Standard double-hung
Non-insulated or basic frames for warm climates, volume housing and replacement work where cost matters most.
Vertical sliding windows
Aluminium Double-Hung Windows
A double-hung window has two sashes that both slide vertically, held in any position by concealed balances, so it ventilates from the top, the bottom or both without projecting into the room or onto the facade. Tilt-in sashes let the outside glass be cleaned from indoors. Metline supplies double-hung window profiles, thermal break sections and hardware to window fabricators and project buyers worldwide.
- Operation
- Two vertical sliding sashes
- Alloy
- 6063-T5 / T6
- Balances
- Spiral, block-and-tackle, coil
- Rating
- NAFS H-R to H-AW
How a double-hung window works
Both sashes run in tracks in the frame jambs. Springs or balances hidden in the jambs counter the weight of each sash so it stays where it is left. When closed, the two sashes overlap at the meeting rail, where an interlock and a sash lock pull them together to seal.
Opening the top and bottom sashes together creates natural stack ventilation: warm air leaves through the top, cooler air enters at the bottom. Because nothing swings out, double-hung windows suit walkways, balconies and rooms where furniture sits close to the wall. They are the traditional window of North American housing and a close relative of the British sash window. A single-hung window looks the same but has a fixed upper sash, which costs less and seals slightly better.
The trade-off is air tightness. Sliding sashes rely on weatherstripping that the sash moves against, rather than gaskets squeezed shut, so double-hung windows are typically less airtight than casements of similar quality. Good aluminium designs reduce the gap with interlocking meeting rails, fin-seal pile weatherstrip and compression seals at the head and sill.
Double-hung window types
Thermal break double-hung
Polyamide-broken frames and sashes with Low-E insulated glass for cold and hot climates and energy codes.
Tilt-in double-hung
Sashes release from the tracks and tilt inward for cleaning, ideal above ground floor in apartments and hotels.
Commercial-grade
Heavier sections, stronger balances and opening limiters for schools, offices and hospitals, rated to CW or AW performance classes.
Single-hung
Fixed top sash and operable bottom sash; economical and common in multi-family housing.
Combinations
Double-hung units mulled with fixed lights, transoms or side units to fill large openings.
Frames, balances, glass and hardware
| Component | Options | Notes |
|---|---|---|
| Frame and sash profiles | 6063-T5 or T6 extrusions, walls about 1.2 – 2.0 mm; thermal break optional | Deeper sections for larger sashes and higher wind ratings |
| Balances | Spiral (tube) balances, block-and-tackle, constant-force coil springs | Sized to sash weight; heavier triple glazing needs stronger balances |
| Meeting rail | Interlocking rails with weatherstrip and cam lock | Main seal and security point |
| Glazing | Double or triple insulated glass, Low-E, argon, laminated or acoustic | Glass weight drives balance choice |
| Safety hardware | Opening limiters, window opening control devices, tilt latches | Required on upper floors in many codes |
| Grilles and screens | Grilles between glass or simulated divided lites; half or full insect screens | Traditional look and ventilation |
| Finish | Powder coating to AAMA 2603/2604/2605, PVDF, anodising, wood-grain | Dual colour on thermally broken units |
Performance ratings and safety rules
In North America double-hung windows are rated to AAMA/WDMA/CSA 101/I.S.2/A440 with the product code "H" followed by the performance class and grade, for example H-LC50 or H-CW60. Energy ratings come from NFRC 100 and 200. In Europe, vertical sliders fall under EN 14351-1 with air, water and wind classes from EN 12207, EN 12208 and EN 12210.
- Fall protection: the US IRC requires window opening control devices (ASTM F2090) or a fixed limit where the sill is less than 24 in (610 mm) above the floor and the window is more than 72 in (1829 mm) above outside grade.
- Emergency escape: bedroom windows used for egress need a net clear opening of at least 5.7 ft² (0.53 m²), 5.0 ft² at grade floor, with minimum 24 in height and 20 in width and a sill no higher than 44 in. Because only one sash opens, double-hung units must be sized generously to comply.
- Safety glazing: required near doors, low sills and in wet areas under local codes.
Where double-hung windows work best
- Residential towers and housing: bedrooms, living rooms and kitchens where windows must not project.
- Hotels and serviced apartments: tilt-in sashes and limiters for safe operation and cleaning.
- Schools and dormitories: commercial-grade units with restricted openings.
- Renovation: replacing old timber or steel hung windows with matching proportions.
- Offices and hospitals: mid-rise buildings needing controlled natural ventilation.
For better air tightness, compare casement windows; for a British heritage look, see sash windows.
References and standards
- AAMA/WDMA/CSA 101/I.S.2/A440 – North American Fenestration Standard
- ASTM F2090 – Window fall prevention devices with emergency escape release mechanisms
- International Residential Code R310 and R312 – Emergency escape openings and window fall protection
- EN 14351-1 – Windows and doors: product standard, performance characteristics
- NFRC 100 – Procedure for determining fenestration product U-factors
Aluminium (aluminum) double-hung windows: frequently asked questions
What is the difference between single-hung and double-hung windows?
In a double-hung window both sashes slide; in a single-hung window only the lower sash moves and the upper one is fixed. Double-hung gives more ventilation options and easier cleaning; single-hung costs less.
Are double-hung windows energy efficient?
They can be, with thermal break frames, Low-E insulated glass and good weatherstripping, but they are usually slightly less airtight than casement windows because their seals slide rather than compress.
Can aluminum double-hung windows meet egress requirements?
Yes, if sized so the single opening sash gives at least 5.7 ft² of clear opening with minimum 24 in height and 20 in width. This often means a taller or wider unit than a casement would need.
What balance type should I choose?
Spiral balances suit light to medium sashes; block-and-tackle and constant-force coil balances handle heavier sashes and triple glazing. The balance must match the sash weight for smooth operation.
Do you supply double-hung window profiles for local fabrication?
Yes. Metline supplies frame and sash profiles, thermal break sections and hardware in mill, anodised or coated finishes; we do not supply complete windows, which your fabricator assembles.
Need double-hung windows?
Send the window schedule, ratings and finish. We will quote profiles and hardware delivered to site.
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