Shower trays · Drainage · Project coordination
Check the entire water path before approving the tray and waste.
Separate incoming flow, the waste test condition, pipe design and the installed result. Pass a usable decision record between design, purchasing, installation and maintenance.
Short answer: Approve the shower outlets, waste fitting, pipe route and tray as one hydraulic chain. The design input is the maximum flow that can actually enter the tray. The system limit is not the largest number on a waste datasheet; it is the weakest verified part of the complete installed route.
A 90 mm waste hole, a 40 mm pipe and a “high-flow” product name are dimensions and descriptions—not a drainage budget.
Start with four different numbers
| Number | What it describes | What it does not prove |
|---|---|---|
| Outlet flow | Water delivered by the showerhead, hand shower, body jets or filler at stated pressure and operating mode | That two outlets cannot run together, or that site pressure produces the catalogue value |
| Waste-fitting capacity | Flow through a named waste under its stated test condition, often including a stated water head | Capacity of the connected branch pipe or a partially obstructed in-service assembly |
| Pipework design capacity | What the applicable plumbing design allows for the selected diameter, gradient, length, bends and ventilation | That the tray-to-waste joint is sealed or the strainer remains clean |
| Installed test result | Observed behaviour of the assembled tray, waste and pipe route under a controlled flow | Every future condition unless the test flow, duration and maintenance state are recorded |
Keep these values separate. Converting them to the same unit helps comparison, but it does not make their test conditions equivalent.
Calculate the incoming design flow first
List every outlet that can discharge into the tray. Record the exact model, spray mode, catalogue pressure and maximum flow. Then use the valve or diverter logic to decide which combinations are physically possible.
The Hansgrohe Rainfinity 26227000, for example, publishes 8.1 L/min at 3 bar. That equals 0.135 L/s. The number is useful only for that model and condition; it is not a generic rainfall-shower flow.
For a hypothetical system where an 18 L/min overhead shower and a 10 L/min hand shower can operate together, the incoming design flow is 28 L/min, or approximately 0.467 L/s. If the diverter prevents simultaneous use, adding the two values would overstate the design input. Confirm the control logic instead of guessing.
Use a Worked Calculation Without Turning It Into Approval
| Illustrative input | Calculation / meaning | Decision still open |
|---|---|---|
| Overhead 18 L/min + hand shower 10 L/min, if simultaneous | 18 + 10 = 28 L/min; 28 ÷ 60 ≈ 0.467 L/s. These are hypothetical outlet values. | Confirm the actual valve logic and maximum delivered flow. |
| Waste example: 0.62 L/s at a stated 15 mm head | 0.62 × 60 = 37.2 L/min at the declared product condition. | Does the allowed tray water depth and exact assembled waste match that condition? |
| Connected branch and installed assembly | No pipe capacity is calculated from outlet diameter alone. | Complete the local pipe design and final-cover flow / leak test. |
The difference between the two catalogue numbers is only a screening observation. It is not a quantified maintenance allowance, overflow guarantee or substitute for downstream design.
Read the waste rating with its water head
A waste often needs water above the grate to achieve its declared capacity. The Viega Tempoplex 6965.1 product data publishes 0.62 L/s at a 15 mm accumulation height for model 6965.1, article 801 793, with a vertical DN 40/50 outlet. The listed functional unit excludes the cover cap; confirm the exact cover and installed assembly separately. That is a product-specific test result—not permission to assume 0.62 L/s with zero water depth, a different cover, a restricted adaptor or an adverse pipe route.
Converting both figures to L/min makes the units comparable, but a ratio such as 0.62 ÷ 0.135 is not a verified installed-system safety factor. The waste figure belongs to a stated water head and configuration; the showerhead figure belongs to a stated supply pressure. Complete the pipe review and installed test before approval.
Use one worksheet, not one headline number
| Worksheet field | Record | Hold point |
|---|---|---|
| Operating combinations | Outlet models, spray modes, diverter logic and site supply condition | No assumed “one outlet only” rule |
| Incoming design flow | Maximum permitted simultaneous flow in L/min and L/s | Convert units and preserve source pressure |
| Waste test result | Exact part number, cover, outlet, test head and declared capacity | No borrowing a value from a related model |
| Tray geometry | Falls, drain recess, perimeter landing and threshold relationship | Do not treat available storage as normal operating capacity |
| Pipe route | Diameter, gradient, developed length, bends, trap, venting and shared branch | Competent plumbing review against destination rules |
| Maintenance state | Removable strainer, hair capture, clean-out and service access | Define who can restore flow without removing the tray |
| Commissioning | Measured test flow, duration, water depth, ponding and leak observations | Record before tiling, panels or ceilings conceal the route |
Do not translate regional rules into false equivalence
Europe and the United Kingdom
BS EN 274-1 is the product framework for sanitary-appliance waste fittings, while BS EN 14527 addresses domestic shower trays. Neither removes the need to coordinate the building pipework and exact installation.
United States — an IPC example
The 2024 International Plumbing Code requires shower waste outlets of at least 1½ inches (38 mm) and routes waste fittings to ASME A112.18.2/CSA B125.2. The diameter requirement is not a product flow-capacity certificate and local adoption must be checked. For a Canadian project, confirm the applicable provincial or territorial requirements; this U.S. model-code example is not a Canadian approval.
Australia
NCC 2022 Volume Three, Part C1 contains a system-based pipe-sizing verification method using discharge units, usage factors and probable simultaneous wastewater flow. Its method and system assumptions must be applied together. A discharge-unit entry is not measured showerhead flow and is not a product rating for a tray waste. Confirm the edition and state or territory provisions adopted for the project.
A field test that produces useful evidence
- Verify the tray is supported and level according to its current instructions.
- Confirm that all accessible waste joints are visible and dry before starting.
- Measure the delivered flow using a suitable calibrated flow instrument or a timed-volume method; record outlet combination, pressure condition and water temperature where relevant.
- Run the agreed maximum operating combination for the specified duration.
- Record the stable water depth near the waste, any threshold approach, unintended ponding and the first sign of restriction.
- Inspect all accessible joints during the test and again after drainage stops.
- Repeat after fitting the final strainer or cover; a test with the cover removed is not the finished configuration.
- Keep photographs, video, measurements, product identities and the pass/fail rule in the handover file.
Do not create a clog by adding fibres, soap or debris unless a controlled test method specifically requires it. Maintenance allowance should be addressed through the project specification, access strategy and supplier evidence—not an improvised site obstruction.
Illustrative Case: A Changed Outlet Schedule Reopens the Drainage Decision
A buyer sees an 8.1 L/min showerhead and a waste rated at 0.62 L/s and approves the combination immediately. On site, the designer changes to a multi-outlet valve, a compact adaptor is added under the tray and the branch crosses several bends before reaching the stack. The original comparison no longer describes the installed system.
The correct response is not to blame the tray or increase the waste-hole diameter blindly. Reissue the outlet schedule, verify simultaneous flow, review the exact waste and pipe route, then commission the final assembly at the agreed operating condition.
Pass One Evidence Pack to the Next Owner
Keep the model and drawing revision attached to each decision, and identify who closes the remaining question.
| Handoff | Send | Close before release |
|---|---|---|
| Designer → plumber | Confirm outlet models, simultaneous modes, site supply and the branch route. | The pipe design and waste rating describe the same operating condition. |
| Plumber → buyer | List the exact waste, cover, seals, connector and permitted tray interface. | No substitute is treated as equivalent on diameter alone. |
| Installer → quality | Pass on recorded flow, duration, water level, joint inspection and final-cover condition. | Concealment is released against a recorded result. |
| Quality → facilities | Identify the service parts, cleaning route and access limitations. | Routine flow restoration does not rely on removing the tray. |
Primary References and Their Application
- European/UK product frameworks: BSI — BS EN 274-1, Waste fittings for sanitary appliances and BSI — BS EN 14527, Shower trays for domestic purposes.
- Waste product example: Viega Tempoplex 6965.1 product data. The 0.62 L/s example belongs to model 6965.1, article 801 793, at 15 mm accumulation height; identify the cover and assembled test configuration.
- Shower outlet example: Hansgrohe Rainfinity 26227000 technical page. The cited 8.1 L/min maximum is stated at 3 bar for the named model.
- North American code example: 2024 International Plumbing Code, Sections 421.3 and 421.3.1. Confirm the edition adopted by the project jurisdiction.
- Australian pipe-sizing framework: NCC 2022 Volume Three, Part C1. Its discharge units, usage factors and pipe-sizing method belong to the stated system context; they are not a universal waste-product capacity.
Request a drainage-budget review
Send the outlet schedule and permitted operating combinations, flow data with pressure, exact tray and waste drawings, pipe route and service-access proposal. Mark the values that are measured, declared or still unverified, and identify who will close the pipe-design and installed-test decisions.
Review the shower drainage budget