Flush Sash Windows
Sealed Tight, Fitted Right™ · Insulation Tape on Brick-to-Brick Installs
Liniar Flush sash windows sit flush within the frame rather than proud of it, giving a clean, seamless look that closely replicates traditional timber windows — ideal for period and conservation-area properties, and just as at home on a modern build. As a Liniar-approved installer, we fit both flush casement systems available: the R70 Original Flush Sash and the R80 Resurgence, so you can choose the look, performance, and budget that’s right for your home.
Two Flush Glaze Systems
R70 Original Flush Sash
The R70 Original features a 70mm frame and a 50mm sash — a genuine, cost-effective flush window for period and conservation-area properties. A single rebated weather seal with a brush pile in the shadow gap keeps the window weathertight, and the frame and sash can be finished with a welded joint (modern, clean look) for a contemporary finish.
- U-values: 1.3 W/m²K (double glazed) / 0.9 W/m²K (triple glazed)
- Energy rating: up to A+
- Glazing: 28mm glazing units only
- Foiling: applied to the outer frame only — always white on the inside
The image illustrates the 70mm flush-glazed finish with equal sightlines, complemented on brick-to-brick installations by insulation tape that fills all gaps and expands to provide a watertight seal with clean, straight finishing lines. This method removes the need for mastic or additional trims.
R80 Resurgence Flush Sash
Our premium flush sash window. Built on an 80mm frame with a 70mm sash, the R80 Resurgence is designed to give the most authentic timber-window appearance available in a uPVC flush system — especially when the window is open. A double rebated seal with a patented co-extruded bubble gasket sits tucked behind the sash, completely invisible from inside or outside when the window is closed, so there’s no brush pile to go misshapen or untidy over time.
- U-values: as low as 0.84 W/m²K (whole window)
- Energy rating: up to A+
- Best acoustic rating: 37dB (Rw)
- Glazing: 28mm, 36mm or 40mm glazing units — giving flexibility for new-build compliance or homes wanting extra thermal or acoustic performance
- Foiling: applied to the frame and the sash interior, so the timber-look finish stays consistent even when the window is open — a genuine advantage for period and heritage properties
- Available with welded or mechanical joints (mechanically jointed timber-look frames are only offered by a limited number of fabricators).
How Much Outside Noise Do Flush Sash Windows Block?
Noise reduction depends on the glazing unit fitted rather than the frame alone, but the frame’s seal design plays a real part too. Here’s how the R70 and R80 compare:
| Window System | Glazing | Acoustic Rating | Noise Reduction | Best For | Key Benefit |
| R70 Original | Standard 28mm double glazed | 32–33 dB | Standard reduction | Normal residential traffic | Reliable everyday sound insulation |
| R70 Original | 28mm double glazed with acoustic laminate | 35 dB | Enhanced reduction | Busier residential streets | Improved noise control |
| R80 Resurgence | Standard 28mm double glazed | 33–34 dB | Improved isolation | Homes needing better sealing performance | Double-rebated seal improves comfort |
| R80 Resurgence | 36mm triple glazed | 35 dB | High-performance isolation | Continuous traffic, busy roads | 36mm/40mm units unlock stronger noise reduction |
| R80 Resurgence | 40mm triple glazed with acoustic laminate | Acoustic Rating: 37 dB | Premium noise dampening | Best For: Homes near main roads, railways or flight paths | Enhanced acoustic performance in a standard uPVC flush sash window. |
The Liniar R80 Resurgence flush sash window can accommodate 36mm and 40mm glazing units, compared with the R70’s 28mm glazing limit. This allows for enhanced acoustic glazing and higher levels of noise reduction, especially when combined with the R80 double-rebated seal, which helps close the small air paths where sound can travel. On brick-to-brick installations, where our insulation tape is fitted as standard, the result is a high-performance uPVC flush window with improved acoustic insulation, airtight sealing, weather protection, thermal efficiency and long-term energy-saving benefits
This image shows the R80 flush-glazed finish, designed to create a clean, modern appearance with equal sightlines and a premium flush profile. The R80 system is ideal for homeowners looking for stylish uPVC flush glazing with improved weather protection, energy efficiency and a neat, low-maintenance finish. On brick-to-brick installations, insulation tape is used as standard to fill gaps and expand around the frame, helping to create a watertight seal without the need for visible mastic or additional trims.
Which Flush Sash Window Is Right for You?
Choose the R70 Original if you want a genuine flush window for a period or conservation-area property, a double-rebated seal isn’t specified, or budget is the main consideration.
Choose the R80 Resurgence if you want the most authentic timber appearance — especially with the window open and you have a foil finish, as the foil is wrapped around the frame inside, so no white shows — along with superior weatherproofing, better noise reduction, or the flexibility of thicker glazing units for higher thermal performance.
Flush Sash Window Colours
Both systems are available in white and cream, plus a wide range of foiled finishes including 7016 Grey, Rosewood, Black Brown, and more.
Liniar 70mm Flush Sash Colours
The standard 70mm flush sash window profile is traditionally stocked in a wider variety of clean heritages and greys:
- Solid Whites & Creams: White (RAL 9003) and Classic Cream.
- Modern Greys: 7016 Anthracite Grey, Agate Grey, and Gale Grey Finesse.
- Traditional Woodgrains: Irish Oak, Golden Oak, Rosewood, and Black Brown.
- Heritage Accent: Chartwell Green.
Liniar 80mm Resurgence Flush Sash Colours
The flagship 80mm Resurgence flush sash window system—noted for its double-rebated timber-replica appearance—carries a curated palette that complements its premium architectural structure:
- Base Solids: Standard White, RAL 9003 White, and Cream.
- Architectural Greys: 7016 Grey, Agate Grey, and textured Gale Grey Finesse.
- Premium Foils: Classic Rosewood, Black Brown, and the deeply textured Anteak woodgrain.
Textured Anteak woodgrain is a popular light-to-medium brown uPVC foil finish for Liniar Resurgence 80mm flush sash windows and doors, designed to replicate the appearance of natural timber on window frames, doors, fascias and trims. This premium timber-effect finish offers a distinctive alternative to Irish Oak, making it ideal for homeowners looking for low-maintenance uPVC flush windows with traditional character, modern energy efficiency and an authentic timber woodgrain appearance.
Bespoke and special-order colour configurations (including contrasting combinations where the exterior is a different shade than the indoor frame) are available on longer lead times across both frame types.
Flush Sash vs Flush Casement Windows: What’s the Difference?
‘Flush sash’ and ‘flush casement’ are largely used to describe the same style of window — one where the sash sits flush with the outer frame rather than protruding from it, giving the traditional timber look. Liniar markets its R70 Original and R80 Resurgence ranges as flush sash systems, though you’ll also see the same style described elsewhere as flush casement windows. Whichever term you search for, we install the same Liniar-approved systems either way.
Flush Sash Window FAQs
What is a flush sash window?
A flush sash window has its opening sash fitted flush with the outer frame, rather than sitting proud of it like a standard casement window. This gives a clean, traditional look that closely replicates timber windows, which is why they’re popular on period and conservation-area properties as well as modern builds.
What’s the difference between a flush sash and a flush casement window?
In practice, nothing — they’re two names for the same style of window. ‘Flush sash’ tends to be the term UK homeowners search for, while ‘flush casement’ is also widely used by manufacturers and installers, Liniar included. We fit the same R70 and R80 systems regardless of which term you use.
Are flush sash windows suitable for conservation areas?
Yes — their flush, timber-replicating profile is one of the main reasons they’re chosen for period properties and conservation areas. If your property is listed or in a conservation area, it’s worth checking with your local planning authority before work begins; see the Planning Portal’s guidance on windows and doors for more detail.
Why Choose Us for Your Flush Sash Windows
We fit flush sash windows across East London, South London, North London and South Essex, with no hard sell — we’ll help you choose the flush casement system that suits your home and your budget, with no pressure to decide on the day.
Want to know More?
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