Sash horns
Small projections below the top sash stiles, originally added to strengthen joints in timber sashes. Aluminium systems offer clip-on or integral horns for period façades.
Vertical sliding windows
Aluminium Sash Windows
An aluminium sash window has one or two glazed sashes that slide up and down within the frame, balanced by springs so they stay where they are left. Built from thermally broken 6063 extrusions, it keeps the proportions of a traditional sash window while cutting maintenance and improving insulation. Metline supplies single hung, double hung and vertical sliding sash window profiles, thermal-break sections and balances to window fabricators for renovation and new-build projects worldwide.
- Types
- Single hung, double hung, vertical slider
- Profile alloy
- 6063-T5 / T6
- Thermal break
- 14.8 – 24 mm polyamide
- Glazing
- Double or triple Low-E IGU
What is an aluminium sash window?
The sash window is one of the oldest opening-window designs: two framed panes (sashes) in a box frame, at least one of which slides vertically. Traditional timber versions used cords, pulleys and cast-iron weights hidden in the frame. Modern aluminium versions replace the weights with compact spring balances in the jamb, which allows a slimmer frame.
Because a sash slides within its own plane, it never swings into a room or out over a walkway. That makes sash windows a good fit for narrow rooms, for windows facing balconies or pavements, and for tall, narrow openings where a casement sash would be heavy and awkward. Opening the top and bottom sashes together also sets up natural stack ventilation: warm air leaves at the top while cooler air enters at the bottom.
Aluminium suits the format well. Extrusions can be shaped with deep, slim meeting rails, integral horns and glazing beads that echo timber mouldings, and a durable powder coat or wood-grain finish removes the need for the repainting and repair that timber sashes demand.
Single hung, double hung and vertical sliding sash
| Type | How it works | Best for |
|---|---|---|
| Single hung | Top sash fixed, bottom sash slides up | Volume housing and projects where cost and simple hardware matter |
| Double hung | Both sashes slide; often tilt inwards for cleaning | Upper floors, better ventilation control, easy cleaning from inside |
| Vertical sliding sash (UK) | Double hung styled as a traditional box sash, with horns and slim meeting rail | Renovation, period façades and conservation settings |
| Triple or tall sash | Three sashes in a tall frame, or a tall bottom sash | Very tall openings such as walk-out bays |
Single hung windows have fewer moving parts and a fixed top sash that seals well, so they are cheaper and slightly more airtight. Double hung windows give flexible ventilation and, with tilt-in sashes, let occupants clean both sides of the glass from inside, which is the deciding factor for apartments and upper floors. For a deeper look at the double hung format, see aluminium double hung windows.
Frame, profile and thermal break configuration
Typical system configuration
- Profile alloy
- 6063-T5 or 6063-T6 extrusion to EN 755 / ASTM B221
- Profile wall thickness
- Typically 1.4 – 2.0 mm on main members, heavier on meeting rails of large sashes
- Structure
- Thermally broken or non-thermal profiles, depending on climate and energy target
- Thermal break
- Glass-fibre reinforced polyamide strips, typically 14.8, 18.6 or 24 mm
- System depth
- Deep box-frame systems (around 116 – 197 mm) for traditional proportions
- Sightlines
- Slim frames, with sash width adjusted to suit the façade
- Sizes
- Made to the window schedule and opening survey
The thermal break is the single biggest factor in the frame's insulation. Aluminium conducts heat several hundred times better than polyamide, so separating the inner and outer extrusions with polyamide strips stops the frame acting as a cold bridge. Wider strips and foam-filled cavities lower the frame U-value further. In cold climates, unbroken aluminium frames are prone to condensation on the inner face and rarely meet energy codes.
The 6063 alloy is used because it extrudes cleanly into thin, complex hollow sections with a fine surface for coating, and its T5 or T6 temper gives enough stiffness for sash frames. See our 6063 extrusions page for chemistry and properties.
Performance targets and the standards behind them
Window performance is declared in the class system of the project country. The same window can be tested to more than one system, so state the standard and class you need in the enquiry.
| Property | Europe (EN 14351-1) | North America | Australia | Typical target for aluminium sash |
|---|---|---|---|---|
| Air permeability | EN 12207, classes 1 – 4 | NAFS (AAMA/WDMA/CSA 101/I.S.2/A440) | AS 2047 | EN class 3 – 4 |
| Water tightness | EN 12208, classes 1A – 9A and E | NAFS water test pressure | AS 2047 | Class 7A – 9A or better |
| Wind resistance | EN 12210, classes 1 – 5 and A – C | NAFS performance grade (design pressure) | AS 2047 / AS 1170.2 wind region | Up to about 2000 Pa test pressure |
| Thermal transmittance | Uw to EN ISO 10077 | NFRC 100 U-factor | WERS ratings | Uw about 1.4 – 1.8 W/m²·K |
| Acoustic | Rw to EN ISO 717-1 | STC / OITC | Rw | Rw 32 – 38 dB with laminated glass |
Targets are typical ranges for thermally broken aluminium sash windows with double Low-E glazing; actual results depend on size, glazing and testing. Building regulations set legal limits, for example a maximum U-value of 1.4 W/m²·K for replacement windows in existing dwellings in England (Approved Document L).
Keeping a traditional sash appearance
Georgian bars
Glazing bars that divide each sash into smaller panes. Bars bonded to both faces of the glass with a spacer bar between give the look of true divided panes with full insulated glazing.
Slim meeting rail
The horizontal rail where the two sashes meet. A slim, deep rail is the key detail that makes an aluminium sash look like timber.
Heritage colours
Off-whites, greys, greens and black in matt or satin finishes match traditional painted joinery.
Wood-effect finish
Wood-grain transfer gives a timber appearance inside or out without timber maintenance.
Proportions
Frame and sash widths are adjusted to the original opening proportions, which matters in conservation areas.
In conservation areas and on listed buildings, replacing timber sashes with any other material may need consent. Many planning authorities will consider aluminium where the sightlines, glazing bars and meeting rail match the original closely, so detailed drawings and a sample are worth preparing before applying.
Glazing and balance systems
| Glazing option | What it does | Typical use |
|---|---|---|
| Double Low-E IGU, argon filled, warm-edge spacer | Lowers heat loss; standard for energy-efficient windows | Most housing |
| Triple IGU | Further reduces heat loss; heavier sashes | Cold climates, passive designs |
| Toughened (tempered) glass | Safety glazing that breaks into small pieces | Low-level panes and areas near doors |
| Laminated glass | Holds together when broken; improves security and sound insulation | Ground floors, schools, upper floors |
| Acoustic laminated glass | Special interlayer damps sound | Roadside, rail and airport-noise sites |
Glass weight drives the balance choice. A double-glazed sash of 1 m × 0.8 m with two 4 mm panes weighs about 16 kg for the glass alone; triple or laminated glazing can make it half as heavy again. The balance must be rated for the full sash weight or the sash will drift down or be hard to lift.
Spiral balances
A twisted rod inside a tube in each jamb. Compact and economical for light to medium sashes.
Block-and-tackle balances
A spring and pulley set in a channel; carries heavier sashes and allows tilt-in operation.
Constant-force coil springs
Flat coiled springs give the same support at any height; good for heavy or tall sashes.
Locks and restrictors
Cam or sash locks on the meeting rail, plus ventilation stops or restrictors on upper floors and in schools.
Where aluminium sash windows are used
- Renovation and period façades: replacing tired timber sashes while keeping horns, bars and proportions.
- Apartments and villas: tilt-in double hung windows that occupants can clean from inside.
- Upper floors and high-rise housing: no outward swing over walkways, with restrictors for child safety.
- Hotels, schools and public buildings: controlled ventilation openings and laminated or acoustic glazing.
- Coastal and exposed sites: marine-grade pre-treatment, PVDF or anodised finishes and stainless hardware.
Aluminium, timber and uPVC sash windows compared
| Factor | Aluminium | Timber | uPVC |
|---|---|---|---|
| Sightlines | Slimmest | Slim | Bulkiest |
| Maintenance | Washing | Repainting and repairs | Washing |
| Colour stability | Excellent with powder coat or PVDF | Needs repainting | Can fade or yellow |
| Thermal performance | Good with thermal break | Good | Good |
| Authentic heritage look | Good with slim rails and horns | Best | Fair |
| Relative cost | Medium to high | High | Low to medium |
If a project needs a larger clear opening or the tightest compression seal, a casement window may be a better choice; wide horizontal openings suit sliding windows, and openings that only need light and views can use fixed windows.
From window schedule to delivery
- Confirm types and scheduleSingle hung, double hung or vertical slider for each opening, with sizes from the survey or drawings.
- Match glass and balancesGlass build-up and sash weight checked against the balance rating.
- Fix proportionsFrame and sash sightlines, meeting rail, horns and bars confirmed on drawings.
- Review sealing and installationDrainage, sill details, fixing method and the wall build-up.
- Check finish and hardwareColour, coating standard and hardware consistent across batches.
- Inspect and labelProfiles checked and labelled by window number, floor or zone, then packed for export on EXW, FOB, CIF or DAP terms.
For your enquiry, include the window types, schedule or photos of existing windows, performance targets, glazing, hardware preferences, finish and colour, site conditions and the destination port.
References and standards
- EN 14351-1 – Windows and doors: product standard, performance characteristics
- AAMA/WDMA/CSA 101/I.S.2/A440 – North American Fenestration Standard (NAFS)
- AS 2047 – Windows and external glazed doors in buildings
- NFRC 100 – Procedure for Determining Fenestration Product U-factors
- UK Government – Approved Document L: Conservation of fuel and power
- EN 755-2 – Aluminium and aluminium alloys: extruded profiles, mechanical properties
Aluminium (aluminum) sash windows: FAQ
What is the difference between single hung and double hung windows?
In a single hung window only the bottom sash moves; in a double hung window both sashes slide, and they often tilt inwards for cleaning. Single hung is simpler and cheaper; double hung gives better ventilation control and easier cleaning on upper floors.
How do sash windows differ from horizontal sliding windows?
Sash windows slide vertically and suit tall openings and traditional proportions. Horizontal sliders move left and right and suit wide, low openings.
Can aluminium sash windows use Low-E or acoustic glass?
Yes. Double or triple Low-E units, toughened, laminated and acoustic laminated glass can all be used. The heavier the glass, the stronger the balance system must be, so glass weight is checked against the balance rating.
Are aluminium sash windows energy efficient?
With a polyamide thermal break, warm-edge spacers and Low-E glazing, typical whole-window U-values are about 1.4 – 1.8 W/m²·K, enough to meet many building codes for replacement windows. Non-thermal frames are only suitable for mild climates.
Can aluminium sash windows replace timber sashes in a conservation area?
Often, if they match the original sightlines, meeting rail, horns and glazing bars closely. Consent rules vary, so prepare drawings and a sample for the planning authority.
What balance system do aluminium sash windows use?
Spiral balances for light sashes, block-and-tackle balances for heavier and tilt-in sashes, and constant-force coil springs for very heavy or tall sashes.
Specifying sash windows?
Send the window schedule, glazing, performance targets, finish and destination. We will reply with a profile proposal and a delivered price.
