Search for a sliding casement window and the results will contradict each other. One page describes an ordinary horizontal slider that simply uses squarer, casement-like sash profiles. Another describes a sash that travels along a track and then also swings open on hinges. A third describes a sash that slides freely and then, in the last few centimetres of handle rotation, is pulled sideways onto continuous compression seals. All three are sold under the same name, and they do not perform the same way.
That ambiguity matters because the difference between them is not cosmetic. It decides how much air leaks past the sash, how much driving rain the sill has to cope with, how heavy the hardware has to be, and how the window behaves ten years after handover. Before comparing prices or finishes, settle which of the three you are actually being quoted.
| What the seller usually means | What the sash actually does | What you end up with |
|---|---|---|
| Slider with casement styling | Rollers carry the sash the whole way; it parks against brush or wool-pile strips. | A conventional sliding window. Convenient, but air and water performance is set by the brush line, not by a compressed gasket. |
| Slides and swings | The sash disengages from the track and pivots on a hinge set. | Two opening modes in one unit. Needs a far heavier hardware set, careful corner clearance, and more maintenance points. |
| Slides, then presses (side press / tilt and slide) | Rollers only carry the sash while it travels; the closing stroke moves it sideways onto continuous seals. | Sliding operation with sealing that behaves like a casement. The highest hardware content of the three, and the one most buyers mean when they ask for a sliding casement window. |
Only the third type is a genuine hybrid. It is also the one most often quoted as if it were the first, which is where most disappointed buyers get caught.
You do not need a catalogue to tell the three apart. Stand in front of a sample unit, or ask a supplier for a short video of a sash being closed, and run three checks.
The third check is the useful one on a drawing review, long before a sample exists. Ask for the hardware schedule by name: if the quotation lists a transmission box, a defined number of locking points, and a rated pulley load, you are buying the hybrid. If it lists only rollers and a crescent lock, you are not.
A casement sash seals well because it is clamped: a multi-point drive pulls it squarely onto compression gaskets all the way around. A sliding sash cannot be clamped in the same way, because it has to stay free to move. That is why the sliding category has historically leaned on brush strips, and why it has historically leaked more air.
Side-pressure hardware solves this by separating the two states. While the sash travels, rollers carry the weight and nothing is compressed. In the closing stroke, the drive takes over and moves the sash laterally, pressing it against a continuous seal line. The rollers effectively hand the load back to the seals. Nothing rubs while the window is moving, and nothing is left uncompressed while it is shut.
This is why the hardware, not the profile, is the item to interrogate. In ALPES’s TS130 side press window, the running and locking package is German ROTO side-pressure hardware with an eight-point locking system, carried on 200 kg load-bearing pulleys. The sealing is a four-sided continuous strip with sealant applied between the upper rail and the frame, plus the side-pressure rubber strip seal that gives the unit its casement-type closing behaviour. The sash runs at 75 mm wide with a 55 mm glass sash, inside a 130 mm frame with a 53/31 mm track height, on 6060-T66 profiles at 1.8–2.0 mm wall thickness with PA66GF25 thermal break strips.
Configuration matters too. The TS130 is offered as one fixed plus one movable, or as a middle-fixed panel with two movable panels on either side — in effect a triple sliding window layout, which is the arrangement most wide living-room openings end up needing. Buyers sourcing sliding tilt windows wholesale should confirm which of these two layouts the quoted hardware set supports, because the locking arrangement is not identical between them.
Because the name is ambiguous, the fastest way to pin a quotation down is to compare published geometry and hardware rather than descriptions. The table below sets out the ALPES sliding and side-press units alongside two compression-seal windows from the same range, so the trade-off is visible in numbers.
| Model | Frame / track | Sash and glass | Running gear and locking | How to read it |
|---|---|---|---|---|
| TS130 side press window | 130 mm frame; track height 53/31 mm | 75 mm sash; 55 mm glass sash | ROTO side-pressure hardware; eight-point locking; 200 kg pulleys | The true sliding casement. Quote this when the brief asks for sliding operation with casement-type sealing. |
| SL155 thermal break sliding door | Four-track 155 mm | 44.5 mm sash; 54.5 mm glass sash | Single-panel double-rail self-balancing pulley, 20 wheels, 400 kg capacity | Large-format work. Single sash up to 2800 x 2600 mm, opening area up to 7.5 sq m. |
| SL112/167 heavy-duty sliding door | 112 mm (single/two track); 167 mm (three track); 45 mm high-ｄｒｏｐ bottom track | 53/75 mm sash; 43 mm glass sash | Single sash driving capacity 220 kg; optional 85 mm water barrier | The weather-exposed option. Drainage and the water barrier are designed into the sill, not added on site. |
| SL126/182(75) thermal break sliding door | 126 mm two-track / 182 mm three-track; high track 43 mm, low track 8 mm | 75 mm sash; 55 mm glass sash | Multi-point locking, stainless steel locks in precision-cast reinforced casings; butyl gasket at frame-sash joints | The slim-interlock option, for when the 75 mm central sightline matters more than maximum panel size. Sliding or lift-sliding. |
| C120 outward opening casement | 119 mm frame; K-value 1.6 | 62 mm glass sash | ROTO transmission box; anti-pry lock points | The compression-seal benchmark. Anything sliding should be compared against this number, not against another slider. |
| AW90 passive / tilt and turn | 90 mm frame; K-value 1.3 | 90 mm glass sash | Winkhaus hardware; 360-degree locking point distribution; 240-hour salt spray; 5,000 N shear | The thermal and structural ceiling of the range. The honest reference point when a project is driven by U-value. |
Specifying on the strength of a name is how projects end up with the wrong unit. The decision is really about what the opening has to do.
The point of a written enquiry is to make two quotations comparable. These ten questions do that, and most of them take a supplier under an hour to answer.
| Ask | A good answer looks like | Red flag |
|---|---|---|
| Does the sash compress onto seals when closed? | A named mechanism, a named hardware brand, and a stated number of locking points. | “High sealing performance” with no mechanism behind it. |
| Hardware brand and model | ROTO, Winkhaus, CMECH or Wehag named on the quotation. | “German hardware” or “imported hardware” with no brand. |
| Rated pulley load versus actual sash weight | Both numbers given, with headroom between them. | Only the roller rating, or neither. |
| Alloy grade and measured wall thickness | 6060-T66, with 1.8–2.5 mm stated per profile. | “High-grade aluminium” with no temper or thickness. |
| Thermal break material | PA66GF25, with strip width stated. | “Thermal break” with no material named. |
| Calculated U-value for your exact size and glass | A figure tied to a specific configuration, with the glass build stated. | A single number quoted for every size in the range. |
| Water rating and test report | A standard named, plus a report you can read. | “Passed waterproof testing” with no reference. |
| Sill drainage and threshold detail | Track height, drain path, and whether a water barrier is available. | No section drawing of the sill. |
| How the sash is removed for service | A written sequence, plus the tools required. | “Our installer will handle it.” |
| Spare parts available with the first order | A priced list: rollers, gaskets, handles, locks. | No spares line on the quotation at all. |
Most of the complaints about sliding windows are not about the window. They are about the sill, and they show up two or three years in.
Sometimes, and that is the problem. Many sellers use the term for an ordinary brush-sealed slider with squarer sash profiles. The version worth specifying is the side-press type, where the sash is drawn onto continuous compression seals during the closing stroke. Ask which mechanism is being quoted.
An outward casement. It is clamped squarely onto gaskets by a multi-point drive, with no sliding clearance to design around. A side-press slider closes most of that gap and is dramatically better than a brush-sealed slider, but if your specification is chasing the lowest possible U-value, the casement range is still the reference point.
Yes. The TS130 is offered as a middle-fixed panel with a movable sash on each side, as well as the simpler one-fixed, one-movable arrangement. Confirm the locking arrangement for the three-panel version, because it is not the same hardware set as the two-panel one.
It depends on which system you are quoting. The SL155 sliding door takes a single sash to 2800 x 2600 mm on a 400 kg pulley set; the SL126/182 takes a single sash to 2.5 x 3.0 m. Large panels are a pulley and profile decision, not a preference, so give your sizes with the enquiry.
Start with the hardware. Brand, model, number of locking points and rated pulley load tell you almost everything about how the window will perform and how long it will last. Then confirm the alloy temper, wall thickness, thermal break material and the U-value for your exact configuration.
Aluminium handles coastal exposure well, but the hardware and fixings decide the outcome. ALPES tests the AW90 to 240-hour salt spray resistance and uses 304 stainless steel high-load hinges on the C116. For any coastal site, ask for the salt spray test report on the specific hardware set you are buying, and specify stainless fixings in writing.
A sliding casement window is not one product with one performance level. It is a name covering three mechanisms, and the way to tell them apart is to watch what the sash does in the last few centimetres of closing. If it only parks, you have bought a slider. If it presses onto continuous seals, you have bought the hybrid — and the hardware schedule, the alloy temper and the sill detail are the three documents that will tell you whether the one you were quoted is the one you wanted.
