Key takeaways
- A setdown exists so the finished floor inside a shower or bath recess finishes below the adjoining floor, which lets water that escapes the enclosure drain back rather than run out into the room.
- The fall has to be built into the structural substrate or the screed, because membrane thickness and tile adhesive are not a lawful or reliable way to create it.
- Waste selection and setout should be confirmed before the slab or the timber floor is cut, since the trap depth, outlet diameter and grate style all constrain how shallow the recess can be.
- Where the recess is too shallow for the waste and the required fall, the fix is usually a raised perimeter or a different waste, not a thinner screed.
- Setdown dimensions, membrane termination and waste sealing all need to be documented before the waterproofer and tiler start, because rectification after tiling means demolition.
A shower setdown is not a tiling detail. It is a substrate decision, made at slab pour or floor framing stage, that fixes the fall, the finished floor level and the position of the waste. By the time the waterproofer arrives, the geometry of the recess has already decided whether the system can drain properly.
That is why setdown faults surface so late and cost so much. A membrane is a thin, flexible layer. It will follow whatever shape the substrate gives it, including a flat spot, a backfall or a shallow recess that leaves no room for the trap. It cannot create fall, and it cannot recover height that was never there.
This article deals with the substrate and the waste layout: how deep the recess needs to be, how the fall is formed, how the waste is selected and set out, and what to check before the trades that follow take over the room.
Why a setdown exists at all
The purpose of a setdown is containment. Water that escapes the shower screen, the bath lip or a hose draped over the edge has to be able to drain back to the waste instead of running across the bathroom floor and into the adjoining room.
A recessed floor achieves that by making the wet area the low point. The finished floor inside the shower or bath zone sits below the adjoining floor, so spillage and spray that crosses the boundary runs back towards the waste by gravity rather than sitting against the doorway or the wall base.
Where a setdown is not used, the same outcome has to be achieved another way, typically by a raised perimeter or hob, or by a linear waste at the entry with the whole room graded. Whichever approach is taken, the principle is the same: the wet area must be the low point, and it must drain.
Fall belongs in the substrate, not in the finishes
A common failure is trying to build fall out of the layers that sit on top of the membrane. Tile adhesive is not a grading material. Membrane thickness is not a grading material. Neither is applied to a controlled thickness, and neither is intended to carry the drainage grade for a wet area.
The fall has to be formed in a layer that is set out and checked: the structural slab where the recess is cast in, or a screed laid over the substrate before the membrane goes on. That layer is what the waterproofer and the tiler both work to, and it is the layer that determines whether water reaches the waste.
The minimum fall required is set by the relevant standard and by the membrane manufacturer’s system requirements. Those documents do not always agree, and where they differ the more onerous figure governs. Check the current requirement for the system being installed rather than working from memory, and record which figure was used.
Fall also has to be continuous. A recess that grades correctly in the middle but flattens at the corners, or that falls away from the waste at the entry, will pond. Ponding is the failure mode that shows up first, usually as efflorescence, mould or a persistent damp smell, and it is the one a certifier or an insurer will pick up on.
Depth is set by the waste, not by the tile
The depth of the recess is not a free choice. It is the sum of what has to fit inside it: the screed or graded substrate, the membrane, the adhesive bed and the tile, plus the waste assembly itself.
The waste is usually the binding constraint. A trap has a minimum depth, the outlet has a diameter, and the grate has a thickness and a footprint. If the recess is too shallow to accept the trap and still leave room for the graded substrate above it, the setout is wrong and no amount of care on site will fix it.
This is why waste selection should happen before the slab is poured or the floor is framed, not after. Where the recess has to be shallow, the options are generally a different waste with a lower profile, a raised perimeter to gain height, or a redesign of the floor structure. Thinning the screed below what the fall requires is not one of them.
Setdown sequence from slab to tile
- 1Confirm finished floor levelsEstablish the adjoining floor level and the depth of recess available before any concrete is poured or any floor joist is cut.
- 2Select the wasteMatch the trap depth, outlet size and grate to the recess depth and the tile module, and confirm it before the setout is fixed.
- 3Form the recessCast or frame the setdown to the depth the waste and the fall require, allowing for screed, membrane and adhesive build-up.
- 4Apply fall to the substrateGrade the screed or the structural fall so water runs to the waste outlet without ponding anywhere in the recess.
- 5Waterproof and terminateMembrane goes over the graded substrate and terminates at the height and detail the manufacturer requires, with the waste sealed to it.
- 6Tile to the setdownTile and adhesive are laid to the membrane, and the finished level inside the recess sits below the adjoining floor as designed.
Selecting the waste against the setdown
Waste selection is a drainage decision and a geometry decision at the same time. Work through the following for every wet area:
- Trap depth. The trap has to fit below the graded substrate and above the structure or the ceiling void. Confirm what is actually available, not what was assumed on the drawings.
- Outlet size and connection. The outlet has to connect to the drainage line without introducing a flat section or a backfall in the pipework.
- Grate type and footprint. A centre waste, a tile-insert grate and a linear waste all impose different fall patterns and different tile setouts.
- Tile module. The grate position has to work with the tile layout, otherwise the tiler is left cutting around the waste and the fall pattern fights the joints.
- Access. The waste has to remain serviceable after tiling, which affects the height it sits at relative to the finished floor.
Where a linear waste is used, the fall is typically formed to a channel rather than a point, and the recess has to be set out to suit. That changes the screed geometry and often the recess depth, so it is a decision to make early.
Setdowns in suspended floors versus slab on ground
The mechanics differ depending on what is underneath.
In a slab on ground, the recess is formed in the pour, either by boxing out or by casting to a stepped profile. The available depth is fixed once the concrete is placed, and cutting or grinding it later to gain height is slow, noisy and often not permitted.
In a suspended floor, the recess is usually created by dropping the floor structure or by framing a recess between joists. Here the constraint is often the depth of the joist and the position of the ceiling below, and the waste and its pipework have to fit in the void without compromising the structure.
In both cases, the waterproofing and tiling trades inherit whatever geometry they are given. The related article on slab edge thickness and setdown tolerances covers how those tolerances behave at the edge of a pour, which is where a recess usually starts to go wrong.
What to check before the waterproofer starts
The handover from the substrate trade to the waterproofer is the point where most setdown defects become visible. Run through the checks below on every wet area, and record anything that is out of tolerance rather than leaving it for the next trade to find.
Checks before the waterproofer arrives
- Finished floor level inside the recess sits below the adjoining floor by the margin you designed for.
- Fall to the waste is continuous, with no flat spots or backfall at the corners of the recess.
- Waste trap depth and outlet position suit the recess depth once screed, membrane and adhesive are allowed for.
- Recess sides are square and true so the membrane can turn up without bridging or tenting.
- Substrate is sound, dry and free of loose material, release agent or dust before membrane is applied.
- Any penetration through the recess, such as a tap body or a nib wall fixing, is sealed and detailed before tiling.
- Setdown dimensions and waste type are recorded on the drawings or a site instruction, not left verbal.
Two of those checks matter more than the rest. First, the fall: if water will not run to the waste on the bare substrate, it will not run once the membrane and tile are on. Second, the waste: if the trap does not fit, or the outlet is in the wrong place, the problem has to be solved before the membrane is laid, because afterwards it means demolition.
The mistake that costs the most. Tiling over a recess that ponds, or that leaves no room for the trap, converts a screed or plumbing fix into a full strip-out of membrane, screed, tiling and often the wall base. The builder carries the cost of the rectification, the delay to practical completion, and the reputational damage when the client is told the bathroom has to come out.
Worked example: a recess that was too shallow
A builder in western Sydney was renovating a first-floor bathroom in a brick veneer house. The existing floor was timber-framed, and the design called for a large tiled shower with a centre waste, set down below the adjoining floor level.
The setdown was framed by dropping the floor between the joists. The depth was worked out from the tile thickness and the adhesive bed, but the waste had not been selected at that point. When the plumber arrived, the trap specified by the client’s chosen tapware supplier would not fit under the graded screed without cutting into the ceiling void below, which was a finished room.
The options were to change the waste to a lower-profile unit, to raise the perimeter of the shower and lose the setdown, or to drop the ceiling. Each had a different cost and a different impact on the client. The builder priced them, put the options to the client in writing as a variation, and the client chose the low-profile waste, which allowed the setdown to stay.
The lesson is not that the builder got it wrong. The lesson is that the waste should have been locked in before the floor was cut, because the recess depth and the waste are one decision, not two.
Coordination with the trades that follow
The waterproofer and the tiler both need the setdown to be right, but they need different things from it. The waterproofer needs a sound, graded substrate with square, true upstands so the membrane can turn up without bridging or tenting. The tiler needs a fall pattern that suits the tile module and a waste position that can be cut cleanly.
Where a nib wall, a hob or a bath lip forms part of the setdown, the framing and the substrate behind it have to be set out at the same time, otherwise the membrane termination height and the tiling setout will not line up. Termination heights are set by the manufacturer’s system, so confirm the current requirement for the product being used rather than working from a previous job.
Penetrations through the recess — tap bodies, shower rail fixings, nib wall anchors — all need to be sealed and detailed before tiling. Each one is a potential path for water past the membrane, and each one is far cheaper to detail now than to chase later.
Documentation and compliance
Setdown geometry is not usually called out on a standard set of residential drawings, which is exactly why it goes wrong. The depth, the fall, the waste type and the finished floor level relationship should be documented on the drawings or in a written site instruction, and the trades should be working to the same figure.
Where the work is on a project that requires a BASIX certificate, the water and drainage commitments in that certificate form part of what has to be delivered. The NSW Planning Portal guidance on BASIX sets out how those commitments are recorded and assessed.
For builders working in areas subject to flooding, the ABCB guidance on construction of buildings in flood hazard areas deals with floor levels and drainage in a different context, but the principle of setting finished levels deliberately rather than by default applies in both.
Moisture behaviour inside the building envelope is covered in the ABCB Condensation in buildings handbook, which is worth reading alongside this topic because a wet area that ponds will show up first as condensation-related symptoms elsewhere in the building.
The point is that a setdown is a documented decision. If it is not written down, it will be re-decided on site by whoever is holding the tools that day, and that is how a bathroom ends up needing a strip-out.
Keeping the detail current
Standards, manufacturer systems and waste products all change. The fall figure, the termination height and the acceptable trap depth for a given product are things to confirm from the current source on every job, not to carry in your head from the last one.
For NSW builders, keeping that knowledge current is part of the continuing professional development obligation. The guide to how NSW builder CPD works explains what counts and how to record it, and the PointCPD course catalogue lists the wet area and waterproofing courses that cover this material in more depth. Builders who want to start from the beginning can review the PointCPD home page for NSW builder CPD courses.
None of that replaces checking the current requirement on the job. It just means you know what to check and why it matters.
Questions builders ask
How deep does a shower setdown need to be?
There is no single figure, because the depth is the sum of the graded substrate, the membrane, the adhesive bed, the tile and the waste assembly. The waste trap is usually the binding constraint, so select the waste first and set the recess depth from there. Confirm the current requirement for the specific system rather than working from a previous job.
Can the tiler create the fall with adhesive?
No. Tile adhesive is not applied to a controlled thickness and is not a grading material. The fall has to be formed in the structural substrate or in a screed laid before the membrane, and checked on the bare substrate before the waterproofer arrives.
What happens if the setdown is too shallow for the waste?
The options are generally a lower-profile waste, a raised perimeter that gives up the setdown, or a change to the floor structure such as dropping a ceiling. Thinning the screed below what the fall requires is not a valid fix. Price the options and put them to the client in writing as a variation before proceeding.
Does a bath need a setdown like a shower?
A bath needs the same containment principle: the wet zone has to be the low point so spillage drains back rather than running into the room. Whether that is achieved by a recess, a raised perimeter or a graded floor is a design decision, but the drainage outcome has to be the same. Set it out before the substrate is finished.
Where does the membrane terminate at a setdown?
The termination height and detail are set by the membrane manufacturer’s system, and they have to line up with the tiling setout and any nib wall or hob. Confirm the current requirement for the product being installed and make sure the framing and substrate are set out to suit it, because changing termination height after tiling is not practical.
How do I stop setdown problems recurring on the next job?
Document the depth, fall, waste type and finished floor level relationship on the drawings or in a written site instruction, and lock in the waste selection before the slab is poured or the floor is cut. Where the work needs a BASIX certificate, make sure the water and drainage commitments are reflected in that documentation.
Sources
- Construction of buildings in flood hazard areas · Australian Building Codes Board
- Construction of buildings in flood hazard areas · Australian Building Codes Board
- BASIX · NSW Planning Portal
- Condensation in buildings handbook · Australian Building Codes Board
Published 10 August 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.
