ALPES builds aluminium system windows, and the casement is the core of that range. Three series carry the name — the C113, the C116 and the C120 — and every one of them opens outward. The fourth window in the catalogue, the AW90, opens inward. Buyers tend to file that away as a stylistic difference, the way they file away a colour choice. It is not one. The direction a sash swings decides where your insect screen has to live, how large a single sash can physically be, what a gust of wind does to the window, where rainwater has to go, who is going to clean the outside glass, and what you are allowed to mount in the opening. Six consequences, all set by one line on the drawing.
We have written elsewhere about reading sightlines on a slim casement, and about putting the C113 and the C116 side by side. This piece starts where those two stopped. It is not a product tour; it is the set of questions you should be able to answer before any of the four series is the right one for your building.
Most enquiries arrive with a series name already in mind. That is the wrong place to start, because direction filters the field faster than anything else on a specification sheet. An outward-opening sash is pushed away from the building. Closed, that is a genuine structural advantage: wind pressure presses the sash onto the frame and onto the compression seals, so the harder it blows, the tighter the window gets. European window guides describe exactly this, noting that an outward sash is very tight when closed because the wind pushes it harder towards the frame. Open, the same sash becomes a sail. Every kilogram of glass is now hanging on the stay, levered outward, and the load path runs through four fixings into the profile. Nothing about the extrusion changes; everything about the loads does.
| Condition | Outward casement, sash closed | Outward casement, sash open |
|---|---|---|
| Wind | Pressure drives the sash into the frame; the seals work harder, not less | The sash is a sail; the load reverses onto the stay and its fixings |
| Rain | Water runs down the outer face and away from the inner seal | Water reaches the sash edge and the open joint |
| Inside the room | Sill and floor stay clear; curtains and blinds are never disturbed | Still clear — this is the outward casement's lasting advantage |
| Outside the wall | Nothing protrudes | The sash occupies a full arc outside the wall; cleaning happens out there |
Where this points is simple. If your building is low, sheltered, and has safe external access, an outward casement is the most efficient opening you can buy: it gives you the whole aperture, it keeps the room clear, and it seals harder in a storm. If it is tall, exposed, or has no safe way to reach the outer glass, the same window becomes a decision with consequences — and in some jurisdictions it is not available to you at all.
An outward sash cannot have a screen on the outside of it. The screen therefore has to sit inboard, and that single fact produces four consequences that buyers rarely price in.
The same geometry shapes almost every casement window treatment ideas question people arrive with. Inboard roller blinds, curtains, interior shutters and plantation shutters all work beautifully, because the sash never enters the room to hit them. External shutters and external roller blinds are the casualties. The one treatment that needs care is a blind mounted on the sash itself: it travels with the sash, adds weight to the stay, and therefore belongs in the same calculation as the glass.
Because the screen is unavoidable on an outward casement, the ALPES series treat it as part of the assembly rather than an add-on. The C120 is built as an integrated door and window unit, with the frame, sash and screen sealed together using injection-moulded structural adhesive and a nail-free rolled-press screen structure, finished with a seamless threshold; 40# black stainless steel mesh is standard, with anti-PM2.5 and 80# options. The C116 brings the glass sash and the screen flush with each other on a 14 mm interior profile, with 80# black or grey stainless mesh or anti-PM2.5 mesh. The C113 ships with a black high-definition anti-PM2.5 mesh. The AW90 carries 40# black stainless mesh as standard with anti-PM2.5 as an option — and because it opens inward, its screen can go on the outside of the building, which is the whole point of the next section.
Ask a factory for the largest casement sash it can build and you will usually be given a number derived from the profile. That number is close to meaningless. The part that gives out first is not the extrusion — it is the friction stay, the scissor arm that carries the sash, holds it at an angle and resists wind. Published ratings from the hardware makers themselves are the only honest ceiling, and they are far lower than most buyers expect.
| Published hardware rating | Application | Max sash width | Max sash height | Max sash weight |
|---|---|---|---|---|
| 22 mm groove stainless stay, size 10 | Side-hung and top-hung | 500 mm | 1100 mm | 23 kg |
| Same family, size 14 | Side-hung and top-hung | 600 mm | 1300 mm | 29 kg |
| Same family, size 18 | Side-hung and top-hung | 700 mm | 1500 mm | 35 kg |
| Ferritic stainless stay, 16 inch | Side-hung, 13 and 17 mm stack heights | 700 mm | 1350 mm | 24 kg |
| Heavy-duty egress easy-clean stay | Egress side-hung | 1000 mm | Not stated alongside | 50 kg |
Read that table for the shape of the limit rather than the exact figures, which vary by maker and by groove. The shape is the point: on a side-hung sash the width is the tight dimension, and it is the one everybody assumes is generous. Widths top out well below the matching heights. A Foshan aluminium profile supplier arrives at the same place from the other side of the industry, advising that an outward casement sash stay below about 650 mm in width. Treat that as one published opinion rather than a rule, but notice that it lands in the same band as the hardware tables above.
Now put glass on it. Glass weighs roughly 2.5 kg per square metre for every millimetre of thickness, and that figure counts glass only — the sash profile and the hardware come on top. A 6+12A+6 insulated unit contains 12 mm of glass in total, so about 30 kg per square metre. Take a 36 x 36 casement window, which is roughly 914 mm square or 0.84 square metres: the glass alone is about 25 kg, before a single millimetre of aluminium. Add the sash and you have already passed the smallest stay in the table.
This is why "what is the biggest sash you make" is the wrong question. The right one is: what is the maximum sash width and height for this series, at this glass build-up, with this stay. Ask all three together, because each one moves the other two. ALPES publishes frame widths, glass sash thicknesses and mullion dimensions for every casement series, but it does not publish a maximum sash size for any of them. That is a gap to be closed with a written answer on your own opening, not with a guess.
Closed, an outward casement gets better as the weather worsens. Open, it is the one window type where the weather can work against the hardware rather than for it. Two mechanisms sit between an open sash and a gust: the friction brake in the stay, which is what holds the sash at the angle you left it, and any restrictor that limits how far it can travel. Both are wear items, and the brake is the part that quietly stops doing its job. A sash that drifts closed in the wind, or slams, is usually telling you about the brake rather than the profile.
There is also a regulatory layer that no factory can answer for you. In China, outward-opening casements are widely cited as being restricted on high-rise buildings and prohibited on buildings above 100 m, with sliding sashes required to carry anti-fall devices; similar height-based rules exist in other markets. We publish this so that you take it to your local authority, not so that you take our word for it — we cannot certify a jurisdiction we do not build in. Where an outward sash is permitted, the engineering answers are unglamorous and worth asking for by name: an opening restrictor, and a secondary restraint. The C120 ships with a fall rope safety mechanism and a roller locking device, which is precisely the category of answer this risk deserves.
On an outward casement, rain strikes the outer face of the sash and runs off the outside of the building. The frame's work begins where the sash meets it, and it has three jobs that are often discussed as one. The outer seal keeps the bulk of the weather out. A drainage path takes whatever gets past that seal and carries it back outside — and that path has to exist in the extrusion, not just on the drawing. The inner seal is the one the water must never reach. Every outward casement in the ALPES range puts its effort on a different part of that chain.
On thermal numbers, be precise about what you are reading. The published K values — 1.6 for the C120, 1.7 for the C116, 1.3 for the AW90 — are system values, not whole-window U values, and they are not on an NFRC basis. A converted value is not a tested value. The C113 publishes no K value at all. If your project is being assessed on a whole-window figure, ask for a calculation on your actual configuration; do not compare a published number against a blank space and call it a result.
The outer face of an outward casement is outside. On a ground floor that is a chore; above it, it is an access problem; on some buildings it is a safety problem that ends in a rule rather than a preference. Window guides aimed at homeowners are blunt about this: the inability to clean the outer surface safely on upper floors is the standard objection to outward opening, and the ability to clean it from inside is the standard argument for inward opening.
The hardware industry already sells the answer, and it rarely reaches the window quotation. Egress easy-clean friction stays let the sash slide across its own frame so the outer face can be reached from inside the room. They appear in the same catalogues as standard stays, with their own width and weight ratings, which means they are a line item you can specify. If your brief includes upper floors, ask for them by name. If your brief includes upper floors and you also want secure night ventilation and external shading, the honest answer is not a cleverer stay — it is the other window.
The AW90 exists in this range for a reason, and the reason is the six sections above. It is the tilt and turn / inward opening window: 6060-T66 at 1.8 mm, a 90 mm frame, a 90 mm glass sash, a 72/4 mm mullion, Winkhaus hardware with an optional C-slot ROTO set, 360° locking point distribution and a dual-matrix eight-layer sealing system. It publishes the lowest K value in the range at 1.3. It is the only window here whose outer glass can be cleaned from inside the room, the only one that can carry an external screen or shutter, and the only one that can be left cracked open at night without leaving an aperture a person could pass through.
| If your brief includes… | Outward casement | AW90 tilt and turn |
|---|---|---|
| Upper floors with no external cleaning access | Ask for egress easy-clean stays; check local height rules first | Cleaned from inside; this is what the window is for |
| Secure night ventilation | Open means open; a restrictor gives a gap, not a mode | Tilt position: ventilation without an aperture |
| External roller shutter or external fly screen | Not generally available | Available |
| Interior sill must stay usable | Always clear, open or closed | Must be kept clear for the sash to swing in |
| Lowest published K value in the range | C120 at 1.6, C116 at 1.7, C113 not published | 1.3 |
| Published corrosion evidence | None published for the casement series | 240-hour salt spray test published |
One honest boundary: the 240-hour salt spray result and the 5,000 N shear strength belong to the AW90. They are published test results, not a project qualification, and they do not transfer to the C113, the C116 or the C120. If your coastal or high-wind project needs a corrosion or structural figure on a casement series, ask for it on that series, in writing, for your exposure.
All four windows below are 6060-T66 with PA66GF25 multi-chamber thermal breaks; the three casement series run at 1.8–2.0 mm wall thickness and the AW90 at 1.8 mm. The differences that matter are the ones that answer the six consequences above.
| Series | Frame width | Glass sash thickness | Mullion | Where the engineering effort went | Published K |
|---|---|---|---|---|---|
| C113 Outward-Open | 113 mm | 57 mm | 75/21 mm | Full glue injection with glued corner brackets; triple sealing; isothermal axis; CMECH hardware tested to 30,000 cycles | Not published |
| C116 Outward-Open | 116 mm | 81 mm | 58/22 mm | 28 mm oblique press line; 34–44 mm insulation strips; flat-channel drainage; welded corners; 304 high-load hinges; Wehag upgrade available | 1.7 |
| C120 Outward Opening System | 119 mm | 62 mm | 75/31 mm | Integrated sash and screen unit; injection-moulded structural adhesive; full square cavity; ROTO transmission box and anti-pry lock points; fall rope safety mechanism | 1.6 |
| AW90 Passive (inward) | 90 mm | 90 mm | 72/4 mm | 360° locking; dual-matrix eight-layer sealing; Winkhaus with optional C-slot ROTO; 240-hour salt spray; 5,000 N shear | 1.3 |
These four lines will separate a factory that has engineered your window from one that has only priced it. Send them with your opening sizes in millimetres and your glass build-up.
| Ask for | Why it decides the outcome | An answer that means nothing |
|---|---|---|
| Maximum sash width and height in mm, for this series, at this glass build-up | The stay sets the ceiling, not the profile, and every extra millimetre of glass lowers it | "We can make any size you need" |
| Stay or hinge rating per sash in kg, plus the groove standard and stack height | It is the load path, and it decides what you can still buy in year eight | A hardware brand name with no rating |
| Cycle-test figure, and whether it was run at that rated load | A bench number run unloaded tells you very little about your sash | "Tested to 30,000 cycles" with no load stated |
| K value: which standard, and system value or whole-window calculation | EN and ISO boundary conditions differ from NFRC; a converted value is not a tested value | "K 1.6" with no basis given |
Add three more as separate lines: whether an opening restrictor is included; whether an egress easy-clean stay is available for the sizes you are ordering; and whether the insect screen opens independently of the sash or is fixed to the same frame.
| Item | What we publish | What you still have to request |
|---|---|---|
| Alloy and temper | 6060-T66 across the range | — |
| Wall thickness | 1.8–2.0 mm on the casement series; 1.8 mm on the AW90 | — |
| Thermal break | PA66GF25; 34–44 mm multi-chamber strips on the C116 | Strip width in mm on the C113 and C120 |
| Geometry | Frame width, glass sash thickness and mullion for all four series | Maximum sash width and height at your glass build-up |
| Thermal | K 1.6 (C120), 1.7 (C116), 1.3 (AW90) — system values | K for the C113; a whole-window calculation for your configuration; SHGC, which is not published for any series |
| Hardware | CMECH with 30,000 cycles (C113); ROTO transmission box and anti-pry lock points (C120); Wehag upgrade (C116); Winkhaus with optional C-slot ROTO (AW90); 304 high-load hinges (C116) | Stay or hinge rating per sash in kg; groove standard and stack height; whether the cycle figure was at rated load |
| Corrosion and structure | 240-hour salt spray and 5,000 N shear, AW90 only | The same figures on whichever casement series you are buying |
| Screens and restraint | Mesh type by series; fall rope safety mechanism and roller locking device on the C120 | Independent screen operation; restrictor; egress easy-clean option on the other series |
A gap in a published specification is not a hidden weakness — it is a question that has not been asked yet. Turn this table into an attachment on your order. What is written into the order is what the window will be judged against; what is only printed in a brochure is an opinion.
Yes. The C113, the C116 and the C120 all open outward. The AW90 is the tilt and turn window in the range and opens inward, which is why it can carry an external screen, be cleaned from inside, and be left in a tilt position for secure ventilation.
Generally not. The sash swings into the space where an external shutter or external fly screen would sit. If external shading is part of your design, specify it at the same time as the window, because it will push you towards an inward opener.
ALPES does not publish a maximum sash size for the casement series, and we are not going to invent one. Published friction-stay tables from hardware makers put side-hung widths for a standard stay in the region of 500 to 700 mm, with the heavy-duty egress versions reaching around 1000 mm. Ask for the figure in writing against your glass build-up.
The glass usually performs better than the frame it replaces, so a larger glazed area often improves the overall number. The penalty arrives through weight: heavier glass pulls the permitted sash size down. That is why glass build-up, stay rating and maximum sash size have to be specified together.
That is a question for your local authority, not for us. Height-based restrictions on outward-opening windows are common and are widely cited in China for high-rise buildings and for buildings above 100 m. We can supply material and construction data, drawings and samples; we cannot certify your jurisdiction.
Give the maximum sash width and height in millimetres for that series at your glass build-up, together with the stay or hinge rating per sash in kilograms. Those two lines tell you more about whether the window will still be working in ten years than any other number on the sheet.
A casement is the simplest window there is — one sash, one frame, one direction. That simplicity is deceptive, because the direction quietly settles six questions before you get to choose anything else: where the screen lives, how big the sash can be, what a gust does, where the water goes, who cleans the glass, and what you are allowed to hang in the opening. Decide the direction first, and the choice between the C113, the C116, the C120 and the AW90 stops being a matter of taste and becomes a matter of matching a window to a building. Decide it last, and no amount of profile thickness will rescue it.
