cost calculator. If you want to compare this style against the everyday alternative, the standard casement windows guide covers the stormproof casement in detail, and the casement window calculator prices those up.
What makes a flush casement different?
A standard casement window, often called a stormproof casement, is designed so that the opening sash overlaps the outer frame by a few millimetres. Viewed from outside, a slight step or rebate runs around the sash. This is practical: the overlap helps shed rainwater and is forgiving during manufacture because the frame and sash do not need to be perfectly co-planar. It is also why the stormproof casement became the default style in post-war British housing and remains the most common type installed today.
A flush casement is engineered differently. The sash closes into the frame so that their outer faces sit in the same plane. No overlap, no step. The weathertight seal is created by a compression gasket hidden within the rebate, so from outside all you see is the frame, the sash, and the glass. The result looks far closer to traditional painted hardwood joinery, which is precisely why flush casements are favoured on period properties, barn conversions, and rural buildings where a stormproof casement would look out of place.
Because the tolerances are tighter and the profile is more complex to extrude and fabricate, flush casements cost more to make and fit. As a rule of thumb, expect to pay roughly 30% more than you would for an equivalent standard casement in the same material and size. For most modern homes that premium is hard to justify, but for heritage settings it is money well spent.
People often come to me saying they want timber-look windows but do not want to repaint every few years. A flush uPVC casement in a woodgrain foil is the honest answer to that. It is not identical to painted timber, but from the pavement it convinces, and you never touch it with a paintbrush again.
Tom Bradley, FENSA-registered installer
Flush casement window costs in 2026
All prices below are for uPVC, fully fitted, and include removal of the existing window, silicone sealing, and a FENSA certificate. The three size points cover the most common residential openings. A 600 x 900 mm flush casement is the smallest standard size and the entry point for cost. A 1,200 x 1,200 mm unit is the typical lounge or dining room window. The 940 x 1,600 mm dimension suits taller Victorian-era openings common in period terraces, where the flush profile earns its premium most clearly.
| Window size | uPVC fitted | Typical |
|---|---|---|
| 600 x 900 mm | £300–£400 | £350 |
| 1,200 x 1,200 mm | £450–£550 | £500 |
| 940 x 1,600 mm | £470–£570 | £520 |
Source: DGCC 2026 dataset, cross-checked against Checkatrade and South Yorkshire Windows.
The cost premium over a standard casement
The price difference between a flush casement and a standard stormproof casement is consistent across materials. In uPVC, the premium of roughly 30% reflects the more complex profile, tighter manufacturing tolerances, and the additional fabrication time needed to ensure the sash closes truly flush. In aluminium, where profiles are already precision-extruded, the percentage difference is similar but the absolute cost is higher because the base price is greater.
Whether the premium is worth paying depends almost entirely on your home. On a modern semi or a post-war terrace, a standard casement gives you equivalent thermal performance, the same multipoint locking and a saving of roughly a third of the window bill. On a Victorian or Edwardian frontage, a Georgian farmhouse, or a barn conversion, the flush casement looks proportionate and appropriate in a way a stormproof unit simply does not. Our casement vs sash comparison covers the broader question of which traditional window family suits your home if you are still undecided.
Which homes suit flush casement windows?
Best Buy Flush casements are the right choice wherever a flat, clean, traditional profile matters. That covers:
- Period terraces (Victorian, Edwardian). A stormproof casement looks incongruous against the original brickwork and stone surrounds of these properties. The flush profile does not.
- Barn conversions and farmhouses. The flush, simply detailed sash echoes the large, uncluttered openings of agricultural buildings that have been brought into residential use.
- Conservation areas. Planning guidance in many conservation areas specifies a flush or near-flush profile to preserve street character. A stormproof casement may not meet the condition.
- Homeowners wanting timber aesthetics without timber maintenance. The flush uPVC casement in a foiled woodgrain finish is the closest the industry gets to timber-look without the repainting obligation.
Flush casements are less appropriate on 1970s or 1980s estates, new builds, or modern extensions where the standard stormproof casement is already the norm and the premium earns nothing visually. For sash-fronted period properties, read our sash windows guide before committing to a casement at all. A vertical sliding sash is often the architecturally correct choice where the flush casement is only an acceptable compromise.
When a flush casement is the wrong choice
It depends If your home is a post-war semi, a 1960s bungalow, or a new build, a standard casement will perform identically and cost materially less. The flush profile solves a visual problem on heritage buildings. On a modern home that has no such problem, the extra cost delivers nothing you will notice from day to day.
There is also a supply-and-fit consideration. Flush casement fabricators are less common than stormproof fabricators, so you may receive fewer competitive quotes. Fewer quotes typically mean less downward pressure on price. Always obtain at least three written, itemised quotes before committing, and confirm that each one includes removal, FENSA registration, and a minimum ten-year guarantee on the sealed unit.
My advice on flush casements is straightforward: use them where the house earns them. Do not put them on a 1980s box just because they look nice in the brochure. But on a stone cottage or a brick terrace with original lintels, they make all the difference between a job that looks right and one that just looks done.
Tom Bradley, FENSA-registered installer
Energy performance and building regulations
A flush casement achieves the same thermal performance as an equivalent stormproof casement. The compression gasket creates a tight, weathertight seal when the multipoint lock is engaged, and modern uPVC flush casements are routinely manufactured to achieve a U-value of 1.4 W/m²K or below, meeting the Part L building regulations requirement for replacement windows in England. The flush design does not compromise energy efficiency.
Replacement windows must be installed by a FENSA-registered company or notified to your local authority building control department. A FENSA-registered installer will issue a certificate on completion, which you will need when you sell the property. Any reputable flush casement installer should be able to provide this as standard.
The verdict
For the right home, the flush casement is the most appropriate uPVC or aluminium window style available: it performs as well as a standard casement, lasts as long, needs as little maintenance, and looks significantly more in keeping on period and heritage properties. The 30% cost premium is real but justified where the house calls for it. Start with the flush casement cost calculator to price your own openings, or browse the full guides library if you are still deciding which window style suits your home.
Frequently asked questions
A flush casement is a hinged window where the opening sash sits level and flat with the outer frame when closed, creating a single, unbroken plane across the face of the window. A standard stormproof casement has the sash overlapping and standing slightly proud of the frame. Flush casements originated in traditional timber joinery and are now widely available in uPVC and aluminium.
A fitted uPVC flush casement costs £300 to £570 depending on size. A small 600 x 900 mm opening runs £300 to £400 (around £350 typical); a standard 1,200 x 1,200 mm window costs £450 to £550 (around £500); and a larger 940 x 1,600 mm unit costs £470 to £570 (around £520). All prices are fully fitted and include removal, sealing, and a FENSA certificate.
Yes. A flush casement costs roughly 30% more than an equivalent standard (stormproof) casement in the same material and size. The premium reflects the tighter engineering tolerances needed to achieve a flat, flush close, plus the more complex frame profile.
A stormproof casement has the opening sash overlapping the outer frame, leaving a slight step or rebate visible from outside. This overlap helps shed rain but gives a more utilitarian appearance. A flush casement closes level with the outer frame with no step or shadow line, giving it the clean, flat look of traditional painted timber joinery.
Flush casements suit period properties, Victorian and Edwardian terraces, barn conversions, farmhouses, and rural or heritage homes where the flat, traditional profile is more in keeping than a standard stormproof casement. They are also popular with homeowners who want the low maintenance of uPVC or aluminium but prefer a window that does not look overtly modern.
Modern uPVC flush casements are available in a wide range of woodgrain foils, including oak, rosewood and Anthracite Grey. The flat, seamless face more closely mimics the look of painted timber than a standard casement with its protruding sash. They will not deceive an expert at close range, but they are a convincing and low-maintenance alternative in most settings.
In most cases, no. Replacing like-for-like windows is permitted development in England, Wales and Scotland. However, if you are in a conservation area, an Area of Outstanding Natural Beauty, or a listed building, you may need consent. Always check with your local planning authority before ordering.
Yes. Like a standard casement, a modern flush casement presses its sash against a compression seal when locked, achieving a tight, weathertight close. An A-rated uPVC flush casement comfortably meets the Part L requirement of a U-value of 1.4 W/m²K or lower. You do not sacrifice thermal performance for the heritage look.