The phrase "slim frame" gets used as if it were a single measurement. In a sliding window it is at least three numbers, and only one of them is the line your eye actually reads. The other two decide whether the window fits your wall, whether the glass stays put, and whether the thing still slides in year three. Treating the word as one number is the most common way a slim-frame order goes wrong before anyone has drawn a line.
When a brochure says "slim", ask which of these three it is printing. They move in different directions and they are easy to confuse because two of them share the word "frame width".
| What the number measures | What it changes in your project | Real ALPES figures |
|---|---|---|
| Sightline at the meeting point (interlock) | How much aluminum you see where two panels overlap. This is the number people mean by "frameless". | Sliding-door family: 75 mm narrow central interlock and a 38 mm extreme slim frame on the SL126-182(75). |
| Visible sash / frame face width | The width of the visible face you look at from inside. Different from the interlock; a narrow face can still have a wide overlap. | TS130 sliding window: 75 mm sash width, 26 mm exposed frame width. |
| Frame wall width / depth into the wall | How deep the profile sits in the opening. This is about your wall build-up, not what you see. | TS130: 130 mm. Sliding doors: 112-167 mm (two/three track), 155 mm (four track). |
Notice the trap in the second and third rows: a spec sheet will print "frame width 26 mm" next to "sash width 75 mm". They are not the same measurement. The 26 mm is the short exposed leg of the outer frame; the 75 mm is the visible face of the moving sash. And "frame wall width 130 mm" is neither of those — it is how far the whole assembly goes into the wall. If you size the reveal off the 26 mm you will be wrong by a factor that no one notices until the drywall is up. Always ask which number is which before you quote a sightline to a client.
A casement or tilt-and-turn sash is pulled against a full-perimeter gasket and compressed shut. A sliding sash has to keep a running gap so it can move. That gap is a structural fact, not a quality lapse. It means the seal at the overlap can only be a contact seal — brush or fin that touches but does not compress the way a casement gasket does. So when a slim sliding window is also promised to be airtight and watertight at casement levels, you are asking two requirements to coexist that the sliding motion is always working against.
This is exactly why the TS130 is built the way it is. It is a side-press (side-pressure) sliding window: German ROTO hardware pulls the sash sideways out of the sliding plane and presses it against the frame seal when closed, instead of relying on a brush alone. The honest reading of ALPES's "casement-level sealing" claim is a comparison to an ordinary sliding window, not a claim that the window becomes a casement. The mechanism that earns that claim is an extra moving part that an ordinary slider does not have, and it is worth understanding before you assume a thin slider seals like a swing window.
One more honest point on performance numbers: ALPES publishes thermal K-values for its tilt-and-turn and casement families (1.3 for the AW90 passive window, 1.6 for the C120, 1.7 for the C116). Those figures belong to those opening types and those glass-and-frame combinations. The sliding family — the TS130 window and the SL sliding doors — does not publish a single K-value, because a sliding configuration's thermal result depends entirely on the glass build-up you specify. Do not let anyone transfer a casement K-number onto a slider. Ask for the calculated value for your exact configuration.
It is worth stating plainly: the only true sliding window in the current catalog is the TS130. The genuinely slim interlocks that people picture when they say "frameless sliding" live in the sliding-door family. That is not a weakness to hide — it is a planning fact. If your project is a window opening, the TS130 is the slider; if it is a large glazed wall, the SL sliding doors carry the thin-interlock story, and the two should not be conflated in a spec.
| Series | Visible face / interlock | Frame wall width | What to read from it |
|---|---|---|---|
| TS130 side-press window | 75 mm sash, 26 mm frame leg | 130 mm | The sliding window option; side-pressure seal via ROTO. |
| SL126-182(75) | 75 mm narrow edge, 38 mm extreme slim frame, 75 mm central interlock | 126 mm (two track) / 182 mm (three track) | Thinnest interlock story; door family. |
| SL155 | 44.5 mm sash width | 155 mm (four track) | Slim sash face but deep wall footprint. |
A counter-intuitive fact falls out of that table: the four-track SL155 has a 155 mm frame wall width, while the three-track SL126-182 has 182 mm. More tracks does not mean a deeper profile. Frame depth is a property of the series, not a function of how many tracks you stack. Anyone who sizes a rough opening by counting tracks will be surprised, and the surprise shows up as a wall that will not close.
A slim profile is not free aluminum removed; it is aluminum moved. Take it out of the visible face and the stiffness has to go somewhere else — into the wall of the profile, into the sash, into reinforcement at the corners. The load that drives all of this is the glass. A workable rule of thumb used across the industry is about 2.5 kilograms per square metre for every millimetre of glass thickness. A 6 mm plus 24 mm air plus 6 mm insulated unit therefore weighs roughly 30 kilograms per square metre before you add the frame. Treat that as a planning estimate, not a product claim.
That estimate is why the glass-thickness ceiling is decided by the glass rebate — the channel cut into the sash — and not by the visible sash thickness. A 55 mm sash thickness on the TS130 is the build-up of the sash, not the depth available for glass. The number that caps your glass is on the section drawing, and it is the first thing to ask for if a slim look is pushing you toward thicker, heavier insulating glass. This is also where the maximum sliding window size is really set: not by a size chart but by what the sash, the rollers and the glass weight will support together. A larger panel is a heavier panel, and a heavier panel is a different hardware and frame calculation, not the same window made bigger.
A slim frame in a dark finish is the look most mood boards ask for, and it is the look most often specified from a small chip under showroom lighting. A 2 metre black frame in direct daylight is not the same colour as that chip, and a slim profile shows more glass edge and more frame line, so any mismatch is bigger, not smaller. Dark powder-coated aluminum also absorbs more heat and expands more than the room around it; aluminum's lineal expansion runs about twice that of steel, so a long slim dark frame needs larger movement joints than a white one. These are direction-of-effect facts from general building-science knowledge, not ALPES-specific ratings — confirm the exact figure with your local cladding and glazing advisor.
For a sliding window black finish, the safe move is to approve the colour against a full-length sample in the daylight it will live in, and to write the movement-joint size into the order rather than leaving it to the installer's habit. Slim plus dark is a design choice that is perfectly achievable; it just is not the same specification as slim plus white.
Slim framing earns its cost when the view or the daylight is the product — a glazed wall facing a garden, a corner that wants uninterrupted glass, a room where the frame reads as clutter. It earns less when the opening is small, partially hidden by furniture, or when the performance envelope (sealing, thermal, acoustic) is doing heavier work than the sightline. A triple sliding window configuration is a good example: three panels multiply the number of overlaps and interlocks, so the slim-interlock decision is felt three times over, and the sealing and drainage at each overlap matter more than the single line you would worry about on a two-panel unit.
| Choose slim framing when | Hold off when |
|---|---|
| The glazing is a primary view or daylight source | The opening is small or mostly behind furniture |
| You can specify the glass build-up up front | Glass thickness is still "we will decide later" |
| You have drawn the wall build-up and movement joints | The reveal and track seating are left to site |
| Sealing is understood as a state set by adjustment | Sealing is assumed to be permanent from the factory |
A slim-frame sliding enquiry should ask for the numbers that decide whether the look survives contact with the building. The right-hand column is the answer that tells you nothing — the one to push past.
| Ask for | Why it matters | Answer that tells you nothing |
|---|---|---|
| Sightline and visible face, named separately | They are different numbers; one is not the other | "It is a slim frame" |
| Frame wall width / depth | Sets the rough opening and wall build-up | "Standard size" |
| Glass rebate depth from the section drawing | Caps how thick your glass can be | "It takes double glazing" |
| Calculated K-value for your glass build-up | Sliding family has no single published figure | "Same as our casement" |
| Roller load rating per sash, and glass weight | Rating is per sash and glass-driven | "Heavy duty" |
| Movement-joint size for the finish you chose | Dark slim frames expand more | "Standard installation" |
Not by definition. Strength comes from profile wall thickness, alloy, corner construction and reinforcement, not from how wide the visible face is. A slim face can be a thick, well-braced section. Ask for the section drawing rather than judging from the sightline photo.
An ordinary slider cannot match a compressed casement gasket, because the slider must keep a running gap. A side-press slider like the TS130 closes that gap by moving the sash against the seal when shut, which is why it is described as casement-level — a comparison to other sliders, not a claim to be a casement.
No. Thermal performance is set by the glass build-up, the insulation strip and the overall system, not by the visible face width. The sliding family does not publish a single K-value; request the calculated figure for your exact configuration.
Because the current sliding window is the TS130, while the slim-interlock engineering (38 mm extreme slim frame, 75 mm central interlock) sits in the SL sliding-door family. Match the opening type to the product rather than assuming the thinnest line is available in every category.
Frame width versus sash width versus frame wall width. They are three different measurements with similar names, and mixing them up is how reveals and rough openings get sized wrong.
No. The four-track SL155 is 155 mm deep while the three-track SL126-182 is 182 mm deep. Frame depth is a property of the series, not the track count.
Numbers cited as ALPES product figures (profile grades, widths, track heights, roller ratings, published K-values) are taken from the manufacturer's catalog. Figures described as industry rules of thumb (about 2.5 kg per square metre per millimetre of glass, aluminum expanding about twice as fast as steel) are general engineering estimates for planning, not ALPES product claims, and should be confirmed against your project's glass specification and local advisors.
