Key takeaways
- A setdown is only correct relative to the finished floor level it serves, so the slab setout has to be read against the architectural finishes schedule, not just the structural plan.
- Edge thickness at a door threshold is a live constraint on finished floor level because the tile bed, adhesive and tile have to fit inside the setdown without a step that trips or a cut that shows.
- The fall required in a shower recess eats into the available setdown, so a recess that is set down without allowing for the screed depth will force the tiler to build up outside the shower to keep the door line.
- Tolerance is cumulative: formwork, reinforcement chairs, pour level and screed all contribute, so a slab poured to the edge of its tolerance can leave no room for the fitout to recover.
- Recovering a shallow setdown after the pour means grinding, topping or rethinking the floor build-up, and that cost sits with whoever owns the setout, not with the tiler who found it.
A setdown is not a structural detail. It is a dimensional promise made on behalf of every trade that follows. The structural engineer sizes the slab for load and the architect draws the setdown for finishes, but the two documents are read by different people at different times, and the concrete does not care which one was right. By the time the tiler arrives, the setdown is a fixed number, and the fitout either fits inside it or it does not.
The cost of getting it wrong is asymmetric. Pouring a slab a few millimetres shallow costs nothing at the time; recovering that shortfall after the pour means grinding, topping, thicker screeds, or lifting the finished floor level and finding the door no longer clears. The trades who find the problem are not the trades who caused it, and on a residential job the builder is the one who owns the interface.
This article is about the setout decisions that sit between the slab and the finishes: how edge thickness and setdown depth relate to tile bed height, shower falls and door clearances, and what to check before the formwork is signed off.
What a setdown actually is, and what it is not
A setdown is a local reduction in the top of the structural slab, formed so that the floor build-up in a wet area or at a threshold finishes level with the adjacent floor. It is not the screed. It is not the tile bed. It is the void that the screed and tile will occupy, and its depth is set by the thickness of everything that goes into that void.
That distinction matters because setdown depth is measured from the top of the structural slab, while finished floor level is measured from a datum that the whole site shares. If the slab is poured high or low relative to that datum, the setdown depth is unaffected but the finished floor level moves. A slab poured high across the whole footprint can leave a setdown that is technically the right depth but sits above the floor it is supposed to match, and no amount of screeding will bring the two levels back together without a step.
The practical rule is that the setdown and the slab top are one decision, not two. You cannot set the slab top from the structural plan and the setdown from the architectural plan and expect them to agree. They have to be reconciled against a single datum before the formwork is fixed.
Edge thickness at thresholds is a fitout constraint
The slab edge at a door threshold is where the setdown meets the adjacent floor, and it is the point where the build-up has the least room to move. The edge has to be thick enough to carry the slab and the door frame, thin enough that the finished floor levels match, and consistent enough that the door leaf clears the floor across its whole width.
When a threshold is wrong, it usually shows up in one of three ways. The first is a step: the wet area floor finishes higher or lower than the adjacent floor, which is both a trip hazard and a visible defect. The second is a cut tile: the tiler has to reduce the tile bed to nothing at the door to meet the adjacent level, which leaves a thin, weak edge that cracks. The third is a door that will not swing: the finished floor level rises into the door clearance and the leaf drags or the frame has to be packed.
None of these are tiling problems. They are slab setout problems that present as tiling problems, and they are the reason the edge thickness at every threshold should be checked against the door schedule before the pour. If the door schedule is not final, that is a reason to hold the setout, not to pour and hope.
Reading a setdown before the pour
- 1Pull the finishes scheduleConfirm the finished floor level for each wet area and threshold before you set any formwork.
- 2Add up the build-upTile, adhesive, screed and any membrane have to fit inside the setdown without exceeding the door clearance.
- 3Check the fallThe screed at the waste is the deepest point, so the setdown has to be set from the waste, not the doorway.
- 4Confirm edge thicknessAt thresholds the slab edge has to carry the build-up and still leave the door leaf sitting correctly.
- 5Set out penetrationsWastes, floor wastes and door tracks need to land inside the setdown, not on the edge of it.
Shower falls and why the recess is not the doorway
The fall in a shower recess is created in the screed, and the screed has to sit inside the setdown. The deepest point of that screed is at the waste, not at the doorway, because the fall runs from the perimeter of the recess down to the waste. If the setdown is set from the doorway, the screed at the waste will be deeper than the setdown allows, and the tiler has two bad options: reduce the fall below the minimum the standard requires, or build up outside the shower to keep the door line.
Building up outside the shower is the common recovery, and it is the one that causes the most downstream grief. It raises the finished floor level in the bathroom, which then has to be reconciled with the hallway, the bedroom and the door threshold. It can also reduce the door clearance and change the relationship between the floor and the vanity or the bath. All of that is avoidable if the setdown is set from the waste, with the screed depth at the waste calculated first.
The waste position is therefore a setout input, not a plumbing afterthought. If the waste is moved after the slab is poured, the fall and the setdown depth are both affected, and the tiler inherits the difference.
Tolerance stacking: formwork, chairs, pour and screed
No single trade delivers a perfect dimension, and the setdown is the sum of several. Formwork moves when it is braced and again when concrete is placed. Reinforcement chairs compress or tip. The pour level varies across a slab even when the screed is run carefully. The screed itself has its own tolerance. Each of these is small; together they can consume the entire margin in a setdown that was designed to the minimum.
This is why designing a setdown to the exact build-up thickness is a mistake. The setdown needs a margin for the trades that follow, and that margin has to be explicit in the setout. If the build-up is tile plus adhesive plus screed, the setdown should be that sum plus an allowance for the slab and screed tolerances, not the sum itself.
On a job where the margin is tight, the answer is not to demand tighter tolerances from the concreters. It is to re-examine the build-up: a thinner tile, a different adhesive, a different screed method, or a change to the floor levels that gives the setdown more room. Those are design decisions, and they are cheapest to make before the pour.
Services, wastes and door tracks set out inside the setdown
A setdown is not just a void for screed. It is also where the waste, the floor waste, the shower screen track and sometimes the door track land. Each of these has a depth, and each of them has to fit within the setdown without projecting above the finished floor or sitting so close to the edge that the fixture cannot be fixed.
The floor waste is the most common problem. If the waste is set out on the edge of the setdown, the screed around it has to fall away in two directions at once, and the tiler ends up with a fall that is steeper on one side than the other. The waste should be positioned so the fall is even, which usually means it sits centrally in the recess and away from the door threshold.
Door tracks and shower screen tracks are similar. A track that lands on the edge of a setdown has no room for the screed to finish flush, so the track sits proud and the door or screen does not seal. These are setout decisions, and they belong on the slab plan alongside the structural reinforcement.
What to check before the formwork is signed off
The setout check is a short list, but it has to happen before the pour, because almost nothing on it can be recovered afterwards. The first check is that the finished floor level for every wet area and threshold is marked on a datum that the tiler, the joiner and the plumber can all read. The second is that the setdown depth is measured from the top of the structural slab, not from the top of the screed, and that the build-up thickness used to derive it matches the current finishes schedule.
The third is that the shower recess setdown is derived from the waste position, not the doorway, and that the screed depth at the waste has been calculated. The fourth is that the edge thickness at every threshold is checked against the door schedule, including the door leaf clearance. The fifth is that every penetration, waste and track is set out inside the setdown with enough room to set the fixture.
If any of those cannot be confirmed, the setout is not ready. Pouring and then discovering the problem is the most expensive sequence available.
Site checks before pouring a setdown
- Finished floor level marked on a datum that the tiler and joiner can both read.
- Setdown depth measured from the top of the structural slab, not from the top of the screed.
- Shower recess fall checked against the waste position, not the door opening.
- Door threshold edge thickness confirmed against the door schedule and frame setout.
- Penetrations and wastes set out inside the setdown with enough clearance to set the fixture.
- Formwork checked for level across the setdown, not just at the corners.
- Reinforcement cover confirmed so the edge does not spall when the formwork is stripped.
Worked example: a bathroom setdown that left the tiler no room
A builder in western Sydney was constructing a single-storey dwelling with two bathrooms and a laundry. The structural plan showed a setdown at each wet area, and the architectural plan showed a tiled finish with a screed bed and a recessed shower. The setdown was formed to the depth shown on the architectural plan, measured from the top of the slab.
The slab was poured and finished within what everyone considered normal tolerance. When the tiler arrived, he found that the shower recess setdown was shallower at the waste than the screed depth required to achieve the fall, because the waste had been set out close to the door threshold and the fall had to run back towards the doorway. To achieve the fall, he would have had to build up outside the shower by more than the door threshold could accommodate without raising the bathroom floor above the hallway.
The recovery was a grind of the recess to gain depth, a topping screed in the bathroom, and a change to the door undercut. The grind and the topping were both variations, and the builder carried them because the setout had been taken from the wrong reference point. The lesson is not that the tiler should have found a way; it is that the setdown should have been set from the waste, with the screed depth calculated before the formwork was fixed.
How this connects to the rest of the slab and the site
Setdowns sit within a broader slab setout that includes edge thickness, reinforcement cover, and the relationship between the slab and the footings that support it. If the footings are out of level, the slab top moves, and the setdown moves with it. The PointCPD article on strip footings and pad footings in residential NSW covers the setout decisions that sit underneath this one, and the article on waffle raft slab defects covers the defects that show up when the slab itself is not right.
There is also a safety dimension to the pour itself. Concrete pumping and placement carry their own risks, and the Safe Work Australia guidance on concrete pumping sets out the controls that apply when a boom or line pump is on site. Separately, the model code of practice for managing the risk of falls in housing construction is relevant to anyone working at the slab edge or on formwork before the pour. Those are not setout issues, but they are part of the same day’s work, and the PointCPD article on falls from height and roof plans deals with the planning side of working at height.
Before any excavation or penetration work associated with the setout, the site also needs its service locations confirmed through Before You Dig Australia. A setdown that is set out without checking for services can put a waste or a penetration into a line that nobody knew was there.
Where to go for the current requirements
The specific tolerances for slab setout and the minimum fall in a shower recess are set by the relevant Australian Standard and by the NCC, and they change from time to time. This article deliberately does not restate them, because a figure quoted from memory is worse than no figure at all. If you need the current number, check the standard or the NCC edition that applies to your project, and check the manufacturer’s instructions for the tile, adhesive and waterproofing system you are using, because those can be more restrictive than the standard.
The Cement Concrete and Aggregates Australia publications are a useful reference for concrete practice and for the way slabs are specified and finished. They are not a substitute for the project documents, but they help you understand why a specification is written the way it is.
For NSW builders, the CPD system requires you to keep your knowledge current, and the guide to how NSW builder CPD works explains the categories and the record-keeping. The PointCPD course catalogue includes material on slab and footing practice, and the PointCPD home page is the starting point for the NSW builder CPD courses.
The commercial case for getting the setout right
A setdown that is wrong is rarely a large defect. It is a few millimetres in the wrong place, and it does not affect the structure. But it surfaces during fitout, when the programme is tight and the trades are stacked, and the recovery options all involve either grinding, topping, or changing the finishes. Each of those is a variation, and the question of who pays turns on whether the setout was correct against the documents.
The builder who can show a documented setout check, a datum that all trades worked to, and a reconciliation between the structural and architectural plans is in a much stronger position than one who cannot. That is not just a commercial defence; it is the difference between a fitout that runs to programme and one that stalls while someone decides who is paying for the grind.
The time to get it right is before the formwork is signed off. After the pour, the only question is how much it costs to fix.
Questions builders ask
What is a slab setdown and how is it different from a screed?
A setdown is a local reduction in the top of the structural slab, formed so that the floor build-up in a wet area or at a threshold finishes level with the adjacent floor. The screed is the material placed inside that setdown to create the fall and the bed for the tiles. The setdown is the void; the screed fills it.
How deep should a shower recess setdown be?
The depth is set by the thickness of the screed required to achieve the fall, plus the tile and adhesive, plus an allowance for slab and screed tolerances. It is not a single number, because it depends on the waste position and the fall required. Check the current standard and the project documents for the minimum fall that applies.
Why does the setdown need to be set from the waste rather than the doorway?
The screed is deepest at the waste because the fall runs from the perimeter down to the waste. If the setdown is set from the doorway, the screed at the waste may be deeper than the setdown allows, which forces the tiler to either reduce the fall or build up outside the shower. Setting the setdown from the waste keeps the fall and the door threshold consistent.
What happens if the slab is poured high and the setdown is too shallow?
The finished floor level in the wet area rises, which can create a step at the threshold, reduce the door clearance, and change the relationship between the floor and the fixtures. Recovery options include grinding the slab, applying a topping screed, or changing the floor build-up. All of them are more expensive after the pour than correcting the setout before it.
Who pays for the cost of correcting a setdown that is wrong?
It depends on whether the setout was correct against the documents and whether the builder can show a documented check. If the setdown was formed to the wrong reference point, the builder generally carries the cost, because the setout is the builder’s responsibility. If the documents themselves were inconsistent, the position is more complex and depends on the contract.
Where can I find the current tolerance and fall requirements for slabs?
The requirements are set by the relevant Australian Standard and by the NCC edition that applies to your project. Manufacturer instructions for the tile, adhesive and waterproofing system can also be more restrictive than the standard. Check the current documents rather than relying on a figure from memory or from an older project.
Sources
- Concrete pumping · Safe Work Australia
- Before You Dig Australia · BYDA
- Cement Concrete and Aggregates Australia · CCAA
- Managing the risk of falls in housing construction: code of practice · Safe Work Australia
Published 26 June 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.
