Search for three panel sliding window standard sizes and you will get a chart: 72 x 48, 84 x 48, 96 x 60, and so on up the page. The chart is not wrong, but it answers a narrower question than the one you are actually asking. A three-panel unit is not a two-panel unit with extra glass bolted on — the number of tracks changes how much of it can open, and the width of each bay decides whether the opening is useful at all. Order the frame size correctly and the track count wrong, and you get a window that fits the wall perfectly and still leaves the room short of air.
Below is the sequence we walk buyers through: what “three panel” can legitimately mean, the ranges that three different markets actually publish, why converting a three-panel from inches is more dangerous than converting a two-panel, the clear-opening rule that no size chart prints, what really caps the width, which ALPES series carries which layout, and an order sheet you can paste straight into an RFQ.
The first thing to settle is that at least four different products answer to this name, and they do not open the same amount. In trade shorthand, X means a panel that slides and O means one that is fixed. A centre-fixed unit is XOX; an end-fixed unit is OXX or XXO; a unit where all three sashes move is XXX. North American catalogues also call the centre-fixed version a 3-lite slider or an end-vent slider, because the two vents sit at the ends. Australian and UK suppliers usually just print XOX.
There is also a fifth thing that gets called a three-panel window and is not one: three separate window units coupled together with mullions. That gives you two permanent vertical frame lines in the middle of your view and three independently operated sashes. It is a legitimate detail, but it is a different product from one frame carrying three sashes, and it is quoted differently.
| Layout | Tracks | What is fixed | Where the open glass has to go | Max clear opening |
|---|---|---|---|---|
| XO, two-panel baseline | 2 | One end | The vent slides over the fixed panel | 1/2 of frame width |
| XOX, centre fixed (end vent) | 2 | Centre bay | Both vents share the centre bay, so they trade off against each other | 1/3 of frame width |
| XOX on three tracks | 3 | Centre bay | Each vent runs on its own track, so both can park over the centre at once | 2/3 of frame width |
| OXX / XXO, end fixed | 3 | One end bay | The two vents stack behind each other over the remaining two bays | 1/3 of frame width |
| XXX, all three slide | 3 | Nothing | All three stack at one end | 2/3 of frame width |
| Three single units, mullion-coupled | Per unit | Depends on each unit | Each sash opens within its own frame | Up to 2/3, but you keep two mullions |
Read the last two columns again, because they are the whole article. Everything else on a three-panel size chart is negotiable; the clear opening is not. And notice that the same XOX drawing gives you one third or two thirds depending purely on whether the frame has two tracks or three.
There is no international standard for three-panel sliding window sizes. What exists is a set of catalog conventions that, usefully, converge. A Canadian installer’s size chart lists XOX units from 72 x 36 inches up to 144 x 72 inches. An Australian aluminium manufacturer publishes XOX as 1800–3600 mm wide by 600–1500 mm high. Convert the first into millimetres and the two land almost on top of each other: about 1.8 m to 3.6 m of width. That convergence is the closest thing to a “standard” you will find.
| Nominal call size (in) | Exact conversion (mm) | Common metric module (mm) | Where it appears |
|---|---|---|---|
| 72 x 36 | 1829 x 914 | 1800 x 900 | Smallest XOX in the Canadian chart, listed for condos and small offices |
| 72 x 48 | 1829 x 1219 | 1800 x 1200 | Listed by both a Canadian size chart and a Toronto manufacturer’s type guide |
| 84 x 48 | 2134 x 1219 | 2100 x 1200 | Canadian chart, apartment façades |
| 96 x 48 | 2438 x 1219 | 2400 x 1200 | Canadian chart, living and dining areas |
| 96 x 60 | 2438 x 1524 | 2400 x 1500 | Canadian chart; also the top of the Australian height band |
| 108 x 60 | 2743 x 1524 | 2700 x 1500 | Canadian chart, mid-rise residential |
| 144 x 72 | 3658 x 1829 | 3600 x 1800 | Top of the Canadian chart; matches the 3600 mm ceiling quoted in Australia |
Height is the quieter agreement: 600–1500 mm in the Australian chart, 36–72 inches (914–1829 mm) in the North American one. Past roughly 3.6 m wide or 1.8 m tall you have left the sliding-window catalogue and entered sliding-door or curtain-wall territory. The Australian guide makes the point neatly — at three-panel widths the window sizes overlap sliding-door dimensions, and the difference between a window and a door at that point is sill height and where the unit sits in the wall, not the frame dimensions. Worth remembering when a supplier quotes you a “door” for a window opening.
One inch is 25.4 mm. That part is arithmetic. The problem is that the converted number is not the number you order, and on a three-panel unit the error is multiplied by three.
Take a nominal 72 x 48. In millimetres that is 1829 x 1219. No metric catalogue stocks 1829; metric production runs in 100 mm or 300 mm modules, so the order becomes 1800 x 1200. You are now 29 mm narrower and 19 mm shorter than the drawing. On a two-panel unit that shortfall is absorbed by one bay; the clear opening drops from about 914 mm to about 900 mm and nobody notices. On a three-panel unit each bay goes from roughly 610 mm to 600 mm, and the clear opening — already only a third of the width — drops with it. Small, cumulative, and it lands exactly where codes carry minimums.
This is the part buyers get wrong most often, usually because the elevation drawing looks so generous. Glass that opens has to go somewhere, and it can only go where the tracks let it stack. The rule is simple: clear opening equals total frame width minus the width the open panels must stack into.
On a 1800 mm two-track XOX that means three 600 mm bays, one of them fixed in the middle. Slide both vents as far as they will travel and the total opening is still 600 mm — a third of the frame — shared between the two ends. A two-panel unit of the same width gives you 900 mm. A North American buying guide states the same comparison in percentages: up to about 33 per cent of total width for a three-lite, against up to about 50 per cent for a two-lite.
What you gain is direction rather than quantity. Air entering at both ends of a 3.6 m opening crosses the room in a way that air entering at one end does not, and on a wide façade that can matter more than the raw area. What you lose is raw area, and you should decide which one the room needs before you decide how many panels it has.
If the window is a required escape opening, do the arithmetic before committing. One third of 1800 mm is 600 mm. The figures most often quoted in US residential-code discussions are a minimum net clear opening of 5.7 sq ft (roughly 0.53 m²) with minimums of 20 inches wide and 24 inches high; Australian and UK codes set their own. We are repeating those numbers to tell you to check them locally, not because we can certify them. Size the unit so the clear opening passes, not the frame.
Size charts stop where they stop for a reason, and it is not modesty. Three things end the range.
A three-panel unit is three heavy panels, and every one of them hangs on rollers. ALPES rates the TS130 side-press window at 200 kg of load-bearing pulley capacity, the SL112/167 at 220 kg per sash, and the SL155 at 400 kg on a single-panel double-rail self-balancing twenty-wheel pulley, with a single sash up to 2800 x 2600 mm and an opening area up to 7.5 m². The SL126/182 platforms take a single sash to 2.5 x 3.0 m, around 7 m² of daylight area. Ask your supplier for the sash weight per panel in kilograms and compare it to the rated capacity. A supplier who will not give you a per-panel weight has told you what you need to know.
Wider bays want thicker insulated units, and thicker glass is heavier glass. The ALPES SL112/167 runs 24A insulated glass; the SL126/182(75) runs a 27A super-large insulated unit with inert gas filling. Those are real differences in both panel weight and thermal behaviour, and they move together — the configuration that gives you the biggest bay also puts the most load on the roller.
Three tracks need more depth than two, and this is where three-panel projects most often fail on site. On the ALPES range the SL112/167 goes from 112 mm at one or two tracks to 167 mm at three; the SL126/182 goes from 126 mm to 182 mm. If your wall cavity is 150 mm, no three-track option fits and you are back to two panels or a shallower series.
One trap worth stating plainly: depth is a property of the series, not a function of the track count. The four-track SL155 is 155 mm deep — shallower than the three-track SL126/182 at 182 mm. Do not let anyone size a wall on the assumption that more tracks always means a deeper frame.
ALPES publishes one dedicated sliding window series and four sliding door series. In practice that means three-panel spans up to roughly 2.4 m are usually built on the window platform, and anything wider — or anything you intend to walk through — moves to a door platform. Ask which platform your quotation is on, because the frame depth and the roller rating change with it.
| Series | Frame depth by track count | Published configurations | Sash / interlock and track | What it means for a three-panel |
|---|---|---|---|---|
| TS130 Side Press Window | 130 mm | One Fixed + One Movable / Middle Fixed + Two Sides Movable | Sash 75 mm, visible frame 26 mm, track height 53/31 mm, 200 kg pulleys | The only ALPES series published with a middle-fixed, two-sides-movable layout — the XOX end-vent. ROTO side-pressure hardware, eight-point locking, four-sided continuous sealing with sealant between top rail and frame. Confirm whether your unit runs two or three tracks; it changes the clear opening from one third to two thirds. |
| SL112/167 | One/two track 112 mm / three track 167 mm | Flexible fixed + movable panel configuration | Sash 53 or 75 mm, glass 43 mm, 24A insulated glass, 220 kg per sash | The shallowest route to three tracks. 45 mm high-ｄｒｏｐ bottom track with optional 85 mm water barrier — the one to look at where the opening is exposed to driving rain. |
| SL126/182(96) | Two track 126 mm / three track 182 mm | Sliding / lift-sliding | Sash 96 mm, high track 43 mm, low track 8 mm | Single sash to 2.5 x 3.0 m (~7 m²). The widest interlock of the group, so the heaviest sightline where the vents meet. Patented eave-style waterproof design and water-blocking bottom edge. |
| SL126/182(75) | Two track 126 mm / three track 182 mm | Sliding / lift-sliding | Sash 75 mm, high track 43 mm, low track 8 mm, 27A inert-gas insulated glass | Same depth as the (96) but a 75 mm narrow-edge interlock for a slimmer view. Butyl gasket at frame-sash joints, 38 mm pressure-line-free frame option. |
| SL155 | Four track 155 mm | Sliding | Sash 44.5 mm, glass 54.5 mm, 400 kg twenty-wheel pulley | The big-span option: single sash to 2800 x 2600 mm, opening area to 7.5 m². Four tracks in 155 mm — remember this is shallower than the three-track 182 mm above. |
A word on thermal performance, because it is where we have to be straight with you: none of the ALPES sliding series publishes a K-value in the material we hold. If you need a number for a compliance submission, ask for a calculated whole-window value for the exact three-panel configuration and glass build-up. For reference, the ALPES casement and tilt-turn figures that are published are K = 1.3 on the AW90 passive window, 1.6 on the C120 and 1.7 on the C116. If U-value is the deciding criterion on the project, a casement or tilt-turn will serve you better than any slider, and we would rather say that now than after you have ordered.
On an XOX layout the fixed bay in the middle is doing more than filling space.
Three bays also mean a longer bottom track, and a longer track is a longer thing to keep drained. The ALPES platforms handle it differently: the SL112/167 uses a 45 mm high-ｄｒｏｐ bottom track with an optional 85 mm water barrier, the SL126/182 offers a 43 mm high or an 8 mm low track, and the SL155 uses a passive check-valve that accelerates water out and resists backflow. Match that choice to the exposure, not to the look.
Because the clear opening is a third of the width, there is a floor below which three panels stop making sense — and it is higher than most people expect. Divide the frame by three and ask whether that bay is a useful opening.
| Overall frame size | Bay width (W/3) | Clear opening on two tracks | Verdict |
|---|---|---|---|
| 1200 x 1200 mm (about 48 x 48 in) | 400 mm | 400 mm | Too narrow. Three panels buys you two vertical interlocks and a bay you cannot usefully reach through. A 48 x 48 sliding window is better built as two panels. |
| 1500 x 1500 mm (about 60 x 60 in) | 500 mm | 500 mm | Still tight, and right on the boundary where escape-opening minimums live. At 60 x 60 sliding window proportions a two-panel unit gives you half again as much air. |
| 1800 x 1200 mm (about 72 x 48 in) | 600 mm | 600 mm | The practical floor. A 72 x 48 sliding window is the smallest three-panel size that appears in published charts on both sides of the Pacific. |
| 2400 x 1500 mm (about 96 x 60 in) | 800 mm | 800 mm | Comfortable. The range most three-panel specifications should be aiming at. |
| 3600 x 1800 mm (about 144 x 72 in) | 1200 mm | 1200 mm | Top of the published window range. At this size you are on door hardware, and sill height decides whether it is a window or a door. |
Most disputes over three-panel units come from two parties using the same words for different things. This table removes the ambiguity. Send it as the specification and ask the supplier to fill it in.
| Line | What to require | Why it matters | Red flag |
|---|---|---|---|
| 1 | Layout: XOX centre-fixed, OXX end-fixed, or all-three-sliding | Three products, three different clear openings | “Three panel” with no X/O notation |
| 2 | Track count: two or three, stated | On an XOX this alone moves clear opening from 1/3 to 2/3 | Track count not shown on the section drawing |
| 3 | Actual frame size, width x height, in millimetres | The only dimension that belongs on a purchase order | Quotation in nominal inches only |
| 4 | Design rough opening and clearance per side, in millimetres | Conventions run from about 6 mm to about 15 mm a side depending on market | “Standard clearance” with no number |
| 5 | Net clear opening, in millimetres, in writing | The number the room and the code actually care about | Not stated anywhere in the quotation |
| 6 | Bay width in millimetres | Tells you whether the opening is usable before it is built | Bays of unequal width not disclosed |
| 7 | Sash weight per panel, in kilograms | The input to every downstream hardware decision | Supplier cannot or will not provide it |
| 8 | Roller rating per sash, in kilograms, with the pulley type | ALPES rates 200 kg on TS130, 220 kg on SL112/167, 400 kg on SL155 | Rating quoted per unit rather than per sash |
| 9 | Frame depth in millimetres against available wall depth | Three tracks needs 167 mm or 182 mm on the ALPES range | Depth given for the two-track version when three tracks are quoted |
| 10 | Interlock width in millimetres | Two of these sit in your view; 44.5 mm to 96 mm across the ALPES range | Only the narrowest visible face quoted |
| 11 | Glass build-up, e.g. 24A or 27A with inert gas, and overall sash thickness | Drives panel weight, acoustics and thermal behaviour together | “Double glazed” with no air gap or gas fill |
| 12 | Track type and drainage: low 8 mm, high 43 mm, 45 mm high-ｄｒｏｐ, or check valve; water barrier height | Three bays is a long track to keep drained | No drainage detail on the section |
| 13 | Screen specification and which track it occupies | A screen panel takes a track, and on a three-panel unit that track may be the one you needed | Screen added after the track count is fixed |
| 14 | Which bay is fixed, viewed from outside | A mirror-image unit is a remake, not a fix on site | Handing not confirmed on the drawing |
| 15 | Written statement on exterior cleaning access for the fixed bay | The failure mode nobody plans for and everybody notices | Question deflected to “site to arrange” |
Generally yes, in the sense that the published ranges for three-panel units start where two-panel ranges are getting large. A Canadian chart runs two-panel units from 36 inches to 84 inches wide and XOX three-panel units from 72 inches to 144 inches; an Australian manufacturer lists two-panel from 900 mm to 2400 mm and XOX from 1800 mm to 3600 mm. The overlap in the middle is real, which is why the deciding factor should be the clear opening and the wall depth rather than the panel count.
There is no single published standard, but there is a strong convention: about 1800 mm to 3600 mm wide (72 to 144 inches) and 600 mm to 1800 mm high (24 to 72 inches). The most commonly listed sizes in that band are 72 x 48, 84 x 48, 96 x 60 and 108 x 60. Treat those as starting points from a catalog convention, not as a standard you can hold anyone to.
Usually not, and this is the question to ask first. In the most common layout — XOX, or end-vent — the centre bay is fixed and only the two end panels move. All-three-sliding units exist but need three tracks and give up the stiffness the fixed centre provides. On the ALPES range, the TS130 is published with both a one-fixed-one-movable and a middle-fixed-two-sides-movable configuration, so confirm which one is being quoted.
A three-panel slider is one frame with three sashes sharing tracks; you see interlock profiles where the sashes meet, and they can be as narrow as 44.5 mm. Three windows coupled with mullions are three complete frames, each with its own outer profile, joined by structural mullions — you see two wide vertical members and you pay for three sets of frame. Coupled units win on transport and replacement, and they let you mix operating types; the single-frame slider wins on sightline and on how the opening reads from outside.
Sometimes, but you have to check the clear opening rather than the frame. On a two-track centre-fixed unit the clear opening is a third of the width, so an 1800 mm unit gives you 600 mm and a 1500 mm unit gives you only about 500 mm. The figures most often quoted in US residential-code discussions are a minimum net clear opening of 5.7 sq ft with minimums of 20 inches wide and 24 inches high; other markets set their own. Verify against your authority having jurisdiction before specifying, and if the number is marginal, either widen the unit or move to a three-track layout that doubles the opening.
For a two-track unit, 112 mm or 126 mm of frame depth covers the ALPES sliding platforms. For three tracks you need 167 mm or 182 mm. If the cavity is 150 mm, the shallowest three-track option on this range will not fit as a three-track unit, and you should either redesign to two panels or choose a series whose three-track depth suits the wall — bearing in mind that depth is a series property, so a four-track frame is not automatically deeper than a three-track one.
Three-panel sizes live in a fairly narrow band — roughly 1800 mm to 3600 mm wide — and the band is the least interesting thing about them. What decides whether the window works is the layout notation, the track count, and the bay width that follows from it. Write XOX or OXX on the drawing. State the track count. Order in millimetres of actual frame, not nominal inches. Ask for the net clear opening in writing and check it against your code before you check it against your view. And if the wall is under about 170 mm deep, solve that before you solve anything else.
