Slimline Aluminium Casement Windows | 35mm Frame, Concealed Hinges, 85% Glass | SGL
Shaanxi SGL Doors&Windows Technology Co., Ltd. is one of the most reliable manufacturers and suppliers of slimline aluminium casement windows | 35mm frame, concealed hinges, 85% glass | sgl in China, also supports customized service. Please feel free to wholesale high quality slimline aluminium casement windows | 35mm frame, concealed hinges, 85% glass | sgl for sale here from our factory. If you have any enquiry about pricelist and quotation, please feel free to email us.
Product Description
The Engineering Challenge of Slimline Casement Windows
Narrowing an aluminium window frame from 60mm to 35mm is not simply a matter of cutting material. The frame must still carry wind loads, support the weight of the glass, house thermal break strips, accommodate multi-point locking hardware, and maintain compression seals - all within a profile that is barely wider than a standard door handle.
SGL solves this through high-strength 6063-T5 alloy extrusions with 2.0-2.5mm wall thickness and multi-chamber internal geometry. The chambers increase sectional inertia without adding visible width, allowing the frame to resist bending under wind pressure while the 35mm face remains clean. The thermal break is a specially designed I-shape PA66 strip that fits within the narrow cavity while maintaining the same thermal separation as wider profiles.
Why Casement - Not Sliding - for Slimline Designs
Slimline sliding windows sacrifice airtightness because the sash must slide past the frame, leaving a gap that cannot be fully sealed. Slimline casement windows do not have this limitation: the sash closes against the frame with a compression seal, achieving the same Class A airtightness as standard-width casements. For architects designing energy-efficient buildings with minimalist aesthetics, slimline casement is the only opening type that delivers both clean sightlines and certified performance.
Slimline Engineering Features
35mm Frame with 85% Glass-to-Frame Ratio
A standard casement window has 70-75% glass-to-frame ratio. SGL slimline casement windows increase this to 85% - meaning 10% more daylight and 10% less visual interruption. On a 3m x 2.4m window wall, that is an extra 0.72 m² of unobstructed glass. For residential towers and commercial facades, this difference transforms interiors.
Concealed Stainless Steel Hinges
Visible hinges break the clean lines of a slimline frame. SGL uses fully concealed friction hinges manufactured from 304 stainless steel, rated to 80kg per sash with 100,000 cycle testing. The hinge is recessed into the frame and sash, completely invisible when closed. Three-dimensional adjustment (height, compression, lateral) allows perfect alignment during installation and compensation for building settlement over time.
Hidden Multi-Point Locking
The locking keeps are concealed within the frame profile - no visible shootbolts, no face-mounted hardware. When the handle is turned, concealed locking points engage at 3-5 positions along the sash perimeter. From the exterior, the window presents a perfectly flat, uninterrupted surface. From the interior, only the handle is visible. This is the standard specification, not an upgrade.
Dual-Lip EPDM Compression Seal
Narrow frames leave less space for seals. SGL uses a specially formulated dual-lip EPDM gasket: the outer lip seals against water ingress, the inner lip seals against air leakage. The gasket is co-extruded with a rigid spine that clips into a dedicated channel in the aluminium profile, ensuring it cannot dislodge under repeated opening cycles. Tested to maintain elasticity from −40°C to +120°C.
28mm Mullions for Multi-Light Windows
When multiple casement sashes are combined in a single frame, the mullion between them is typically 60-80mm - a heavy visual element. SGL slimline mullions are just 28mm visible width while maintaining structural integrity for adjacent sashes up to 1,200mm wide. This makes slimline casement windows ideal for traditional multi-light designs (grid patterns) that would otherwise look heavy and industrial.
35mm Corner Posts for Continuous Sightlines
Corner and bay window configurations typically require bulky corner posts (80-100mm) that interrupt the view. SGL slimline corner posts are 35mm visible width - identical to the main frame - available in 90-degree and 135-degree angles. The result is a continuous glass surface around building corners with no visual obstruction at the junction.
Slimline Casement vs Standard Casement
Slimline Casement (35mm frame)
• 85% glass-to-frame ratio
• Concealed hinges and locks
• 28mm mullions
• 35mm corner posts
• Modern minimalist aesthetic
• Ideal for contemporary architecture
• Slightly higher cost (+15-20%)
Standard Casement (60mm frame)
• 70-75% glass-to-frame ratio
• Exposed hinges and face-mounted locks
• 60-80mm mullions
• 80-100mm corner posts
• Traditional / industrial aesthetic
• Cost-effective for budget projects
• Same airtightness and water tightnes
Suitable For
Slimline casement windows are specified where the frame must disappear and the view must dominate:
- Contemporary Residential Towers
- Luxury Apartments & Penthouses
- Floor-to-Ceiling Window Walls
- Corner & Bay Window Configurations
- Glass Box Extensions
- High-End Commercial Facades
- Boutique Hotels & Resorts
- Heritage Building Renovations (Modern Insert)
our aluminum window Application
our factory
Client Visit
Frequently Asked Questions
Q: Q1: What is a slimline casement window?
A: A slimline casement window is a hinged window system with an ultra-narrow visible frame - typically 35-40mm - designed to maximize glass area and create a clean, minimalist aesthetic. Unlike standard casement windows with 60-70mm frames, slimline versions use advanced aluminium extrusion and concealed hardware to reduce the visible profile while maintaining structural strength, airtightness, and thermal performance. SGL's slimline casement windows achieve 85% glass-to-frame ratio.
Q: Q2: How do slimline casement windows seal properly with such narrow frames?
A: Sealing in narrow frames requires precise engineering. SGL uses continuous EPDM compression gaskets with a dual-lip design - one lip seals against the glass, the other against the sash. The multi-point locking system engages 3-5 concealed keeps along the sash perimeter, applying uniform pressure to compress the gasket fully. Independent testing confirms Class A airtightness (EN 12207) and Class A water tightness (EN 12208) even at 700 Pa pressure - comparable to standard-width frames.
Q: Q3: What is the maximum size for a slimline casement window?
A: Our standard slimline casement windows support sash sizes up to 1,200mm (width) x 2,400mm (height). The limiting factor is not the frame width but the hinge system - concealed friction hinges rated to 80kg per sash. For oversized applications (e.g., floor-to-ceiling pivot windows), we specify heavy-duty concealed hinges with 120kg capacity or switch to a slimline tilt-and-turn mechanism that distributes load across the entire frame perimeter.
Q: Q4: Are concealed hinges as strong as exposed hinges?
A: Yes. SGL's concealed friction hinges are manufactured from stainless steel 304 and rated to 80kg per sash with 100,000 cycle testing. The hinge is recessed into the frame and sash profiles, making it invisible when the window is closed. Three-dimensional adjustment (height, compression, lateral) ensures perfect alignment after installation. For comparison, a standard exposed butt hinge is typically rated to 60-70kg. Concealed hinges are stronger, more secure, and aesthetically superior.
Q: Q5: Can slimline casement windows be used in corner or bay window configurations?
A: Yes. Slimline casement windows are ideal for corner and bay configurations because the narrow frame minimizes the visual interruption at the junction. We offer 90-degree and 135-degree corner posts with a visible width of just 35mm - the same as the main frame - creating a continuous, frameless appearance. For bay windows, the slim mullion between adjacent casements can be as narrow as 28mm, maximizing the uninterrupted glass area.
Project Case Studies
We provide one-stop door and window solutions for individual buyers, contractors, renovation companies, and more.
Our address
No. 2 Group, Fumiao Village, Laojun Town, Hantai District, Hanzhong City, Shaanxi Province, China
Phone Number
+86 13335450021
sgl-factory@sgl-doors-windows.com
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Slimline Casement Specifications
| Specification | Details |
|---|---|
| Visible Frame Width | 35mm (ultra-slim) |
| Frame Depth | 60mm / 75mm |
| Glass-to-Frame Ratio | ≥ 85% |
| Frame Material | Aluminium Alloy 6063-T5 |
| Profile Thickness | 2.0mm / 2.5mm |
| Opening Type | Inward / Outward Casement |
| Hinge System | Concealed friction hinges (304 SS, 80kg capacity) |
| Locking System | Concealed multi-point lock with hidden keeps |
| Glass Configuration | 5+20A+5 Double / 5+12A+5+12A+5 Triple |
| Thermal Break | PA66 Polyamide + 25% Glass Fiber |
| U-Value | 1.4 – 1.8 W/m²K |
| Air Tightness | Class A (EN 12207) |
| Water Tightness | Class A (EN 12208) - 700 Pa tested |
| Sound Insulation | 38 – 45 dB |
| Max Sash Size | 1,200mm (W) x 2,400mm (H) |
| Corner Post Width | 35mm (90° and 135°) |
| Mullion Width | 28mm (minimum) |
| Surface Finish | Powder Coating / Anodizing / Wood Grain |
| Certifications | CE (EN 14351-1), ISO 9001:2015 |
| Warranty | 10-year frame / 5-year hardware & glass |
- 35mm visible frame width - 40% narrower than standard 60mm frames
- 85% glass-to-frame ratio - maximizes natural light and unobstructed views
- Concealed stainless steel hinges - 80kg capacity, 3D adjustable, invisible when closed
- Hidden multi-point locking - security hardware completely concealed from view
- Class A airtight/water tight - dual-lip EPDM seals, tested to 700 Pa
- Thermal break as standard - PA66 + 25% GF, U-value 1.4-1.8 W/m²K
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