Slimline casement
Side-hung sashes with compression gaskets and multi-point locks. Excellent air and water tightness for bedrooms, kitchens and villa facades; hidden-sash versions put the sash behind the outer frame.
Window systems
Slimline Aluminium Windows
Slimline aluminium windows use narrow, precisely engineered frames so more of each opening is glass: more daylight, wider views and the clean lines modern and heritage architecture both call for. With thermal breaks, Low-E glazing and multiple gaskets, they reach the energy and weather performance of standard systems. Metline supplies slimline casement, fixed, tilt and turn, sliding and steel-look window profiles and accessories to window fabricators for residential, renovation and commercial projects worldwide.
- Profiles
- 6060-T66 / 6063-T6, about 2.0 mm walls
- Window types
- Casement, fixed, tilt-turn, sliding
- Thermal break
- PA66 GF25, about 24 mm
- Typical Uw
- About 1.3 – 1.8 W/m²K
What are slimline aluminium windows?
A slimline window is defined by its sightline: the combined width of outer frame and sash you see from inside or out. Where a standard aluminium casement might show 100 – 130 mm of frame and sash together, slimline systems reduce this to roughly 50 – 80 mm, and fixed lights with frames recessed into the wall can show only 20 – 35 mm. Mullions and transoms are similarly reduced so that a multi-pane window reads as a sheet of glass divided by fine lines.
The narrow look is made possible by aluminium's stiffness and strength. A slim aluminium section can carry heavy double or triple glazing and resist wind without the bulk that uPVC needs (uPVC frames rely on steel reinforcement inside wide chambers) or the depth of timber. Slimline systems typically achieve this by moving material into depth rather than face width, using concealed hinges and locks, and hiding the sash behind the outer frame or the glass.
Two broad families exist. Contemporary slimline windows aim for minimal frames and maximum glass on modern houses, apartments and offices. Steel-look or heritage slimline windows reproduce the fine frames and glazing bars of traditional steel windows, offering a lighter, insulated and lower-maintenance replacement in older buildings and conservation areas.
Types of slimline aluminium window
Slimline fixed window
Non-opening frames with the narrowest sightlines, used for picture windows, stairwells, corner glazing and shop displays.
Slimline tilt and turn
Tilts inwards for secure ventilation and turns inwards for cleaning. Popular in Europe and for high-rise housing where outward-opening sashes are unsafe.
Slimline sliding window
Horizontal sliding sashes that save space on balconies and in kitchens. Sealing depends on the system; lift-and-slide or tight-seal tracks perform best.
Awning / top-hung window
Opens outward from the bottom edge for ventilation in light rain; useful in bathrooms, stairwells and above fixed panes.
Vertical sliding (sash-style)
Aluminium windows with the look of traditional box sash windows for period terraces and heritage renovation.
Rooflights
Slim-framed fixed or opening glazing in flat or pitched roofs for lofts and extensions; drainage and glass specification are critical.
Steel-look heritage window
Black narrow frames with glazing bars and stepped profiles that replicate steel windows while adding thermal breaks and double glazing.
Typical slimline window system specifications
Slimline systems vary, but most quality series fall within the ranges below. These describe typical systems in this class rather than guaranteed figures; ask for the data sheet and test reports of the specific system proposed.
| Item | Typical range |
|---|---|
| Profile alloy | 6060-T66 (Europe) or 6063-T6; high-precision extrusions with tight dimensional tolerance |
| Profile wall thickness | About 1.8 – 2.0 mm on main frame and sash sections |
| Frame depth | About 65 – 90 mm |
| Combined sightline (frame + sash) | About 50 – 80 mm for opening lights; 20 – 35 mm for recessed fixed lights |
| Thermal break | PA66 GF25 polyamide strips, typically about 20 – 24 mm, in frame and sash |
| Glazing | Double IGU about 24 – 32 mm (e.g. 5 / 19 / 5 or 6 / 16 / 6) or triple about 36 – 44 mm |
| Hardware | Euro-groove concealed hinges and multi-point locks |
| Gaskets | EPDM co-extruded or moulded gaskets, often with a centre gasket |
| Typical Uw | About 1.3 – 1.8 W/m²K with Low-E double glazing; lower with triple glazing |
| Acoustic reduction | About 30 – 40 dB Rw depending on glass build-up |
Corners are mechanically crimped or pinned and injected with two-part adhesive, so the frame stays square and sealed. Mullion-to-frame joints use cast or machined connectors with sealing pads. Drainage is routed through concealed slots behind cover caps, keeping the facade free of visible weep holes.
Glass, thermal break, sealing and hardware
A slimline window is only as good as its configuration. The narrower the frame, the larger the share of the window that is glass, so glass choice has an even bigger effect on performance than in standard windows.
| Glass option | Best for | Benefit |
|---|---|---|
| Low-E double glazing with argon | Most residential and commercial projects | Ug around 1.0 – 1.1 W/m²K |
| Triple glazing | Cold climates and low-energy buildings | Ug around 0.5 – 0.7 W/m²K; check sash weight |
| Solar-control Low-E | Hot or sunny regions, large west-facing glass | Reduces solar heat gain and glare |
| Laminated glass | Ground floors, accessible windows, low sills | Safety and security; holds together if broken |
| Acoustic laminated glass | Hotels, apartments near roads or rail | Higher sound reduction with asymmetric panes |
| Low-iron glass | Villas and premium view windows | Clearer, less green appearance |
| Self-cleaning coatings | Large or hard-to-reach glass | Less frequent cleaning |
- Warm-edge spacers reduce heat loss and condensation at the glass edge, which matters more when frames are slim.
- Gaskets in two or three lines (outer, centre and inner) separate the drained, pressure-equalised zone from the room.
- Concealed hardware keeps hinges inside the profile; check the maximum sash weight rating, especially with triple glazing.
- Insect screens and vents can be integrated, but trickle vents and screen frames add visible width; plan them early.
Performance classes and standards
Performance is classified by standard tests. Ask for the classes achieved by the actual system and size, not a smaller test sample.
| Property | Europe (EN 14351-1) | North America |
|---|---|---|
| Air permeability | EN 12207, classes 1 – 4 (class 4 is the tightest) | ASTM E283 |
| Watertightness | EN 12208, classes 1A – 9A, then E750 and above | ASTM E331 / E547 |
| Wind resistance | EN 12210, classes 1 – 5 with deflection A, B or C; e.g. C5 at 2000 Pa test pressure | ASTM E330, design pressure in NAFS |
| Thermal transmittance | EN ISO 10077-1 / -2 (Uw) | NFRC 100 (U-factor) |
| Acoustic | EN ISO 10140 test, EN ISO 717-1 rating (Rw) | ASTM E90 / E1332 (STC, OITC) |
| Burglary resistance | EN 1627 resistance classes | ASTM F588 |
For high-rise or exposed sites, the wind and water classes usually govern the choice of system more than the sightline target. A slim system with a proven high wind class and a tested large size is a safer specification than the narrowest frame available.
Slimline aluminium vs uPVC, timber and steel windows
| Material | Main advantage | Limitation | Best for |
|---|---|---|---|
| Slimline aluminium | Narrow, strong frames; durable finishes; any colour | Higher cost than uPVC | Modern homes, villas, apartments, commercial projects |
| uPVC | Low cost, good insulation | Bulky frames; colours limited; softens in strong heat | Budget residential replacement |
| Timber | Warm natural appearance, good insulation | Regular maintenance; frames wider than aluminium | Traditional homes, warm interiors |
| Steel | The slimmest traditional frames, very strong | Heavy, costly, prone to rust, poor insulation unless thermally broken | Listed buildings, industrial style |
| Steel-look aluminium | Steel appearance with thermal break and low maintenance | Slightly deeper than steel; needs good detailing | Heritage renovation, black-frame projects |
For conservation areas and listed buildings, local planning authorities often accept steel-look aluminium windows when sightlines, glazing bar layout and opening method match the originals. Provide sections and elevations comparing old and new profiles when seeking approval.
When to be careful with ultra-slim frames
- Large panes under high wind: may need deeper mullions, reinforced profiles or smaller panes.
- Replacement openings: the new frame must fit the existing wall depth and tolerances; the slimmest outer frame does not always suit an uneven opening.
- Ventilation requirements: regulations may require trickle vents or larger opening areas, adding visible frame.
- High acoustic or thermal targets: thicker glass needs deeper glazing rebates and stronger hardware, which can widen frames.
- Budget: concealed hardware, special glass, custom colours and dual finishes add cost; standard narrow frames may be the better value.
Finishes and colours for slimline windows
| Finish | Character | Where to use |
|---|---|---|
| Powder coating | Any RAL colour, matt to gloss, textured options | Most residential and commercial projects |
| Anodising | Metallic or black anodised, hard surface | Modern facades wanting a metal look |
| PVDF coating | Excellent UV and colour retention | Coastal, humid and high-UV sites |
| Woodgrain | Timber appearance | Villas and heritage-style interiors |
| Dual colour | Different inside and outside colours on thermal break profiles | Dark exterior with white or light interior |
Matt black, anthracite grey and textured black are the most popular choices for slimline and steel-look windows, because dark frames visually recede and emphasise the glass. White suits bright interiors and minimalist apartments.
Information for an accurate quotation
- ProjectCountry and location, new build or renovation, building type and height, coastal or inland.
- WindowsTypes, opening directions, opening sizes or drawings, and quantities.
- PerformanceThermal, acoustic, security and weather requirements, plus any heritage or planning constraints.
- Finish and glassColour and finish, glass build-up, hardware and screen requirements.
- DeliveryTarget schedule, packing and labelling, destination port; Metline confirms EXW, FOB, CIF or DAP terms and supplies packing lists and documents.
References and standards
- EN 14351-1 – Windows and doors: product standard, performance characteristics
- EN 12207, EN 12208 and EN 12210 – Windows and doors: classification of air permeability, watertightness and resistance to wind load
- EN ISO 10077-2 – Thermal performance of windows, doors and shutters: numerical method for frames
- AAMA/WDMA/CSA 101/I.S.2/A440 – North American Fenestration Standard
- EN 755-2 – Aluminium and aluminium alloys: extruded rod/bar, tube and profiles, mechanical properties
Slimline aluminium (aluminum) windows: FAQ
Are slimline aluminium windows energy efficient?
Yes, when they are thermally broken and fitted with Low-E insulating glass and warm-edge spacers. Typical slimline systems achieve Uw values around 1.3 – 1.8 W/m²K with double glazing, and lower with triple glazing, which meets many current energy codes.
What affects the sightline of a slim aluminium window?
The window type, whether the sash is visible or hidden, frame depth, glass weight, hardware, mullion and transom design, and how the frame is installed in the wall. Opening sashes always show more frame than fixed lights.
Are slimline aluminium windows suitable for heritage properties?
Yes. Steel-look slimline windows reproduce the narrow frames and glazing bars of traditional steel windows with modern insulation, and many planning authorities accept them in conservation areas. Confirm with the local authority before ordering.
Are slim frames strong enough for high-rise buildings?
Slimline systems are available with high wind resistance classes, but very large panes at height may need deeper sections or reinforced mullions. Choose a system with test results at your design pressure and size.
Can slimline windows have insect screens?
Yes. Fixed, roller or sliding insect screens can be integrated. They add a little visible frame, so plan screen positions with the window design.
Do you supply slimline windows for export and US projects?
We supply the slimline window profiles, not finished windows. Metline ships profiles and hardware worldwide, with finishes and sections chosen for the target market, and project packing, labelling and documentation for your fabricator.
Specifying slimline windows?
Send opening sizes or drawings, window types, glass, colour and destination to sales@metline.in for a profile recommendation and delivered quotation.
