How the clear opening works
A two-panel slider has one fixed panel and one that moves. Slide it fully and you get roughly half the structural opening, minus the interlock stile. That is the trade-off in one sentence: you never get the whole hole, but you never lose any floor space either.
Three-panel configurations exist, where two panels slide and stack against one fixed pane, and they push the clear opening past half. They cost more and they need a wider structural opening to make sense, but on an extension rear wall they're worth pricing alongside a bifold.
| Configuration | Clear opening | Suits |
|---|---|---|
| 2 panel, 1 sliding | ≈ half the opening | Most replacement openings |
| 3 panel, 2 sliding | ≈ two thirds | Wide openings, 2,400mm+ |
| 4 panel, 2 sliding centre | ≈ half, centrally | Symmetrical extension walls |
Rollers and track — the whole ballgame
Everything people dislike about old patio doors comes back to the running gear. A cheap slider uses small nylon wheels running directly on an aluminium track. They flat-spot, the track wears, and after a decade you're shoving the door with your shoulder.
A well-built one uses larger steel-cored, sealed-bearing rollers, an adjustable carriage so height can be corrected years later, and a track profile designed to drain. Ask three questions on any quote: are the rollers adjustable after fitting, are the bearings sealed, and does the track have drainage slots that can be cleared without dismantling anything.
- Adjustable roller carriages, reachable without removing the panel
- Sealed bearings rather than open nylon wheels
- A drained track with slots you can actually clean
- An anti-lift device so the panel can't be jacked off the track
- A hook-bolt lock engaging into a steel keep, not a plastic one
Glass: where a slider earns its money
Patio doors carry the biggest panes on most houses, so glass spec has more effect here than anywhere else. Our standard is an A-rated sealed unit with a warm-edge spacer and argon fill, and the inner pane low-emissivity coated so heat radiating outwards is reflected back into the room.
Panes at this size are also safety-critical, which under Building Regulations means toughened or laminated glass in the low-level zones. Laminated has a security benefit too — it holds together when struck rather than dropping out — and on an exposed rear elevation it's a sensible upgrade to price.
Security on a sliding door
The classic attack on a slider is lifting the moving panel off its track. Any door worth buying has an anti-lift block or interlocking stiles that make that impossible once the door is closed.
Beyond that, look for a hook bolt engaging into a steel keep at two or more points, laminated glass in the moving panel if you want the extra margin, and PAS 24 tested hardware. As with every other door on the house, the cylinder standard to look for is TS007 three-star where a cylinder is used.
Thresholds, drainage and the wet-carpet problem
A sliding door threshold has to do two jobs at once: let a panel run over it and stop water coming in. It does that with a stepped profile and drainage channels that take water back outside.
The failure mode is always the same — the drainage slots block with grit, water backs up in the track, and it finds its way over the inner upstand. It's not a manufacturing fault, it's maintenance, and it takes about two minutes with a brush a couple of times a year. If anyone offers you a fully flush sliding threshold on an exposed elevation, ask them exactly how it's drained before you say yes.
Fitting: what actually determines longevity
A slider is less forgiving than a hinged door. A hinged door out of true can be adjusted at the hinge. A sliding panel out of true binds along its whole travel.
That means the frame has to be packed level and plumb across its full width, fixed at proper centres, and never simply foamed into place. We pack, fix, then check the panel runs the full sweep with two fingers before we glaze and seal. If a fitter glazes before checking the run, you'll find out about it in year three.
Reading a patio door quote
Sliders are quoted per opening because width, panel count and glass all move together. What you want on the paperwork is the configuration, the overall frame size, the glass specification, the locking arrangement and what's included in the fitting.
Our fitting always includes removing the existing unit, disposal, packing and fixing the frame, sealing inside and out, making good the reveal, and a 10-year insurance-backed guarantee registered to your address. Anything on your quote that's silent about disposal and making good is a quote for part of a job.
Aluminium or uPVC frames on a slider
Sliding doors are the one product where the frame material argument has real substance, because the panels are heavy and the sightlines are what you're paying for. Aluminium is stiffer per millimetre of frame, so an aluminium slider can carry a bigger pane on a slimmer stile than a uPVC one can.
Against that, modern uPVC systems are thermally better per pound spent, because the multi-chambered profile is an insulator while aluminium needs a thermal break engineered into it. On a rear elevation where you want maximum glass and are prepared to pay for it, aluminium wins on looks. On a straight replacement where the priority is warmth and value, uPVC does the job.
There is no maintenance argument between them any more. Neither needs painting, both wipe clean, and both will outlast their hardware.
Living with a slider day to day
Two practical things people don't think about until they've got one. The first is the fixed panel. Half your opening is permanently glass, which is wonderful for light and inconvenient if you were planning to put a sofa or a dresser against that wall — you'll be looking at the back of it from the garden.
The second is cleaning. The outer face of the fixed pane is straightforward. The outer face of the sliding pane and the channel it runs in are less so, because you're reaching across a track. Sliders with a lift-out facility for the moving panel make this far easier, and it is worth asking whether yours has one.
On the other side of the ledger, a slider is the only one of the three garden doors that can be left open a few inches securely with a restrictor, which on a warm evening with a cat or a toddler in the house turns out to matter more than the spec sheet suggests.
Get a patio door quoted properly
Send the brick-to-brick width and we'll price the configurations that actually fit it, with the glass and locking spelled out on the quote.