Rooftop pools: what does the building structure need?

Planning a pool on a roof, podium or suspended slab? Get a quote or call 1300 128 972, and send the architectural plans, the building's structural drawings and the pool layout with its water depth.

How much load does a rooftop pool put on the building?

A rooftop pool puts about 1 tonne on every square metre of slab for each metre of water depth, before the weight of the shell, screed, tiles and people. The U.S. Geological Survey gives the density of water as roughly 1 gram per cubic centimetre, which is 1,000 kg per cubic metre. Multiplied by standard gravity, 9.80665 m/s² (NIST), each metre of depth adds about 9.8 kPa.

Water depth	Mass of water per m² of slab	Pressure on the slab from the water alone
0.5 m	about 500 kg	about 4.9 kPa
1.0 m	about 1,000 kg	about 9.8 kPa
1.5 m	about 1,500 kg	about 14.7 kPa
2.0 m	about 2,000 kg	about 19.6 kPa

For scale, explanatory information in NCC 2019 Volume Two said a 2 kPa imposed load "is commensurate with domestic and residential activities" for decks and balconies attached to houses. It added that 2 kPa is not appropriate where a deck or balcony supports spa or bathing pools, and that framing for higher loads must be designed by a professional engineer or other appropriately qualified person. That note is from a superseded edition and about decks, but water alone at 1.5 m deep is more than seven times 2 kPa.

The National Construction Code (NCC) 2025 Volume One, clause B1P1, lists the actions a structure must be designed for. For a rooftop pool, the relevant ones include:

• permanent actions (dead loads) from the shell and finishes;
• liquid pressure action from the water;
• wind action and earthquake action;
• time dependent effects, including creep and shrinkage;
• construction activity actions.

Do waves and sloshing load a rooftop pool?

No Australian source sets a separate sloshing load, but water high in a building may move as the building sways. NCC 2025 clause B1D3 already requires wind and earthquake actions, determined to AS/NZS 1170.2 and AS 1170.4.

A 2023 study in the journal Wind and Structures, by researchers in China (an overseas study), ran wind tunnel tests on an irregular hotel building, then used a numerical model calibrated to those tests to calculate that a pool on its top "has acceptable damping effect" and could be designed as a tuned liquid damper (TLD) to reduce the building's wind-induced vibration. The study looked at the building's motion, not at the pool walls, but a pool can only damp a building's movement if its water moves, so water high in a building may not stay still. The engineer checks what that means for the walls, edges and any overflow.

Which concrete standards apply to a rooftop pool shell?

SPASA's guide names AS 2783:2025 as the industry-accepted standard for concrete pools within its scope, and AS 3600 or AS 3735 where a broader assessment is needed. AS 3735 sets serviceability, durability, joint and waterstop, and liquid-tightness testing requirements for concrete structures that retain liquids.

AS 3735-2001, Concrete structures for retaining liquids, is the Australian Standard for reinforced or prestressed concrete structures that hold liquids at ambient temperature. Its preface says that for these structures it supplements and takes precedence over AS 3600, Concrete structures. Its sections cover:

• loads and load combinations, including combinations for serviceability;
• design for serviceability and strength, for reinforced and prestressed concrete;
• durability, including exposure classification and cover to reinforcement;
• joints, waterstops, joint fillers and sealants;
• testing for liquid-tightness.

A rooftop pool shell sits on a slab that deflects under the water, and NCC clause B1P1 lists time dependent effects, including creep and shrinkage, among the actions to design for. The engineer checks that the slab's deflection and the shell's cracking stay within the serviceability limits of the standards that apply, for the actual span and exposure. Our guide to why concrete pools crack covers cracking in pool shells more generally.

SPASA's industry guide sets out which standard to start from:

Standard	What it covers	When SPASA's guide points to it
AS 2783:2025	Use of reinforced concrete for small swimming pools	The industry-accepted standard for concrete pools within its scope
AS 3735-2001	Concrete structures retaining liquids	Where a broader structural assessment is needed
AS 3600	Concrete structures generally	Where a broader structural assessment is needed
AS 1838 and AS 1839	Pre-moulded fibreglass shells: design and fabrication, then installation	For fibreglass pools

How is a rooftop pool waterproofed against the building?

A rooftop pool relies on two separate lines of defence: a watertight shell, and the building's own waterproofing membrane under and around it. The NCC requires a waterproofing membrane on a roof, balcony, podium or similar horizontal surface, with materials complying with AS 4654.1 and design and installation to AS 4654.2. Joints in that surface are controlled too:

NCC rule	NCC 2022 Volume One	NCC 2025 Volume One
Membrane on a roof, balcony or podium, to AS 4654.1 and AS 4654.2	F1D5	F1D7
Exposed joints protected to Section 2.9 of AS 4654.2	F1D4	F1D6
Exposed joints not beneath or through a planter box, water feature or similar	F1D4	F1D6
Exposed joints on the ridge line or high point of the substrate	Suggested in explanatory information, where possible	F1D6

The NCC's notes define an exposed joint as a construction, control, expansion, contraction or movement joint. NCC 2022's explanatory information suggests considering extra measures where a joint moves more than 10 mm, such as a hob at least 50 mm high and a discontinuous membrane. The rule names planter boxes and water features, and a pool on a podium raises the same question, so it helps to set out the building's movement joints before the pool's position is fixed. Inside the shell, AS 3735 deals with its own joints and waterstops.

Who designs what: the pool engineer or the building engineer?

No standard or regulation fixes the split. The NSW Government's guidance for regulated buildings says design work "must not occur in isolation" from other design practitioners' work, so agree in writing who owns each part before drawings start. One way to split it:

Item	Suggested owner (agree in writing)
The roof slab, transfer beams, columns and footings carrying the pool	The building's structural engineer, using loads from the pool engineer
The pool shell, its reinforcement, joints and waterstops	The pool engineer
The membrane under and around the pool	The waterproofing designer, coordinated with both engineers
Movement joints between the shell and the building	Agreed between both engineers and the waterproofing designer
Plant room, balance tank and pipe loads	Whoever designs the slab they sit on

Before work starts, settle the practical questions: how concrete and steel reach the roof, where materials are stacked on the slab, what propping stays in place, when the membrane goes down and how it is protected, and when the shell gets its liquid-tightness test.

Rooftop pool rules in NSW, Victoria, Queensland and WA

A rooftop pool needs the same approvals as any pool, and on an apartment building it also falls under the rules for that building. NSW and Queensland adopt NCC 2025 on 1 May 2027; Victoria and Western Australia adopted it on 1 May 2026 (ABCB).

State	What the official source says
NSW	For class 2, 3 and 9c buildings, building structure and waterproofing are building elements. Their regulated designs must be declared by a registered design practitioner and lodged on the NSW Planning Portal before related work starts (NSW Government).
Victoria	A building permit is needed for a pool or spa deeper than 300 mm, including above-ground pools and spas (Consumer Affairs Victoria).
Queensland	Building approval from your council or a private certifier, with architectural plans and engineering specifications (QBCC).
Western Australia	"All swimming pools and spas need building approval" (Building and Energy).

SPASA notes a pool must also meet the NCC's requirements for safety barriers. Our guide to pool building permits covers the approval pathway in NSW, Victoria, Queensland and WA.

When to call a structural engineer

Call a structural engineer before the pool's size and position are fixed if any of these apply:

• the pool will sit on a roof, podium, balcony or any suspended slab;
• you are adding a pool to an existing building;
• the pool has a vanishing edge, glass wall or overflow to a balance tank;
• the building's movement joints run near the planned pool.

Our pool structural engineering service covers the shell and its supports, and the pool engineering plans page lists the drawings and calculations you receive. Our page on indoor pools has a section on suspended and podium pools, including deflection and movement joints between pool and building, and pool builders can start at for pool builders.