Specify a patio door as five coupled choices and the comparison between suppliers becomes almost mechanical:
Colour, handle style and mesh type all matter, but they are downstream. If the first five are right, the door works; if one of them is wrong, no finish will save it.
Every extra track lets one more panel move, but it also widens the frame you have to fit into the wall, adds a rail you have to clean, and adds rollers you eventually have to adjust. The useful comparison is not the overall door size - it is the clear opening left once interlocks, handles and parked leaves are counted.
| Track count | ALPES frame depth | What you gain | What you pay for it |
|---|---|---|---|
| Two tracks | 112 mm (SL112/167) or 126 mm (SL126/182) | Simplest sill, fewest cleaning points, slimmest wall penetration | One leaf always stays fixed - you never get more than roughly half the span open |
| Three tracks | 167 mm (SL112/167) or 182 mm (SL126/182) | Two leaves stack behind a third, so the opening can sit off-centre | Deeper frame to build into the wall, and three rails to keep clear |
| Four tracks | 155 mm (SL155) | Panels stack to one or both sides for a genuinely panoramic opening | Most rollers and interlocks to maintain; needs a real structural check on the head |
One thing worth noticing in that table: the four-track SL155 is shallower than the three-track SL126/182, because they are different systems rather than deeper versions of the same one. Frame depth does not rise in a straight line with track count, so never assume a four-track door needs more wall depth than a three-track door - check the specific system.
For a balcony sliding door on a standard opening, two tracks are usually the honest answer: one moving leaf, one fixed, minimal sill to keep clean. Move up to three tracks when the patio is wide enough that a permanently fixed panel starts to feel like a wall. Reserve a four panel sliding door for the cases where the whole point of the opening is that it disappears - a pool terrace, a garden elevation, a villa living room that opens end to end.
A patio panel is far heavier than it looks. The SL155 is rated for a single sash up to 2800 mm wide by 2600 mm high, with an opening area of up to 7.5 square metres. Once the insulated glass unit is in that sash, the entire load travels through a handful of wheels running on a rail around 40 mm wide - and it does that every single day.
Lift-and-slide deserves its own line in the enquiry, because it is not the same product as standard sliding. On the SL126/182 the opening method covers both sliding and lift-sliding: the handle rotation lifts the sash clear of its seals so a heavy panel glides on the rollers, then sets it back down onto continuous gaskets when you lock it. That is what makes a three-metre-tall leaf operable by one person, and it is also why the seals last - they are not being dragged across the frame on every opening.
Ask four questions here: what is the rated load per sash; how many wheels carry each sash; whether the rollers can be adjusted without taking the leaf out of the frame; and whether the quoted capacity is per roller or per sash. That last one is where undersizing usually hides.
Almost every "my patio door leaks" complaint is a threshold and drainage problem wearing a different costume. The relevant details on the ALPES systems are specific, and they are not interchangeable:
| Threshold feature | Where it appears | What it is for |
|---|---|---|
| Low track, 8 mm | SL126/182 (both 96 mm and 75 mm sash versions) | Near-level passage for wheelchairs, prams and bare feet |
| High track, 43 mm | SL126/182 (both versions) | Exposed terraces where wind-driven rain needs somewhere to sit and drain |
| 45 mm high-ｄｒｏｐ bottom track | SL112/167 | Instant drainage by gravity rather than by weep holes alone |
| Optional 85 mm water barrier | SL112/167 | Fully exposed elevations and pool decks that get hosed down |
| Passive check valve drainage | SL155 | Speeds water out and stops it flowing back in under wind pressure |
| Patented eave-style waterproof design plus bottom track water-blocking edge; interchangeable drip-eave inserts on the 75 mm version | SL126/182 | Keeps the head and the sill joint out of the water path |
Be honest with yourself about the site before choosing. A genuinely flush threshold on an exposed patio is a drainage problem, not a convenience feature. If the terrace falls toward the house, or the door faces the prevailing weather, take the higher track or the water barrier and accept the step. If step-free access is a hard requirement, pair the low track with a covered soffit, a drained channel in front of the door, and a written confirmation of where the water goes.
All four ALPES sliding door systems use 6060-T66 profiles with PA66GF25 polyamide thermal break strips in a multi-chamber layout. The glass pocket differs by system, and that pocket is what limits your glazing choice:
Here is the number to be careful about. ALPES publishes thermal K-values for its casement and tilt-turn systems - 1.3 for the AW90 passive window, 1.6 for the C120, 1.7 for the C116 - but no K-value is published for the sliding door range. Rather than invent one, ask for the whole-door U-factor and solar heat gain coefficient calculated for your exact size and glass build-up, and make it clear you want the whole-product figure, not a centre-of-glass value. The two are not comparable, and quoting one when the other was asked for is the oldest trick in the window trade.
There is also a structural ceiling on how well any slider can seal. A sliding leaf has to move, so it seals with brushes and sliding gaskets rather than the compression seal a casement or tilt-turn gets. Lift-and-slide narrows that gap considerably because the seals are only compressed when locked, but the honest comparison is slider against slider, not slider against casement. If the thermal target is the binding constraint on your project, say so at the beginning - the right answer may be a different product family rather than a different sliding door.
On the SL126/182 with the 75 mm sash, locking is a multi-point system with stainless steel locks sitting in precision-cast reinforced casings. The sliding door with lock specification you send out should cover more than the lock itself: where the lock points engage, whether the handle is keyed on the outside, and whether you can still lock the door with the insect screen closed.
Then decide which leaf is the traffic leaf. This sounds trivial and causes more daily irritation than any other choice in the door. Map it before you order:
Hardware across the range comes from ROTO and Winkhaus in Germany, plus CMECH and Wehag, so named hardware brands can be written into the contract rather than left as an adjective in a brochure.
| System | Profile | Frame depth | Max single sash | Best fit |
|---|---|---|---|---|
| SL155 | 2.2-2.5 mm, 6060-T66 | Four track, 155 mm | 2800 x 2600 mm, up to 7.5 sqm opening | Panoramic villa and pool-terrace openings where the view is the brief |
| SL112/167 | 1.8-2.5 mm, 6060-T66 | Single/two track 112 mm, three track 167 mm | Driving capacity up to 220 kg per sash | Exposed patios that need the 45 mm high-ｄｒｏｐ track or the 85 mm water barrier |
| SL126/182 (96 mm sash) | 2.0 mm, locally reinforced to 3.0 mm | Two track 126 mm, three track 182 mm | 2.5 x 3.0 m, roughly 7 sqm of daylight | Tall, heavy leaves that need lift-and-slide, plus wind pressure resistance |
| SL126/182 (75 mm sash) | 2.0 mm, locally reinforced to 3.0 mm | Two track 126 mm, three track 182 mm | Sash width 75 mm, 38 mm slim frame option | Slim-sightline patios where 27A gas-filled glass is specified |
Standard colours across the range are Ice Cream White, Aurora Gray, Starry Sky Gray and Brown Coffee, with custom matching available. If the patio faces the sea, raise the finish and the fastener material at the same time as the colour - the frame coating and the hardware should be specified together, not separately.
Sliding doors are excellent at some things and quietly poor at others. Say no to a slider in these four situations:
Sliding wins when you cannot give up floor or terrace space to a swing arc, when the opening is wide enough that a fixed glass wall with one moving leaf is the design intent anyway, and when the view matters more than the last decimal place of air tightness.
Corrosion resistance is a test result, not a claim. ALPES documents a 240-hour salt spray corrosion resistance test and a 5,000 N shear resistance figure on its AW90 passive window; ask for the equivalent test documentation for the finish and hardware package on whichever sliding door you are buying, because the frame, the rollers and the fasteners do not age at the same rate.
This is the SL112/167 territory: the 45 mm high-ｄｒｏｐ bottom track for instant drainage, with the optional 85 mm water barrier where the terrace gets hosed down or the door takes weather head-on. Pair it with the eave-style waterproof detail on the SL126/182 if the head of the opening is also exposed.
Glass does the work here. The SL126/182 with the 75 mm sash takes 27A super-large insulating glass with inert gas filling, which gives you room for a solar-control coating and a wider cavity than the 24A unit in the SL112/167. Ask for the solar heat gain coefficient for the exact build-up and check it against the orientation before you commit.
Wall thickness and profile geometry decide this. The SL126/182 is locally reinforced up to 3.0 mm in critical zones specifically for wind pressure resistance, and the SL112/167 uses a frame-enclosing-sash structure that interlocks and reinforces the panels against each other. Give the factory your design wind pressure and the required water penetration and air leakage class - those are project inputs, not catalogue defaults.
| Line | What to state | Red flag in the reply |
|---|---|---|
| Opening | Finished width at head, middle and sill; height at both jambs and centre; diagonal check | A quote based on a single width with no tolerance stated |
| Configuration | Track count, which panels move, which side they park, which is the traffic leaf | "Standard configuration" with no drawing |
| Sash size and weight | Largest single sash in mm, estimated panel weight, rated roller capacity per sash | Capacity given per roller rather than per sash |
| Threshold | High or low track, water barrier, and the direction the terrace falls | A flush threshold offered for an exposed elevation with no drainage plan |
| Glazing | Pane build-up, spacer, coating, gas fill, safety treatment | "Double glazed" with no thickness or cavity dimension |
| Thermal | Whole-door U-factor and SHGC for this exact size and glass | A centre-of-glass figure presented as the product rating |
| Ratings | Wind load, water penetration and air leakage class required by your code | Test certificates for a different system or a smaller size |
| Hardware | Named brands for rollers, locks and handles - ROTO, Winkhaus, CMECH, Wehag | "German hardware" with no brand named in the contract |
| Screens | Mesh type, mesh track position, whether the door locks with the screen closed | Screen added as an afterthought once the frame is made |
| Finish | Colour, coating type, and the corrosion test document for coastal sites | "Standard finish" with no test hours quoted anywhere |
With a PA66GF25 thermal break, an insulated glass unit and a proper sealing layout, yes for most climates. The honest caveat is that a sliding leaf cannot compress into its seals the way a casement can, so if your project has a hard U-value target, get the whole-door figure for your exact configuration before you fall in love with the design.
Two panels on two tracks for a standard opening, three tracks when the span is wide enough that a permanently fixed panel reads as a wall, and four tracks only when the whole point is that the opening disappears. Every extra track is another rail to clean and another set of rollers to adjust.
The handle lifts the sash off its seals before it rolls, then drops it back onto them when you lock. It is offered on the SL126/182 and it is worth specifying once a single sash gets large - around the 2.5 x 3.0 m mark - because it is what keeps a heavy panel moving with one hand and stops the seals being dragged on every operation.
The SL126/182 offers an 8 mm low track, which is about as close as a sliding door sensibly gets. Whether you should use it depends on exposure: on a sheltered, covered terrace, yes; on an open elevation facing the weather, take the 43 mm high track, or the SL112/167 with its 45 mm high-ｄｒｏｐ track and optional 85 mm water barrier.
If the door separates conditioned space from outdoors and you care about condensation or energy use, yes. All four ALPES sliding door systems are thermally broken as standard with PA66GF25 strips; what varies is the glass cavity - 24A on the SL112/167, 27A with inert gas on the SL126/182 in the 75 mm sash.
Specify drainage first, then maintain it. A passive check valve that cannot backflow, a high-ｄｒｏｐ track that clears by gravity, and a water path you can actually see and flush are worth more than any cleaning schedule. On site, test the drainage with water before the installers leave, and check roller adjustment at the same time.
