A large sliding door is judged less by how it looks on the day it goes in than by how it moves five years later. This guide follows the commissioning stage of a multi-panel run — the levelling, testing and adjustment that happens after the glass is in and before anyone signs anything off.
Most of the attention on a sliding door project goes to sightlines, panel sizes and glass. Almost none of it goes to the twenty minutes at the end of the installation when the installer runs each panel from one end of the track to the other, again and again, feeling for changes in resistance. That is the stage that determines whether the door is a pleasure to use or a slow irritation.
The installation filmed for this guide is a four-panel slimline aluminium run on a single-storey garden room near Grasmere, opening onto open field. The building was still a shell — timber frame, boarded deck, breather membrane visible — which is exactly the right moment to fit large glazing, and exactly the right moment to commission it properly while everything is still accessible.
A sliding panel can weigh well over 200kg. All of that weight is carried on a small number of rollers running in a track that has to be level along its entire length. Get the levels right and a heavy panel moves under one finger. Get them fractionally wrong and the panel accelerates downhill, drags uphill, or wears its rollers unevenly until it starts to bind — usually two or three winters later, long after everyone has forgotten how it felt on day one.
This is why we treat commissioning as a distinct stage of the installation rather than a final look-over. The frame being in and the glass being fitted is not the finish line. The finish line is the door behaving identically at both ends of the track, with the interlocks meeting cleanly and the locking points engaging without being pushed.
Everything begins at the cill. On the project filmed here the track is set down into the timber deck structure rather than sitting on top of it, so the finished internal floor can run out level through to the terrace. That detail has to be agreed at survey stage, because the structural deck has to be built to accept it — it cannot be created later.
The track is packed and bedded along its full length and checked with a long level rather than a short one. A short level will happily report that each individual metre is fine while the run as a whole falls twenty millimetres from one end to the other. Drainage slots in the outer track are kept clear throughout; they are the reason a low threshold can be weathertight, and sealing over them is one of the most common causes of water sitting in a track.
Panels are glazed once the outer frame is fixed, packed and confirmed square. On a run of this size that means lifting large units into sashes with suction handling gear and two people, then setting the glass on toe-and-heel packers. Those packers are not spacers — they transfer the weight of the glass into the corners of the sash and stop the panel from dropping out of square over time. A panel that is glazed carelessly will never adjust out properly, no matter how good the track is.
In the film the installer runs a panel the full length of the opening and back, then does it again. It looks unremarkable. What he is testing for is any change in effort across the travel, any sound from the rollers, and whether the panel holds position when released. Those three signals between them catch almost every levelling or roller fault while it is still easy to correct.
“If a large sliding panel needs two hands, something is wrong. It is a levelling fault, not the nature of the product.”
Roller height is adjustable, usually through a concealed screw at the base of each stile. Adjusting it lifts or drops that corner of the panel, which changes how the interlocks meet and how the seals compress. It is quick work — provided the building is still open and the installer can reach the base of the panel from both sides.
That is why commissioning belongs at this stage of the build rather than after the finishes. Once the floor is laid, the plaster is on and the terrace is paved up to the threshold, the same adjustment becomes a careful, protected operation around finished surfaces. Doing it while the deck is still boarded costs nothing and gets a better result.
Protective film stays on the frames until the surrounding trades are finished, but it does not stay on indefinitely — extended UV exposure makes film difficult to remove cleanly from powder coating. Where we hand over to another trade, we agree who removes it and when.
At handover we show you the same tests the installer ran: how the panel should feel, how to lock it properly, where the drainage slots are and how to keep them clear. Sliding doors need very little maintenance, but the track is the one part that genuinely benefits from a brush out a couple of times a year, particularly in a rural setting where grit and leaf debris find their way in.
You do not need technical knowledge to judge a sliding door installation. You need to use it. Open and close every panel yourself, at both ends of the track, before anyone leaves.
| Check | What good looks like | What it means if not |
|---|---|---|
| Effort to move | One hand, the same at both ends | Track not level along its length |
| Released mid-travel | Stays exactly where you leave it | Fall in the track |
| Closed shadow gap | Even from top to bottom | Roller heights need setting |
| Locking | Engages with the handle alone | Keeps need adjusting |
| Reflections | Flat and undistorted across panes | Frame fitted with twist |
| Track base | Clean, drainage slots visible | Debris or sealant blocking drainage |
Filmed on site
The moment a glazed, fifteen-metre sliding run is first moved on its track — the commissioning and adjustment stage, filmed on a garden room build near Grasmere.
0:17 · Near Grasmere, Cumbria · September 2025
This is the stage homeowners feel every single day for the next twenty years, and the one that separates a competent fit from a genuinely good one. The frames are in, the units are glazed, and the installer is now running each panel end to end by hand — repeatedly — to prove the track, the rollers and the interlocks before anything is signed off.
What you are watching is a test, not a demonstration. A correctly commissioned sliding panel moves with one hand, at the same effort from one end of the run to the other, and stops dead where you let go of it. Any change in resistance across the track means the cill is not perfectly level or the rollers need setting, and that is corrected now — while the building is still open and everything is accessible.
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