You're planning an extension with a wall that opens straight to the backyard, and you've decided a stacker door is the way to go. The next question is how wide you can span before you hit structural, hardware, or weight limits.
The short answer is that uPVC stacker doors can span up to around 4.8 metres in a four-panel configuration, with two-panel and three-panel setups covering everything below that. But span is only one part of the spec. Panel height, glass weight, track design, and the structural support above the opening all factor into what's possible and what's sensible for your home.
This guide walks through the practical limits of uPVC stacker doors, what affects those limits, and how to spec a door that works for your opening. We manufacture these doors at our Campbellfield facility in Melbourne, and the questions below are the ones homeowners ask us most often when they're planning a big opening.
A stacker door is a multi-panel sliding door where the moving panels park behind each other at one end of the run, rather than sliding past each other. When you open it, the panels collect at the fixed end instead of running along the full track length.
That distinguishes it from three door types people often confuse it with:
Stacker doors come in two, three, and four-panel configurations. A two-panel door is usually one fixed panel and one sliding panel, giving you a clear opening of roughly half the door width. A three-panel door has two sliders that stack behind one fixed panel, giving you a clear opening of about two-thirds of the total width. A four-panel door, with panels stacking from both ends to the middle or all to one side, opens to around three-quarters of the total width.
The choice between stacker, bifold, and lift-and-slide comes down to the span you want, how wide you want the clear opening, and the finished look. For most residential extensions, a stacker door is a strong middle ground.
For uPVC stacker doors, the span limits work roughly like this:
Configuration | Typical span range | Clear opening |
|---|---|---|
| Two-panel | Up to 3.0 metres | Around 50% of span |
| Three-panel | Up to 4.2 metres | Around 66% of span |
| Four-panel | Up to 4.8 metres | Around 75% of span |
Larger spans are possible in some cases. They push against several limits at once:
If the span you want is close to or above 4.8 metres, it's worth a conversation with a manufacturer early. Sometimes the better answer at that size is a lift-and-slide door, which handles heavy panels more smoothly.
Standard panel widths vary by configuration:
Narrower panels within a configuration mean smaller glass units, lighter weight per panel, and smoother operation. Wider panels give you a cleaner look with less visible framing across the span.
Maximum panel height on uPVC stacker doors sits around 2.4 metres, with some manufacturers going to 2.7 metres for specific ranges. maximum panel height on the Weatherall stacker range.
The relationship between panel size and glass thickness matters. Larger panels need thicker glass to meet structural wind-load requirements, particularly on exposed sites. Standard double-glazed panels use 4mm glass on each side of a 12mm or 16mm spacer filled with argon gas. Larger or more exposed panels may need 5mm or 6mm glass, which adds weight and changes the hardware specification.
A wide stacker door asks a lot of the structure above it. The wider the span, the more load the lintel has to carry, and the tighter the tolerance for deflection.
For spans up to 3 metres, a standard timber or engineered lintel is usually sufficient, sized by your builder or architect. Over 3 metres you're generally looking at steel, either a single beam or a combined timber-and-steel member. Over 4 metres, engineering input is typically required to specify the beam and the support at each end. [VERIFY WITH CLIENT: the span threshold at which Weatherall recommends structural engineering sign-off.]
Two things matter as much as the beam itself:
Bring your plans to your door manufacturer before the lintel is specified, not after. The door spec influences the structural requirement, and agreeing them together is far easier than retrofitting.
Three and four-panel stackers need at least two tracks, because the stacking panels need somewhere to park behind the next panel over. Standard configuration has one sliding panel per track, so a three-panel door has a fixed panel on one track and two sliders on a second track, stacking together when open.
Which end the panels stack at is a design decision. You want them to stack away from where people will be sitting or moving through the space, because even stacked panels take up around 150 to 200 millimetres of width at the parked end. In most Melbourne homes the call is driven by kitchen island placement, outdoor furniture layout, or the direction of the yard's sightline.
Flush track options are worth asking about if wheelchair access, pram access, or simply a cleaner transition to the outside matters to you. The flush track sits level with the finished floor inside and a slight fall outside, so there's no step or raised track to trip over. The trade-off is a slightly less weather-tight seal than a raised track, which matters on very exposed elevations.
A large stacker door is a significant hole in the thermal envelope of the house. Even the best-specified door transfers more heat than the wall it replaces. Getting the glass and frame specification right matters more as the door gets bigger, because a poor spec scales up with the area.
Double glazing with Low-E coating and argon gas fill is the practical minimum for a stacker door in Melbourne. Whole-door U-values vary by size and configuration, but a well-specified uPVC stacker door with double glazing typically achieves a whole-door U-value in the range of 1.6 to 2.2 W/m²K. whole-door U-value on the Weatherall stacker range.] Weatherall's best-performing window product achieves a U-value of 1.4 W/m²K, which sets the benchmark for the range.
For comparison, an aluminium stacker door of the same size with similar double glazing typically sits between 3.5 and 5.0 W/m²K. The difference comes almost entirely from the frame: uPVC conducts heat at roughly one-thousandth the rate of aluminium, and a stacker door's frame is a large proportion of its total surface area.
Triple glazing is worth considering for stacker doors on south-facing or heavily exposed elevations, where the loss across a large area justifies the extra cost and weight. For most Melbourne installations, double glazing with Low-E and argon hits the right balance of performance, weight, and price.
Before booking a showroom visit, it helps to have these details to hand:
With those, a door consultant can walk you through what's possible at your opening size, whether a stacker is the right system or whether lift-and-slide would serve you better, and what the performance and cost trade-offs look like.
Large stacker doors are worth getting right the first time. Once the opening is framed and the beam is in, changing the door spec gets expensive fast. Bring your plans to the Weatherall showroom in Campbellfield and the technical team will spec the door to your opening, your elevation, and your energy target. If you are outside Melbourne, a phone consultation covers the same ground for regional Victorian projects.
