Swimming Pool Design and Structure: An Engineer's Guide

Swimming pool design is usually discussed in terms of shape, tiles and lighting, but a pool is first a structure. It is a concrete tank holding tens of tonnes of water, set into or onto the ground or a building, that must stay watertight for decades while chemicals, temperature changes and groundwater work on it. Most pool problems we see, leaks, cracks, tiles debonding, movement at the coping, trace back to decisions about structure and waterproofing rather than finishes.

This article explains how a pool is designed from the structure outward: the shell, the loads it carries, groundwater, waterproofing, circulation and drainage, and the approvals that apply in Singapore.

Types of pool structure

In-ground reinforced concrete pools

The most common form for permanent residential and commercial pools is a cast-in-place reinforced concrete shell, either poured in formwork or sprayed (sprayed concrete is often called shotcrete or gunite). Concrete allows almost any shape, integrates steps, benches and overflow channels, and carries a tiled or rendered finish.

Elevated and rooftop pools

Pools on podiums, roofs and upper floors are carried by the building’s frame. The pool shell becomes part of the structure, and its weight, which is considerable, must be carried down through beams, columns and foundations. These pools have the least margin for error, because a leak goes straight into occupied space below.

Other systems

Prefabricated shells, steel or panel systems with liners, and fibreglass pools are used in some markets. They have their own design rules, but the principles of support, drainage and groundwater still apply.

Swimming pool design loads on the shell

A pool must be designed for several load cases, and the worst case is not always the full pool.

Water pressure. Pressure increases with depth, at roughly 10 kN/m² for every metre of water. The walls act like retaining walls loaded from the inside, and the floor carries the full weight of water.
Soil pressure. When the pool is empty, the surrounding soil pushes inward on the walls. Saturated soil after heavy rain pushes harder.
Surcharge. Paving, decks, structures and vehicles near the pool edge add load to the soil and therefore to the walls.
Groundwater uplift. If the water table is high, an empty pool can be pushed upward like a boat. This is the case most often overlooked.
Self-weight and finishes, including copings and any features.

Elevated pools add the load of the full tank to the supporting floor, along with dynamic effects from people and, in some cases, sloshing. See our guide to types of structural loads for how these are combined in design.

Groundwater, soil and foundations

Ground conditions decide how an in-ground pool is founded. A soil investigation, even a modest one for a house pool, tells the engineer the soil type, its bearing capacity and the groundwater level.

Where groundwater is high, flotation must be prevented. Common measures include making the shell heavy enough to resist uplift, extending the base slab beyond the walls so the soil above helps hold it down, providing tension piles, or installing hydrostatic relief valves that allow groundwater into the pool if it is emptied. The maintenance manual should tell owners never to empty the pool without checking groundwater conditions.

On soft or variable ground, a pool may need piles to control settlement. Uneven settlement is particularly damaging, because it cracks the shell and tilts the waterline relative to the coping, which is easy to see and hard to correct.

Making the shell watertight

A pool is a water-retaining structure, and its concrete is designed to stricter crack-control rules than ordinary building elements. In Singapore, structural design follows the Eurocodes, and Eurocode 2 Part 3 addresses liquid-retaining structures. In practice, watertightness comes from several measures working together:

Dense, well-compacted concrete with an appropriate mix, adequate cover to the reinforcement and good curing.
Crack control through reinforcement detailing, joint layout and limiting restraint during early shrinkage.
Waterstops at construction joints, and careful detailing at pipe penetrations, lights and fittings.
A waterproofing system, typically cementitious or membrane-based, applied inside the shell beneath the tile bed; for elevated pools, often a secondary system below as well.
Testing. The shell is filled and monitored for water loss before finishes are applied.

Our article on waterproofing in construction compares the main systems. Chemical attack from pool water and cleaning agents, and chlorides in the case of saltwater systems, also affect the choice of finishes and the protection of reinforcement.

Circulation, filtration and drainage

The hydraulic system keeps the water clean and balanced. Water is drawn off through skimmers or an overflow channel and main drains, filtered and treated in a plant room, and returned through inlets positioned to avoid dead spots. Overflow pools, including infinity edges, use a balance tank to hold the water displaced by swimmers and the volume in transit. Our article on the infinity pool explains this arrangement.

Suction outlets must be designed to prevent entrapment, with anti-vortex covers and multiple outlets so that no single drain can trap a swimmer. The plant room needs ventilation, drainage, safe chemical storage and access for maintenance.

The pool surround must drain away from the water and from the house. Backwash water and the pool’s emptying route need a proper discharge point; pool water should not be released into surface drains or onto neighbouring land without considering what the authorities permit.

Approvals and regulation in Singapore

Several frameworks may apply, depending on the property:

Planning. URA’s landed housing guidelines set out where pools may be located relative to boundaries and road reserves, and treat sunken and raised pools differently. Check the current handbook for your house type.
Structure. Pool structures, and any pool on or within a building, require structural design by a Professional Engineer and building plan approval from BCA where applicable. Adding a pool to an existing building is addition and alteration work.
Water quality. Shared pools in condominiums, clubs and hotels are licensable aquatic facilities under NEA’s Environmental Public Health (Licensable Aquatic Facilities) Regulations 2021, with water quality testing and reporting duties. A private pool at a single landed house is generally outside that licensing regime, but still needs proper treatment.
Strata. Works in condominiums need management corporation approval.

Frequently asked questions

What is the most important part of swimming pool design?

Structurally, the shell’s watertightness and its stability under every load case, full, empty and with high groundwater, matter most. A beautifully finished pool on a cracked or floating shell will leak and move, and correcting it means draining and reconstructing much of the work.

Why can emptying a pool be dangerous?

If groundwater around the pool is high, an empty shell can be pushed upward by buoyancy, cracking the structure and lifting it out of level. Pools in such conditions are designed with extra weight, anchorage or relief valves, and should not be emptied without checking conditions.

Does a rooftop pool need special design?

Yes. The weight of the water and shell must be carried by the building frame and foundations, and a leak affects occupied space below. Elevated pools typically have more robust waterproofing, careful detailing of joints and penetrations, and accessible areas for inspection.

Do I need a Professional Engineer for a house pool in Singapore?

Generally yes. A pool is a structure, and structural works in Singapore require design and endorsement by a Professional Engineer, with building plan approval where required. Planning guidelines on pool location for landed homes also apply.

How is a concrete pool tested for leaks?

Before tiling, the shell is filled with water and the level is monitored over a period while allowing for evaporation. Any significant loss indicates a leak that must be found and repaired before waterproofing and finishes are applied.

Planning a new pool or adding one to an existing building? Talk to our consultancy or get in touch.