Choose the door family from the shape of the opening before you compare a single product: how many sides are already closed, and which side the door can be fixed to. Those two facts decide which families are possible at all, and every comparison after that is a comparison within one family rather than between them.
Most buyers do it the other way round. They open a product page, compare finishes and widths, and only then discover that the opening cannot take that family - because the shape of the opening, not the product, decides which families are possible. An alcove with three walls, a corner with two, and a walk-in with one open side ask for different doors and different fixings, and no amount of comparison changes that.
Match the family to the opening
The opening's shape is defined by how many sides it already has. An alcove is closed on three sides, so it needs a door across a single face and little else. A corner is closed on two sides, which usually means a door plus a fixed panel arranged around the corner. A walk-in or open-side arrangement has one closed side or none, so the enclosure has to create the missing sides itself. Those three situations do not lead to the same product family, and they do not lead to the same fixing problem either.
Reading the shape first also exposes the constraint that will decide the family later: which sides the door can be fixed to. A sliding door needs a track line or a rail to travel along; a hinged door needs a fixing at the hinge side; a pivot door needs room for its arc on at least one side. If the opening does not offer the side that family depends on, the comparison ends there.
Alcove, corner and walk-in constraints
Each shape carries its own set of constraints, and they are constraints on the door rather than on the room.
Alcove openings
An alcove is the simplest case: one face to close, three walls to work against. The family choice then turns on how that face is used - whether the door has to swing into the room, travel along the face, or fold. Because the opening is closed on both sides, a door that relies on a wall at each end has both of them available, which is why sliding, hinged and pivot families are all usually possible here.
Corner openings
A corner reduces the number of walls to two and adds a second direction to seal. The enclosure usually becomes a door plus a fixed panel, and the corner itself has to be closed by the panel rather than by the door. The constraint that appears here is where the two glass elements meet: the door has to close against the panel, so the panel's position affects the door's family and its handing.
Walk-in and open-side openings
Where one side is open, the enclosure has to create the missing wall. That turns the decision into a choice about which sides are fixed panels and which are doors, and it is where the family question becomes a layout question: a single swing door against a screen, a fixed panel with a narrower door, or a sliding panel that uses the open side for travel. The door types guide covers how the families differ once the opening allows more than one of them.
What each family needs from the walls
The family also decides what the walls have to provide, and this is where an opening that looks possible becomes a problem.
| Family | What it needs from the walls | What to confirm before comparing models |
|---|---|---|
| Sliding | A line for the track or rail, and enough wall length for the panels to park | Where the track is fixed and what it is fixed to |
| Hinged | A fixing at the hinge side that can carry the door | What the hinge side is built from, and whether it is plumb |
| Pivot | Support at the pivot position and clearance for the arc | Where the pivot sits and what the door swings towards |
| Fixed panel | Edge fixings or a channel along the side it closes | How the panel is held at the wall and at the floor or tray |
Two of those requirements are about strength, and one is about geometry. A wall that cannot hold the fixing needed by the family rules that family out; a wall that is not plumb at the hinge position changes how the door closes; and a wall whose finish is not yet completed changes the measurements the door is made to. Where the wall's ability to hold a fixing is the open question, the guide to installing without wall studs covers what can and cannot be done, and where the opening itself is out of square, the guide to fitting a sliding door to an uneven wall explains what the door can absorb and what it cannot.
What to settle before comparing models
Four inputs decide the family, and until they are settled every product comparison is provisional.
- The shape of the opening - how many sides are already closed, and which side the door has to work against.
- The finished surfaces - measurements are taken on the finished wall and tray, not on what is behind them, so the family is chosen against the size the opening will finally have.
- What the walls can carry - the fixing each family depends on has to land on something that will hold it; this is a limit on the family, not a detail to solve later.
- How the space is used - who steps in and out, whether the door is operated from one side or both, and how much clear space the room can give to a door that moves.
Once those four are written down, the family usually selects itself, and the comparison that follows is between models of one family rather than between families. That is also the point where the commercial range becomes useful: the shower doors collection is organised by family and configuration, so it can be read against the opening rather than browsed at random.
Decision rule: with three closed sides, compare families freely; with two, plan on a door plus a fixed panel; with one open side, settle the arrangement before the family. Finish, width and hardware are comparisons inside that answer.