Inward folding
Sashes stack inside, out of the rain and away from outdoor furniture, but over the worktop. Check that taps, shelves and appliances will not block the stack.
Window systems
Aluminium Bifold Windows
An aluminium bifold window is a set of hinged glazed sashes that fold and stack to the side, opening almost the full width of a window to the outside. It is the standard choice for kitchen pass-through windows, café and bar serveries and garden-room walls, where a counter replaces the doorway. Metline supplies bifold window profiles and thermally broken sections, with matching hardware, accessories and finishes, to window fabricators and project buyers worldwide.
- Sashes
- 2 to 6+ per run
- Frame
- 6063-T5 / T6, thermal break
- Glazing
- Double, triple, laminated
- Uses
- Kitchens, cafés, bars, terraces
What a bifold window is and why aluminium
A bifold window works like a bifold door set at counter height: the sashes are hinged to each other, carried on rollers in a top or bottom track, and fold into a compact stack at one or both sides of the frame. Fully open, the window leaves a clear opening of about 90 % of its width, with nothing in the way between inside and outside.
The appeal is practical as much as visual. A kitchen with a bifold window over the worktop can pass food and drinks straight to a terrace table; a café can serve takeaway customers without them entering; a bar can open its whole frontage to outdoor seating on a summer evening and close it again in minutes. Unlike a sliding window, which only ever opens half its width, a bifold opens almost all of it.
Aluminium is the natural frame material for these windows. Extruded 6063 sashes are strong enough to stay square under double or triple glazing at sash widths up to about 1 m, yet slim enough to keep sightlines narrow. The metal does not swell with kitchen steam or rain, so the hinges and rollers stay aligned, and powder-coated or anodised frames tolerate frequent cleaning, grease and outdoor exposure. Thermally broken profiles bring the window up to the energy standard of the rest of the building envelope.
Where aluminium bifold windows are used
| Application | Recommended layout | Points to confirm |
|---|---|---|
| Kitchen to terrace pass-through | 2 – 4 sashes folding to one side | Worktop height, sill detail over the counter, folding direction away from the hob or sink |
| Café or takeaway servery | 3 – 4 sashes, often outward folding | Frequency of use, hardware rated for high cycles, insect screen, lockable from inside |
| Restaurant frontage to outdoor seating | Multi-sash runs, split to both sides | Weather exposure, staff traffic, security when closed |
| Outdoor or poolside bar | 3 – 6 sashes over a bar top | Counter overhang, safety glass, corrosion-resistant hardware |
| Garden room, sunroom or veranda | Several runs around the room, sometimes corner layouts | Wind load, thermal performance, matching the doors |
| Hotels, villas and resorts | Large runs or corner bifolds | View, ventilation, coastal finish, matching colours across buildings |
| Small service hatch | Two sashes, or consider a top-hung or sliding hatch | Budget and how often it is opened |
In a typical domestic kitchen, the window sill sits on the worktop at about 900 – 950 mm above floor level, and the frame is set slightly in from the outside face of the wall so that the outdoor counter or shelf can line up with the indoor worktop. In commercial serveries, a sloping external sill or stainless-steel counter is common, with a drip to shed rain away from the frame.
Panel layouts and folding codes
Bifold windows are described by the number of sashes folding to each side and the direction of opening. The code tells the fabricator exactly how to build the window.
| Folding code | Meaning | Best for |
|---|---|---|
| 2L / 2R | Two sashes, both folding left or right | Small hatches and narrow kitchen openings |
| 3L / 3R | Three sashes to one side | Compact pass-throughs and small bar windows |
| 4L / 4R | Four sashes to one side | Medium patio windows and restaurant serveries |
| 5L, 6L and above | Larger single stacks | Café frontages and villa terraces |
| 2L1R, 3L1R, 1L3R | Unequal split, one sash or a few on the short side | Openings where a wall, cupboard or tap restricts one side |
| 2L2R, 3L3R | Equal split from the centre | Wide openings needing symmetry and central service |
| Corner layouts | Two runs meeting with no fixed post | Corner bars and panoramic garden rooms |
Outward folding
Sashes stack outside, leaving the worktop free. Wind pushes the sashes onto their gaskets, which improves weather performance. Check that the stack will not obstruct a path.
Top-hung vs bottom-rolling
Windows are lighter than doors, so both work. Bottom-rolling keeps the head simple; top-hung keeps the sill clean for a counter.
Typical sash widths are about 450 – 900 mm, and window heights from about 600 mm to 1,500 mm or more. Fewer, wider sashes give a cleaner look; more, narrower sashes give a smaller stack. The best layout depends on the opening width, the counter position, the space on each side and how often the window is opened fully.
Profiles, thermal breaks and construction details
Typical bifold window system data
- Profile alloy
- 6063-T5 or 6063-T6 (EN AW-6063), 6060-T66 in some European systems
- Frame depth
- About 60 – 80 mm for double glazing, 90 mm and above for triple
- Wall thickness
- Typically 1.4 – 2.0 mm, thicker at hinge and roller fixings
- Thermal break
- Glass-fibre reinforced polyamide (PA66 GF25) strips, typically 20 – 34 mm
- Glass thickness accepted
- About 24 – 50 mm IGU, depending on series
- Corner joints
- Crimped or pinned corner cleats with structural adhesive
- Seals
- EPDM gaskets in frame, sash and interlocks
- Drainage
- Concealed drainage paths in the sill, with external outlets or covers
- Reinforced corners: sashes are opened many times a day in commercial use, so the corner joints must stay square under glass weight and handling.
- Multi-chamber sections: add stiffness and lengthen the heat path through the frame.
- Precision extrusion: tolerances to EN 12020-2 keep gasket compression even along the full sash, which is what actually seals the window.
- Concealed drainage: directs rain that passes the outer seal back outside without visible slots on the counter side.
Non-thermal frames are suitable for interior hatches and for open-sided structures such as pool bars in warm climates. Any window in a heated or air-conditioned building envelope should use a thermally broken system, or the frame will lose heat, gather condensation and fall short of energy-code limits.
Glazing for bifold windows
| Glazing option | Typical build-up | Suitable for |
|---|---|---|
| Toughened single glass | 6 – 8 mm | Interior hatches and open-air bars |
| Double-glazed IGU | for example 5 + 12A + 5 mm or 4 + 16Ar + 4 mm, Low-E, warm edge | Most homes, kitchens and cafés |
| Laminated IGU | Laminated inner or outer pane | Security, safety at counter height, noise reduction |
| Triple-glazed IGU | for example 4 + 12A + 4 + 12A + 4 mm with two Low-E coatings | Cold climates and low-energy buildings |
| Solar-control Low-E | Selective coating facing the cavity | Sun-facing serveries and hot climates |
| Tinted, frosted, patterned | Decorative pane within the IGU | Privacy, branding, back-of-house areas |
| Fire-resistant or security glass | Project specific | Commercial premises where codes require it |
Because bifold windows usually sit above a counter, glass at low level may count as a critical location under safety-glazing rules (for example BS 6262-4 in the UK or the safety-glazing provisions of the building code elsewhere), so toughened or laminated glass is normally specified. Glass weight also matters for the hardware: a 700 × 1,200 mm sash with a 4 + 16 + 4 mm unit carries about 17 kg of glass, which is comfortable for most systems, but triple glazing nearly doubles it.
Hardware, locking and insect screens
Hinges
Stainless-steel or aluminium hinges sized for sash weight; adjustable versions make fine alignment easy after installation.
Rollers and guides
Stainless or polymer rollers with sealed bearings. Commercial serveries benefit from high-cycle rated carriers.
Handles
Lever handle on the lead sash, flush handles or pulls on the others, so nothing catches on the counter.
Locks
Multi-point locking into head and sill, shoot bolts on intermediate sashes, and key locking for unattended premises.
Stays and restraints
Holders keep the folded stack from swinging in wind, important for outward-folding windows.
Insect screens
Pleated or retractable roller screens in fibreglass or stainless mesh, in a colour-matched frame, which slide clear of the stack.
Hardware is where most long-term problems start, so for kitchens, cafés and bars that open the window many times a day, specify hardware tested for repeated opening and closing (EN 1191 cycle testing or the system supplier's equivalent) and in stainless steel or marine-grade finishes where there is salt air or cleaning chemicals.
Surface finishes and colours
| Finish | Typical standard | Typical film thickness | Best for |
|---|---|---|---|
| Polyester powder coating | EN 12206-1, Qualicoat class 1, AAMA 2603 / 2604 | 60 – 80 µm | Homes and general projects; any RAL colour, matt to gloss |
| Super-durable powder | Qualicoat class 2, AAMA 2604 | 60 – 80 µm | High UV and long colour-retention targets |
| PVDF (fluoropolymer) coating | AAMA 2605, Qualicoat class 3 | about 25 – 40 µm (2 – 3 coats) | Coastal sites, high-rise facades, long warranties |
| Anodising | EN ISO 7599, Qualanod, AAMA 611 | 15 – 25 µm (class 15 – 25) | Metallic silver, bronze, champagne and black |
| Wood-grain transfer | Sublimation over powder base coat | as base powder | Timber look with aluminium durability |
| Dual colour | Different powder inside and out, split at the thermal break | 60 – 80 µm | Exterior to match the facade, interior to match the room |
Powder coating in any RAL colour is the usual choice for homes and cafés. PVDF suits coastal and high-UV sites, and anodising gives a durable metallic finish for commercial frontages. Wood-grain finishes give the look of timber without the maintenance, and dual-colour frames can match the facade outside and the kitchen inside. Architects can specify finishes to Qualicoat, Qualanod or AAMA requirements, and project orders should approve a colour sample and gloss level before production.
Performance, testing and standards
| Property | Standard | What to ask for |
|---|---|---|
| Air permeability | EN 12207 / EN 1026; ASTM E283 | Class 3 – 4 for envelope windows |
| Watertightness | EN 12208 / EN 1027; ASTM E547 | Class appropriate to exposure; lower with flush sills |
| Wind-load resistance | EN 12210 / EN 12211; ASTM E330 | Class matched to building height and location |
| Thermal transmittance | EN ISO 10077-1/-2; NFRC 100 | Uw for the actual size and glass; typically 1.2 – 1.8 W/m²K with double glazing |
| Acoustic insulation | EN ISO 10140 / EN ISO 717-1 | Rw with the chosen glass, important near roads |
| Durability of operation | EN 1191, EN 13115 | Cycle and operating-force results for high-use serveries |
| Security | PAS 24 (UK), EN 1627 | Tested evidence for ground-floor and commercial windows |
In Europe, bifold windows placed on the market carry CE or UKCA marking under EN 14351-1 with a declaration of performance. In North America, operable windows are rated under NAFS (AAMA/WDMA/CSA 101/I.S.2/A440). Ask for test reports on the specific system and size range, because results depend on sash size, folding direction and sill type.
Bifold window or sliding window?
| Requirement | Aluminium bifold window | Aluminium sliding window |
|---|---|---|
| Opening area | About 90 % of the width | About half the width |
| Pass-through and service use | Excellent: nothing in the opening | Possible, but through a narrower gap |
| Indoor-outdoor connection | Strong; the wall effectively disappears | Limited |
| Cost | Higher: more sashes, hinges and rollers | Lower and simpler |
| Daily operation | Smooth if well installed; more moving parts | Very simple |
| Sealing and maintenance | More joints; keep tracks and drainage clean | Fewer joints; easy upkeep |
| Best for | Kitchens, serveries, bars, terraces, garden rooms | Standard windows, ventilation, tight budgets |
A top-hung (awning) hatch or a vertical sliding servery window is a sensible alternative for very small openings or tight budgets. Where you want the whole opening clear, the bifold remains the best option.
Installation, maintenance and common mistakes
A bifold window is only as good as its installation. Because several sashes hang from one set of tracks, a frame that is out of square or a sill that is not level by more than a millimetre or two makes the sashes bind, drop or leak. The frame should be fixed to a sound, level structural opening, packed under every fixing point, and sealed to the wall with a compatible membrane or tape and sealant on the outside and an airtight seal on the inside.
- Mistake: ignoring the stack. Folded sashes project from the frame by roughly their own width. Check they will not hit a tap, wall cabinet, light fitting or outdoor heater.
- Mistake: too many narrow sashes. Each extra sash adds a sightline, hinges and rollers. Two or three wider sashes are often cleaner and cheaper than five narrow ones.
- Mistake: no drainage plan. Over a counter, rain that passes the outer seal must drain outside, not onto the worktop. Use a drained sill and an external drip.
- Mistake: under-rated hardware. Commercial serveries open many times a day; residential-grade rollers wear quickly in that duty.
- Mistake: non-safety glass at counter height. Glass close to a worktop or floor is usually a critical location requiring toughened or laminated glass.
Maintenance is simple but should be regular. Vacuum and wipe the tracks and drainage outlets every few months, more often in a busy café or on a dusty site. Clean powder-coated and anodised frames with mild detergent and water, never abrasive pads or solvents. Lubricate locking points once or twice a year with a non-greasy lubricant, and check hinge adjustment if a sash starts to rub. On coastal sites, rinse frames and hardware with fresh water to remove salt, which keeps both the finish and the stainless-steel parts looking new for longer.
How to specify and order
- Opening detailsRough opening width and height, wall depth, counter or sill height, and the position of taps, shelves or appliances near the window.
- LayoutFolding code (e.g. 3L, 2L2R), inward or outward folding, and whether a single sash should open independently as a vent.
- PerformanceThermal, acoustic, wind-load and security requirements, and the local standard the window must meet.
- Finish and extrasColour inside and out, glazing build-up, screens, hardware finish, and any glazing bars.
- Quote and deliveryWe return a profile list and quotation on EXW, FOB, CIF or DAP terms; profiles and hardware ship film-protected and crated, labelled by opening.
References and standards
- EN 14351-1 – Windows and doors: product standard, performance characteristics
- EN 12207 / EN 12208 / EN 12210 – Air permeability, watertightness and wind-load resistance classification
- AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS) – North American Fenestration Standard for windows, doors and skylights
- EN 12020-2 – Extruded precision profiles in alloys EN AW-6060 and EN AW-6063: tolerances
- BS 6262-4 – Glazing for buildings: safety related to human impact
Aluminium (aluminum) bifold windows: FAQ
How wide can an aluminium bifold window be?
Runs of 4 – 6 m are common and longer runs are possible by splitting the sashes to both sides. Individual sashes are usually 450 – 900 mm wide.
What height should a kitchen bifold window be?
Usually the sill sits on the worktop at about 900 – 950 mm above the floor, with the head aligned to doors or other windows. Window heights of about 1,000 – 1,200 mm are typical for kitchens.
Should a bifold window fold inward or outward?
Outward folding keeps the worktop clear and seals better under wind; inward folding keeps the sashes out of the weather and off the terrace. Check what is in the way on each side before deciding.
Are aluminium bifold windows energy efficient?
With a thermally broken frame and a Low-E double or triple glazed unit, whole-window U-values of about 1.0 – 1.8 W/m²K are achievable, depending on size and glass.
Can insect screens be fitted to bifold windows?
Yes. Pleated or retractable roller screens slide across the opening and park clear of the folded sashes, which suits kitchens and cafés.
Which aluminium alloy is used for bifold window profiles?
6063 in T5 or T6 temper (6060 in some European systems), extruded to precision tolerances and finished with powder coating, PVDF or anodising.
Planning a bifold servery or kitchen window?
Send the opening size, counter height, folding layout and finish. We will propose a profile series and quote profiles and hardware delivered to your site.
