A shower pan is the one component that touches everything else in the wet area: the drain below it, the walls above it, and the door measured from its front edge. Understanding what it has to do - shed water, connect to the waterproofing, and carry the door - explains why the choice is made on construction and geometry rather than on finish.
What a Pan Has to Do
Four jobs, in order of importance. It has to slope to the outlet so water leaves rather than pools. It has to connect to the wall waterproofing in a way that keeps water inside the shower. It has to carry the weight of a person without deflecting. And it has to provide a stable line for the door seal and, where a door is hinged, for fixings that will take a live load.
Every category of pan does those four jobs differently. A moulded pan arrives with the slope and the drain opening formed and a flange at the wall. A tile-ready pan arrives with the same geometry but is designed to receive tile. A site-built pan has the slope formed in screed and the waterproofing bonded to the drain flange and the walls.
The Parts That Decide Performance
Three features explain most pan failures. The slope, which should fall to the drain at a consistent rate; a pan that is level or dished will hold water regardless of the finish. The flange or bonding surface at the wall, which is what the waterproofing connects to; a covering that butts into the pan surface instead of lapping the flange is a leak path. And the support underneath, which for moulded pans is a continuous setting bed and for site-built pans is the sloped bed itself.
| Feature | What it does | Common failure |
|---|---|---|
| Slope | Sheds water to the outlet | Level or twisted pan; water pools at the perimeter |
| Flange | Connects pan to wall waterproofing | Wall covering butted into the pan instead of lapping |
| Setting bed | Supports the full underside | Spot bedding; flex, then cracking at the drain |
| Drain position | Meets the existing trap | Pan ordered without measuring the trap |
Moulded, Tile-Ready and Site-Built
A moulded pan in composite, acrylic or solid surface is the fast, predictable route: received pre-sloped, set on a continuous bed, connected and protected in a single visit. Its limits are the footprints offered and a fixed drain position.
A tile-ready pan keeps the factory slope but accepts tile, which suits a room where the floor finish has to continue into the shower. Its requirement is that the membrane connects to the pan's bonding flange in a continuous layer rather than being sealed over it. A site-built pan is the most adaptable and the most dependent on the installer, and it is the only route when the footprint matches nothing made.
Size, Geometry and the Door Above
The pan sets the width the door has to cover and the line its bottom seal runs along. Base footprints cluster around 60 in. x 30/32/34/36 in. for alcove replacements, with 48 in. x 32/36 in. for shorter alcoves and 36 in. x 36 in. or 42 in. x 36 in. for corners. The measurements that decide fit are the finished opening at three heights, the depth at both ends, and the drain centre taken from two reference walls.
Door type follows depth as much as width: a 30 in. deep alcove works with a sliding door but leaves little floor once a hinged door opens inward; from about 32 in. deep, hinged and pivot doors become comfortable. The full footprint list and what each size fits are set out in the shower pan sizes guide, with the measurement sequence in our guide to sizing a pan.
Drainage: Position, Trap and Access
The pan's outlet has to sit over the trap or the subfloor opening, and the drain position is fixed at manufacture. That is why centre, left, right and offset pans exist, and why measuring the trap from two reference walls is the first task. Where the trap has to move, expect to open the subfloor and check the joist direction before anything else.
Service access matters as much as position. A trap that cannot be reached becomes a demolition job the first time it blocks, so the pan should sit above a floor opening or a concealing panel rather than over an unbroken tiled floor. Plumbing provisions come from the adopted code published at iccsafe.org.
Setting a Pan So It Lasts
The sequence is short and unforgiving: prepare a flat, sound subfloor; confirm the drain position; set the pan on a continuous bed; level it in both directions; connect the drain without pulling the pan out of level; then install the wall covering so its bottom edge laps the flange. Nothing below the splash line should be fastened through the waterproofing.
Wet-area methods for that junction are published by the Tile Council of North America and catalogued on the Whole Building Design Guide; component test methods are published by ASTM International; and where a previous pan has leaked into the floor, the moisture guidance published by the EPA explains how far the assembly has to be opened.
Choosing Between the Types
Choose a moulded pan where the footprint is standard, the trap position can be matched, and the project needs to move quickly. Choose a tile-ready pan where the floor finish has to continue, or where the membrane system is already specified for the walls. Choose a site-built pan where the opening is genuinely non-standard, accepting the labour and the dependence on careful membrane detailing.
In all three cases the deciding facts are the same: the finished opening, the drain position, the subfloor, and the door that will sit on top. Those four are measured before anything is ordered - and the pan, the surround and the door are specified as one system rather than three separate purchases.
FAQ
What's the difference between a shower pan and a shower base?
In US retail use the words describe the same component: the floor of the shower that receives the drain. Trade usage sometimes narrows "pan" to a site-built or tile-ready receptor and "base" to a factory-moulded unit, which is a difference in construction method rather than in purpose.
What is the best type of shower pan?
The one that matches the project: a moulded pan for standard footprints and fast replacements, a tile-ready pan where the floor finish continues into the shower, and a site-built pan for genuinely custom openings. All three depend on a continuous support bed and a correctly lapped wall junction.
Is it possible to just replace a shower pan?
Sometimes. Where the replacement matches the footprint and drain position and the wall covering can be released at the bottom, the pan can be swapped with limited make-good. Where the pan has a flange behind the wall covering, the bottom course of tile or panel has to come off first.
Do I need to put anything under a shower pan?
Yes - a continuous setting bed, usually mortar or a purpose-made foam bed, so the underside of the pan is fully supported over a flat and sound subfloor. Spot adhesive or loose shims are the usual cause of a pan that flexes, squeaks and eventually cracks at the drain.
Send the finished opening at three heights, the drain centre from two walls and the subfloor type, and we will confirm the pan type, footprint and drain position that fits.
