Put the C113 and the C116 spec sheets side by side and the first thing anyone notices is a pair of frame widths: 113 mm and 116 mm. Three millimetres. Most comparisons stop there, argue about which number is better, and walk straight past the line that actually separates the two windows — the one that reads Glass Sash Thickness 57 mm on one sheet and 81 mm on the other. That is a 24 mm gap, eight times the size of the difference everyone argues about, and it is the number that decides what glass you are allowed to put in the window. This is a way of reading two outward-opening casement sheets that look almost identical, so the question you send a supplier is about the right millimetres.
Both are outward-opening thermal-break casement windows built in the same factories. Both are extruded in 6060-T66 alloy at 1.8–2.0 mm wall thickness. Both use PA66GF25 polyamide insulation strips in a multi-chamber thermal break. Both are offered with a screen. On a printed specification sheet the pair reads like one window with the decimals moved.
They are not the same window, and the reason is visible in what each sheet chooses to publish. The C113 feature list talks about corner structure, glue injection, seam alignment and tested hardware cycles. The C116 feature list talks about a slim press line, a flush interior, insulation strip width, drainage, hinge material and handle options. Those are two different sets of priorities, and reading them tells you more than either headline number does.
| Line on the sheet | C113 Outward-Open Window | C116 Outward-Open Window | What it changes in practice |
|---|---|---|---|
| Frame width | 113 mm | 116 mm | How deep a reveal the section has to sit in. Three millimetres — see below. |
| Glass sash thickness | 57 mm | 81 mm | The room available for the sealed unit. This is the real decision. |
| Mullion | 75/21 mm | 58/22 mm | First figure is mullion depth (stiffness and span), second is the visible face. |
| Thermal K value | Not published | 1.7 | The only headline thermal figure in the pair. Ask for the other one before comparing. |
| Insulation strip | PA66GF25, multi-chamber | PA66GF25 multi-chamber, 34–44 mm | C116 publishes the strip width in millimetres. Ask for the same dimension on the C113. |
| Profile | 6060-T66, 1.8–2.0 mm | 6060-T66, 1.8–2.0 mm | Identical. No advantage either way. |
| Corner construction | Full glue injection, integrated glued corner brackets | Triple sealing strips with seamless welded corners | Two different answers to the question of where a corner lets water in. |
| Drainage | Not specified on the sheet | Flat-channel, obstacle-free easy drainage | Ask for the sill and drainage section of the C113 before assuming they match. |
| Screen | Black high-definition anti-PM2.5 mesh, standard | 80# black/grey stainless mesh; anti-PM2.5 optional | Filtration is the default on the C113 and an upgrade on the C116. |
| Hardware | CMECH, Red Dot design award, 30,000 cycles tested | German Wehag upgrade available; 304 stainless high-load hinges with built-in hardware groove | One published cycle figure on the C113, one published hinge material on the C116. |
| Handle | Not specified on the sheet | Baseless 90° handle or side-mount handle | Interior projection matters, because on an outward opener the handle is inside the room. |
| Sightline details | Not listed | 28 mm oblique press line; 14 mm flush interior sash-to-screen profile | The C116 is documented around slimness in a way the C113 is not. |
Frame width is the number that has to fit your wall. A 113 mm frame and a 116 mm frame need roughly the same depth of reveal, and 3 mm is inside the tolerance you will use up with shims, packing, plaster and a sill. If your opening is a straight replacement with a fixed reveal, measure it and check both, by all means. But if three millimetres is what decides your project, the decision is being made for the wrong reason.
There is one situation where frame width stops being cosmetic: a deep reveal with a fixed internal lining, or an elevation where the window has to land flush to a cladding line. Even then the honest question is not which catalogue number is smaller. It is what the installed depth measures from outside face to inside face, which is not necessarily the same number as the frame width printed on a sheet. Ask for a section drawing with the dimension you care about marked on it.
For anyone cross-shopping materials at the same time, the argument is not aluminium versus a vinyl casement window either. Changing material changes the entire calculation — different thermal expansion, different stiffness, different maximum sash sizes, different fixing details. A 3 mm difference inside one aluminium family is noise next to that.
The glass sash thickness on these sheets is the depth of the sash profile — the moving section that carries the sealed unit. 57 mm on the C113, 81 mm on the C116. Twenty-four millimetres, and it governs a chain that runs all the way through to the hardware.
Every sash has a glazing rebate — the channel that receives the sealed unit. Aluminium window specification guidance describes this consistently: the unit has to seat in the rebate with adequate engagement per side plus clearance for setting blocks and drainage, and it is the rebate depth that sets an absolute ceiling on how thick a unit you can fit. Sash depth is a proxy for that capacity. It is not the same measurement.
Neither ALPES sheet publishes a rebate dimension or a maximum unit thickness. That is the single most useful number you can ask for, and it is the reason we are not going to tell you exactly what glass each series accepts: it is on a section drawing, not on a product page.
Thicker build-ups are how you purchase acoustics and thermal performance. Published guidance of this kind relates unit thickness to the section depth needed: roughly a 20 mm air-filled unit at the shallow end, a 24 mm argon-filled low-E unit in the mid-range, a 30 mm build or a laminated acoustic build needing more depth again, and a 44 mm triple unit needing a deep residential section. Read those numbers as order-of-magnitude guidance from another source, not as a substitute for the rebate dimension on your own drawing.
If your brief says roadside elevation with acoustic laminate, or triple glazing, a 57 mm sash is a question you have to answer before you order, and an 81 mm sash is the more comfortable starting point. If your brief says standard double glazing, 57 mm is very unlikely to be the constraint and the whole discussion is academic.
Glass is heavy. The figure used in glazing calculations is about 2.5 kg per square metre for every millimetre of glass thickness, so a 30 mm build-up carries roughly 25 kg per square metre of glass before any frame weight is added. That mass lands on the hinges and the stay.
Two consequences follow, and both are specification traps. First, maximum sash sizes are published against an assumed glass thickness — specify heavier glass and the largest panel the system will carry comes down. Second, the hinge has to be rated for the load. The C116 sheet names 304 stainless high-load hinges with a built-in hardware groove. The C113 sheet names a hardware brand and a cycle count but publishes no hinge specification. If you are ordering a tall or wide vent in heavy glass, that is the question worth asking, not which frame is three millimetres narrower.
A small vent — the kind of opening written as a 24x40 casement window — will sit comfortably inside almost any build-up either series accepts, so sash depth barely registers. A tall 1.5 m vent glazed with acoustic laminate is where the 24 mm starts to matter. Sash depth is a decision only when the glass is thick or the sash is large; for everything else it is a detail you confirm and move on from.
The C113 lists a mullion of 75/21 mm. The C116 lists 58/22 mm. Read quickly, that looks backwards — the slimmer-looking window appears to have the chunkier mullion.
It is not backwards, because the two numbers do different jobs. The first is the depth of the mullion section, the dimension that decides how far it can span and how much load it carries before it moves. The second is the visible face you see from inside the room. On that reading: the C113 has a deeper mullion section at 75 mm with a marginally narrower visible face at 21 mm; the C116 has a shallower 58 mm section with a 22 mm face.
So the sightline argument between these two is a one-millimetre wash, and anyone selling you one over the other on the second number is selling you nothing. The 17 mm difference in the first number is real. For a long mulled run, a tall opening, or a bank where one mullion carries wind load across several bays, mullion depth and the question of a reinforcement ｉｎｓｅｒｔ belong in your enquiry, and the C113 section is the deeper starting point. For single, modest vents the mullion never gets exercised and this paragraph does not apply to you.
Both windows attack the same problem — air and water getting past a sash that sits on the outside of the building — but the two published feature lists spend their effort in different places.
The C113 sheet leads with structure: a full glue-injection process using integrated glued corner brackets to produce a seamless monolithic corner, triple sealing against wind, rain, noise and temperature extremes, and a claim that the glass centreline, the thermal break strip and the equal-pressure sealing strip all sit on one axis. That last line is worth understanding. Putting those three on a common isothermal axis is a way of cutting the cold bridge and the edge condensation that follows it. It is a stated design intent on a sheet; ask for the section that shows it.
The C116 sheet leads with the joint and the exit path: triple sealing strips with seamless welded corners, and a flat-channel, obstacle-free drainage system. Those are two answers to the two places a casement actually leaks — the corner where two gasket runs meet, and the sill where collected water has to leave. A welded gasket corner removes the butt joint that is the classic leak path. A flat, unobstructed channel is easier to keep clear than a stepped one.
What neither sheet publishes is tested performance: air permeability, water tightness, wind resistance, and the standard each was tested to. That is normal for a product page, but it does mean you cannot compare these two on weathertightness from the sheets alone. Ask for the test report with the standard named and the tested configuration described — and expect that configuration to be a specific size and glass build-up rather than a series name.
One thing both share because they open outward: the sash sits outside, so wind pressure presses the sash onto the frame instead of trying to lift it off, and the screen sits inside where you can reach it. The trade is that the exterior glass face is on the outside of the building, and the sill and head details do the water management.
The C113 names CMECH hardware, notes a German Red Dot design award, and publishes 30,000 cycles tested. The C116 offers a German Wehag upgrade and publishes 304 stainless high-load hinges with a built-in hardware groove. For context within the same family, the C120 outward-opening series uses a ROTO transmission box with anti-pry lock points — the point being that the range is not tied to a single hardware house, so the brand follows the series.
Two honest readings of that. A cycle figure is a bench test on the hardware, not a service life for your window — it tells you the mechanism was tested, not how long it will last in your climate. And there is no published cycle figure on the C116 sheet, which is not the same as saying it is untested. It means the number exists somewhere else, and you should ask for it rather than assume either way.
The handle difference is genuinely practical, because on an outward-opening window the handle is inside the room and projects into it. The C116 publishes two options — a baseless 90° handle and a side-mount handle — which is a low-projection answer to the conflict that catches people out: the handle fouling a roller blind, a shutter or a curtain that has to clear the sash. The C113 sheet does not specify. If your interiors sit tight to the reveal, get the handle projection in millimetres before you choose.
The C113 ships with the black high-definition anti-PM2.5 mesh as standard. The C116 ships with 80# black/grey stainless mesh and offers the anti-PM2.5 mesh as an option. Filtration is therefore the default on one and a paid upgrade on the other — worth knowing before you compare quotations, because you may be comparing two different screens.
A mesh count and a filtration claim are not the same kind of statement. The count describes the weave — how many openings per inch, and therefore how fine the aperture is and what it keeps out mechanically. An anti-PM2.5 claim is a filtration performance claim, and a performance claim without a test method and a result behind it is marketing. Neither sheet publishes an airflow figure, a filtration efficiency, or the standard the mesh was tested against. Ask for all three.
Two practical notes to finish on. Finer mesh passes less air and less light and collects more dust, so the filtration upgrade carries an ongoing cleaning cost. And on an outward-opening casement the screen sits inside, which means you open it to reach the handle every single time you use the window — so the screen action and its latch get more cycles than the window does. That is where the C116's published detail of the glass sash and screen sitting flush on a 14 mm interior profile is doing real work rather than cosmetic work.
The C116 publishes a thermal K value of 1.7. The C113 publishes nothing. If you read that as meaning the C116 insulates better, you have made a comparison the data does not support: you have compared a published number against an absence.
A thermal figure on a product page needs three things before it means anything. The standard it was calculated to — EN/ISO and NFRC use different boundary conditions, and a value produced under one is not interchangeable with the other. The size it was calculated at — a frame value and a whole-window value are different things, and the whole-window value moves with the dimensions and the glass. And whether it is calculated or tested. A K or U figure quoted without the standard, the size and the basis is not a number you can ｄｒｏｐ into a compliance submission.
There is one figure on the C116 sheet that supports its thermal story in a checkable way: 34–44 mm multi-chamber insulation strips. Strip width in millimetres is a physical dimension you can verify on a drawing, and it is a better proxy for what the thermal break is doing than any headline value. The C113 states PA66GF25 multi-chamber without publishing the width. Ask for it in millimetres for both and you will have an actual comparison.
And to be completely straight about it: not published is not worse. There is no thermal figure for the C113 in the material available to us, so there is nothing to compare. The action is to request a calculation for your size and your glass build-up, for both series, produced to the same standard — and then you have a comparison.
Everything above is a choice within one family. Before you make it, check that the family is the right one, because these are the things that disqualify both series:
If the brief is "I need to clean this from the inside, on a high floor", the answer is not the C113 and it is not the C116. It is the inward-opening side of the range: aluminium tilt and turn windows swing into the room, which is why they are the standard answer for upper floors, and why they also give you a tilt position for ventilation without a full opening. Choose the family first, then choose the series.
| If your brief is | Start with | Why | Confirm before ordering |
|---|---|---|---|
| Roadside or flight-path elevation with acoustic laminate | C116 | The 81 mm sash is the roomier starting point for a thick build-up | Glazing rebate depth and maximum unit thickness on the section drawing |
| Triple glazing or a wide-cavity unit | C116 | Same reason: capacity, not advertised performance | Rebate, plus the hinge rating for the extra mass |
| Standard double glazing, small to mid-size vents | Either | At this glass build-up the 57 mm sash is not a limitation | That the specified unit sits inside the published rebate |
| Long mulled run or a tall bank where the mullion carries wind load | Ask — starting from C113 | The 75 mm mullion section is the deeper of the two | Mullion depth, whether a reinforcement ｉｎｓｅｒｔ is needed, and the deflection limit |
| Air filtration is part of the project brief | C113 | The anti-PM2.5 mesh is standard rather than an upgrade | Filtration test method and result, plus the airflow figure |
| A thermal value has to go into a submission | C116 | It is the only one of the two with a published K value | Standard, calculation size and basis — and request the same for the C113 |
| Tight interior where the handle sits near a blind or shutter | C116 | Baseless 90° and side-mount handle options are published | Handle projection in millimetres for the option you are buying |
| Coastal or pool-side exposure | Neither, on these sheets | No corrosion figure is published for either series. The AW90 in the tilt-and-turn range publishes a 240-hour salt spray result and a 5,000 N shear figure | Coating specification, hardware material, and the test report for the exact configuration |
| Repeatable specification across many identical units at standard glass | Either | When nothing runs near a limit, fewer variables is the safer choice | That the mesh, hinge specification and finish are written into the order |
The fastest way to get a useless comparison is to ask which one is better. The fastest way to get a useful one is to ask for the same fourteen things twice. Put these in your enquiry, once per series, and insist the answers come back in the same units.
| Ask for | Why it matters | What a useless answer looks like |
|---|---|---|
| 1. Frame width measured outside face to inside face, in mm | This is what has to fit your wall | "Standard" |
| 2. Sash depth, and separately the glazing rebate depth, in mm | The rebate sets the glass ceiling; sash depth alone does not | The catalogue number repeated back |
| 3. Maximum sealed unit thickness in mm | Tells you whether your glass build-up fits at all | No answer given |
| 4. Mullion depth and visible face, both in mm | Span and sightline are two different numbers | One number when you asked for two |
| 5. Insulation strip width in mm, and material | The part of the thermal story you can verify on a drawing | "PA66" with no dimension |
| 6. K or U value with the standard, the calculation size, and whether calculated or tested | Without these three it cannot go into a submission | A bare number |
| 7. Air permeability, water tightness and wind resistance, with the standard and the tested size and glass | Performance is granted to a configuration, not to a series name | A class with no standard behind it |
| 8. Glass build-up written out in full, for example 6+12Ar+6 with low-E on surface two | Glass and frame have to be specified together, never separately | "Double glazing" |
| 9. Screen: mesh count, material, filtration test standard and result, and airflow | A filtration claim needs a method and a result | "Anti-PM2.5 mesh" |
| 10. Hinge material and rating, and maximum sash size and weight | Heavier glass shrinks the largest panel the system will carry | "Heavy duty" |
| 11. Handle type and projection in mm | Interior clearance is the constraint on an outward opener | A photograph |
| 12. Corner construction and drainage type described in words | These are the two places a casement leaks | A marketing name |
| 13. Finish specification, and any corrosion test result | Coastal and pool-side projects live or die on this line | "Powder coated" |
| 14. Which items are standard and which are upgrades | Otherwise you are comparing two different products | A price with no list of inclusions |
No. They differ by 3 mm in frame width and 24 mm in sash depth, and the published feature lists describe different priorities. The C113 sheet is built around corner structure, glue injection, axis alignment and a filtration screen as standard. The C116 is built around sightline detail, welded gasket corners, drainage and a published thermal value. Read them as two answers to two briefs rather than a small one and a large one.
It means there is nothing to compare it against. An unpublished number is not a bad number. Ask for a calculation for your size and glass build-up, produced to a named standard, for both series — and compare the insulation strip width in millimetres while you are waiting, because that is checkable on a drawing.
Ask for the glazing rebate depth and the maximum unit thickness for each series. The 81 mm sash on the C116 is the roomier starting point, but sash depth is not the same measurement as rebate depth, and neither page publishes the rebate. Nobody can answer this honestly from the two product sheets alone.
Check your local code before anything else. Outward-opening casements face restrictions at height in some jurisdictions, and regardless of the rules the exterior glass has to be cleaned from outside. If cleaning from inside is the requirement, look to the inward-opening tilt-and-turn side of the range instead of either of these two.
It means that hardware was cycled 30,000 times on a test bench. It is a hardware test result, not a service life for a window installed in your climate, and no cycle figure is published for the C116. Ask for it rather than assuming it does not exist.
At that size and with standard double glazing, neither sash depth nor mullion depth is ever the constraint, so pick on the things that differ every day you use the window: the screen, since filtration is standard on the C113 and an option on the C116; the handle projection against your blinds; and the finish.
If you take one line away from this comparison, make it this: the 3 mm is the argument people have, and the 24 mm is the one that matters. Frame width decides what fits your wall, and both of these fit roughly the same wall. Sash depth decides what glass you can carry, which decides what the window can do about noise and heat, which decides how heavy the sash is and what the hinges have to be rated for.
Everything past that is a choice about where you want the engineering effort spent: corner structure and a filtration screen on the C113, sightline detail, drainage and a published thermal value on the C116. Write your brief down in the order it matters to your project, send the same fourteen questions for both, and let the answers pick the window.
