Flush Casement vs Flush Sash
If you’re choosing new windows, you’ve probably come across the terms flush casement and flush sash. They sound similar, and they are, but there are a few important differences that can affect how your home looks and performs.
At 6 Day Doors, we work with trade professionals across the UK to supply high-performance windows and doors with fast lead times. In this guide, we’ll break down the differences in a simple way so you can choose the right option for your project.
What is a Casement Window?
A casement window is the most common window style in the UK. It opens outwards on hinges, usually from the side or top.
Key features:
- The opening part (sash) protrudes slightly from the frame
- Often called “lipped” or “stormproof” windows
- Designed to deflect rainwater away from the home
- Very versatile and suits most property types
Explore our range of Aluminium Casement Windows.
What is a Flush Casement (Flush Sash) Window?
A flush casement window (often called a flush sash window) sits completely flat within the frame when closed. There is no lip or overlap.
Key features:
- Flush finish (flat, smooth appearance)
- Clean, modern lines
- Often used in contemporary or heritage-style designs
- Can replicate traditional timber windows
Explore our uPVC Flush Casement Windows and Aluminium Flush Casement Windows.
Standard casement (lipped design)
Standard casement (lipped design)
Flush casement (flush sash design)
Side-by-Side Comparison
Casement Windows
Flush Casement / Flush Sash
Which Style Looks Better?
This comes down to the style of your property.
Choose casement windows if:
- You want a classic, traditional look
- Your home is Victorian, Georgian, or older
- You like features like glazing bars
Choose flush casement (flush sash) if:
- You prefer a clean, modern design
- You want a minimalist finish
- You’re using colours like anthracite grey or black
- You want a timber-style look without the maintenance
For inspiration, view our Gallery.
Are Flush Casement Windows Weatherproof?
A common question is whether flush casement windows are as durable as standard casement windows.
The short answer: yes, they are.
While traditional casement windows are often called stormproof because of their lipped design, modern flush casement windows are engineered to perform just as well.
Why they still perform well:
- Advanced seals and gaskets
- High-quality glazing systems
- External cills to guide water away
- Precision manufacturing
Energy Efficiency: Is There a Difference?
In real terms, there’s very little difference between the two styles.
Both window types:
- Support double or triple glazing
- Achieve low U-values
- Help reduce heat loss
- Lower energy bills over time
Typical Costs (UK Guide)
Costs can vary depending on size, material, and specification, but here’s a rough guide:
Casement windows:
- uPVC: £60 – £600+ per window
- Aluminium: £239 – £1,200+
Flush casement / flush sash windows:
- uPVC: £60 – £800+ per window
- Aluminium: £385 – £1,500+
Why flush windows cost more:
- More complex manufacturing
- Premium design detailing
- Higher demand for modern aesthetics
Tip: Trade customers can often access better pricing and faster lead times when ordering in volume.
Pros and Cons
Casement windows – pros
✔ Cost-effective
✔ Strong weather protection
✔ Widely available
✔ Easy to maintain
Casement windows – cons
✘ Slightly bulkier look
✘ Less modern appearance
Flush casement / flush sash – pros
✔ Sleek, modern design
✔ Great for heritage replication
✔ Premium appearance
✔ Strong thermal performance
Flush casement / flush sash – cons
✘ Higher cost
✘ Slightly more specialised
What About Other Sash Window Styles?
If you’re comparing flush sash options, it’s worth understanding that “sash” can also refer to sliding sash windows, which are different again.
Vertical sliding sash windows:
- Open by sliding up and down
- Traditional for period homes
- Often used in conservation areas
Explore our range of uPVC Vertical Sliding Sash Windows
Which Should You Choose?
There isn’t a “better” option, just the right one for your project.
Go for casement if:
- You want value and versatility
- You’re working on traditional properties
- Budget is a key factor
Go for flush casement if:
- You want a premium, modern look
- You’re aiming for architectural styling
- Appearance is a top priority
Get Your Free Windows Quote
Understanding the difference between flush casement and flush sash windows comes down to one key detail: how the sash sits in the frame.
- Casement windows give you a traditional, practical solution
- Flush casement windows offer a modern, premium finish
Both deliver strong performance, energy efficiency, and long-term value.
At 6 Day Doors, we specialise in supplying high-performance trade windows and doors with fast, reliable delivery. Whether you’re working on a modern build or a heritage project, our range is designed to meet the demands of installers, developers, and trade professionals across the UK.
