In window work the word elevation does not mean height. It means the flat two-dimensional view you get when you stand outside the wall and look straight at the opening. A french casement window and a twin casement window are the same object drawn two ways: two side-hinged sashes sharing one frame and one central mullion. The elevation is the sheet where those sashes, the mullion, the hinge sides and the swing arcs all get committed to paper before a single aluminium profile is cut. We covered the spec table an architect should lock down in a separate article; this one is about the drawing those specs are printed on.
A double casement looks identical to a single wide casement when closed, and identical to a fixed-plus-open pair when closed. The elevation is the one drawing that has to make those differences impossible to confuse. If the elevation is vague, the factory builds the wrong center condition and the site finds out on install day.
Before any dimension is drawn, the elevation has to name which double casement you mean, because the two common types are not dimensionally identical:
Both can carry the same overall width on the elevation. They do not carry the same center detail, the same water-management path, or the same hardware at the middle. The drawing must say which one in words, not only in lines.
A useful double casement elevation is not one rectangle. It is six layers stacked on the same view, each answering a different question for a different reader.
| Layer | What it shows | Why it is on the sheet |
|---|---|---|
| Overall frame | Full width and full height of the unit you see from outside | The envelope the wall opening has to accept |
| Center condition | Mullion centerline plus each sash width, equal or unequal | Decides which sash is master and where both lock |
| Reveal | How far the frame sits proud of each wall face (depth into wall) | Drives the interior return and exterior cladding, shown in section |
| Sightline | Visible frame width you actually see when closed | The number that decides how slim the window looks |
| Glass sightline | Clear glass area inside the sash | The view, light and egress number the code cares about |
| Swing arc | Radius of each sash swept outward from its hinge | The check against railings, walkways and wall returns |
Every ALPES casement series publishes a frame wall width — 119 mm for C120, 116 mm for C116, 113 mm for C113. That number is the depth the frame sits into the wall. It is a section number, not an elevation number. The elevation shows the face, and on the face the number that matters is the visible frame width, which is the second of the two mullion figures: C120 reads 75 mm depth with a 31 mm visible face, C116 reads 58 mm depth with a 22 mm visible face. The first figure is how much aluminium is buried in the wall; the second is what your eye measures across the mullion when the window is shut. Reading the wrong one is the single most common error on a casement elevation.
The casement window width you draw on the elevation is the overall frame width. The glass sash thickness (62 mm on C120, 57 mm on C113, 81 mm on C116) is the stack depth of the sash, not the visible glass. None of these three numbers is the other, and a drawing that prints only one of them leaves the next reader guessing which one.
ALPES builds its double casements from the outward-opening C-series. All three share the 6060-T66 profile at 1.8 to 2.0 mm and the PA66GF25 multi-chamber thermal break. What changes between them is the number the elevation has to carry.
| Series | Frame wall width (into wall) | Glass sash thickness (stack) | Mullion depth / visible face | Hardware on the elevation |
|---|---|---|---|---|
| C120 | 119 mm | 62 mm | 75 mm / 31 mm | ROTO transmission box and anti-pry lock points |
| C113 | 113 mm | 57 mm | 75 mm / 21 mm | CMECH red-dot handle, 30,000-cycle tested |
| C116 | 116 mm | 81 mm | 58 mm / 22 mm | Wehag with 304 stainless-steel heavy-load hinges |
All three open outward, so on the elevation the hinge sits on the exterior face and the handle sits on the interior face. Mark that explicitly, because a double casement drawn the other way around sends the swing into the room and the hardware to the wrong side of the wall.
A double casement has a master sash and a slave sash. The master carries the lock that receives the slave; the slave carries the strike. Which side each hinge lives on is the handing, and it must be drawn from a clearly labeled view — exterior or interior — because the industry has more than one convention and assuming the reader uses yours is how a whole run gets built backwards. The elevation should show, for each sash: hinge side, opening direction (outward), and which sash is master. When both sashes are equal width, say so; when one is wider, say why and which one is the active leaf.
Because all three ALPES casement series open outward, the elevation must sweep an arc outside the wall for each sash, with a radius roughly equal to the sash height. For a double casement the two arcs leave the central mullion and open to opposite sides. Check each arc against what is already outside: a balcony railing, a walkway, an exterior shade, a wall return, planting beds, or a soffit. An outward casement that conflicts with any of those is a drawing error the elevation was supposed to catch, not a site surprise.
Retail size charts often add a fixed clearance to the frame to get the rough opening — published guidance ranges from about 13 mm per side up to roughly 50 mm total, depending on the source and the product. Those numbers describe stock vinyl and wood windows, not an aluminium system window. ALPES is a system supplier: the jamb and reveal allowance is set by the series and the wall build-up, and it is not the same as a catalog chart. Put the frame size on the elevation and request the approved rough-opening allowance for the specific C-series from ALPES before the wall is framed. A number copied from a retail chart is the wrong number for a system window.
The drawing is a geometry document. It does not carry the performance numbers that belong to a specific tested configuration, and those must be requested separately:
| Put on the sheet | Red flag if missing |
|---|---|
| Overall frame width and height | Wall opened to the wrong size |
| Center condition named in words | Wrong mullion or water path built |
| Each sash width, equal or unequal | Master and slave mixed up |
| Handing from a labeled view | Whole run hinged backwards |
| Outward swing arcs drawn and checked | Sash hits railing or walkway |
| Approved rough-opening allowance from ALPES | Frame will not seat in the wall |
ALPES manufactures these system windows at a 100,000 square metre base across Foshan and Zhaoqing, and supplies project quantities directly from the factory. Send the elevation with the checklist above filled in, and the performance figures requested per configuration, and the drawing becomes an order instead of a guess.
