A sliding window with an arched head is a horizontal slider whose top edge curves instead of running flat — a shallow eyebrow, a segment arch, or a half-round sitting above a rectangular body. The look is old-world: Mediterranean villas, Victorian restorations, churches and period homes all use the arch to turn a plain opening into a feature. The question buyers actually ask is narrower than the name suggests, because an arch sliding window is built two different ways, and only one of them slides on a curved track.
Most catalogs that show an arch top sliding window are really showing a mulled assembly: a fixed radius transom welded or coupled above a normal rectangular slider. The lower part slides; the arch above it is sealed glass that does not move. This is the honest, repeatable way to get the look, because the curved piece stays put and the operating hardware stays on a straight run. A smaller number of makers bend the actual head rail and build a true radius-head operating sash. That is possible, but it is the harder and more expensive path, and it is where most sealing surprises live.
| Build method | What moves | Curve sealed how | Best for |
|---|---|---|---|
| Arch transom + rectangular slider | Only the lower rectangle | Fixed radius, compression gasket | Period look, lower risk |
| True radius-head slider | The curved sash itself | Bent frame plus curved track | Pure arch, higher cost |
An arch is not a drawing, it is a bent profile. The radius is set by two numbers you must give the factory: the clear opening width and the rise (how far the curve climbs above the spring line). A shallow eyebrow and a tall half-round need different die sets and different glass, so "arch" without a rise is an incomplete spec. The curved top rail is bent from the same alloy family used for the rest of the frame, but bending tightens tolerance control — the curve is the first place a gasket can stretch or a corner can open. Glass is the expensive part: a curved insulated unit means a shaped lite, and most suppliers keep the curved portion as a single fixed light rather than a double-glazed slider to avoid shaping the whole unit.
ALPES publishes one sliding window family — the TS130 side-press sliding window — and it is a rectangular system: 6060-T66 aluminium at 1.8–2.0 mm wall, PA66GF25 multi-chamber thermal break, a 130 mm frame wall, 55 mm glass sash, 75 mm sash width, 26 mm frame face and 53/31 mm tracks, German ROTO side-pressure hardware, 200 kg rated pulleys and an eight-point lock with four-sided continuous sealing. That rectangular body is the natural lower half of an arch assembly. Radius heads, custom shapes and period transoms are handled as a custom engineering question per project — the published catalog does not list a stock arch SKU, and it should not be assumed. For the thermal number, be precise: the sliding family carries no published K-value, so any whole-window figure must come from a calculation tied to your glass build. The K=1.3 (AW90), K=1.6 (C120) and K=1.7 (C116) values in the ALPES range belong to the tilt-turn and casement families, not to the slider, and they do not transfer to an arch head.
| ALPES element | Value | Note for an arch build |
|---|---|---|
| Profile | 6060-T66, 1.8–2.0 mm | Basis for bent head rail |
| Thermal break | PA66GF25 multi-chamber | Runs through the rectangle |
| Frame wall | 130 mm | Depth the arch assembly must meet |
| Hardware | ROTO side-pressure, 200 kg pulleys | On the straight lower run |
| K-value | Not published for slider | Ask for project calc |
An arch head wins on character and on high transom daylight: a radius light above a slider throws soft morning sun deep into a room and reads as designed, not specified. It restores period homes where a flat head would look wrong. It costs on three fronts. Lead time: a bent profile and a shaped glass lite are made to order, not pulled from stock. Glass: a curved insulated unit is a premium part. Sealing: the curve is the longest uninterrupted gasket line in the unit, so it demands the tightest tolerance — and it is the hardest place to clean from inside. If your goal is the look without the risk, the arch-transom-over-rectangle route gives you most of the visual for a fraction of the effort.
| If you want | Choose | Trade-off |
|---|---|---|
| Period character, low risk | Arch transom plus rectangular slider | Arch does not open |
| Pure curved sash that slides | True radius-head slider | Cost, lead time, sealing care |
| Same daylight, simpler build | Keep rectangular TS130 | No arch feature |
Send the factory four things and the arch stops being a guessing game: the rectangle body width and height (for example a 48 x 36 sliding window or a 60 x 48 sliding window body), the rise or radius of the curve, the glass build for both the fixed arch and the sliding lite, and whether the lower part operates. A 72 x 48 sliding window body with a shallow eyebrow is a different die and a different gasket than a tall half-round, so the rise is not optional. Confirm the finish — Ice Cream White, Aurora Gray, Starry Sky Gray or Brown Coffee, with custom matching — on the bent rail, because a curve shows powder-coat uniformity more than a flat one does.
An arch sliding window is almost always an arched transom mulled above a rectangular slider, not a curved sash on a curved track. Build the rectangle on a proven system like the ALPES TS130, treat the arch as a custom-shaped fixed light, confirm the rise, and you get the period look without betting the whole seal on a bent profile. Ask for a project-specific K-value rather than borrowing one from the casement range, and the arch will perform as well as it photographs.
