Building components · Substructure & Ground
Pool Tank Wall
Explains the tank wall as an element loaded in opposite directions at different times, distinct from a retaining wall, from a basement wall and from the waterproofing applied to it.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a tank wall is
A pool tank wall is the vertical element that contains the water of a pool and, where the pool is set into the ground, holds back the ground outside it. With the tank floor it forms the shell: a water-retaining structure in which continuity matters as much as strength, because a tank that cracks loses water whether or not it is still standing perfectly well.
What makes it distinctive is that its two faces are loaded in opposite directions and rarely at the same moment. Full, the wall is pushed outwards by the water it contains. Empty, it is pushed inwards by the ground and, where groundwater is present, pressed and lifted by that as well. A wall detailed for only one of those conditions is detailed for half its life, which is why emptying a pool is commonly a question for the engineer who designed the tank rather than a routine maintenance decision.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a retaining stem. A retaining stem holds back ground with air on the other side and is loaded in one direction; a tank wall has water on one face and ground on the other and is loaded from both, in alternation.
- It is not a basement wall. A basement wall exists to keep water out of an occupied space, and its failure shows as damp inside; a tank wall exists to keep water in, and its failure shows as water going missing.
- It is not a waterproofing layer. Barrier waterproofing and integral water-resisting concrete are published system entries describing how water is kept where it belongs; the tank wall is the structural element that such an approach is applied to, or designed into.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- pool wall
- basin wall
- pool shell wall
- tank side
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The ground and groundwater conditions outside it, which govern what it carries when the pool is empty and whether an empty tank can be lifted.
- Whether it has been designed as a water-retaining structure, since containing water is a different design case from resisting ground.
- The continuity of the tank at every construction joint, movement joint and junction with the floor, because those are where water-retaining structures lose water.
- Every penetration through it — inlets, outlets, lighting, pipework — each being a hole through a surface whose job is to have none.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The wall has water against one face continuously and ground moisture against the other, so it is wet from both sides for the whole of its life and neither face is readily inspected.
The wall is pushed outwards by water and inwards by ground, and for the ground side the empty condition is commonly the governing one.
Pool water is treated water, and both it and the ground outside act continuously on a structure that cannot easily be seen from either side.
A water-retaining structure has to accommodate movement without opening a path for water, which is why joints in a tank are a designed feature rather than an incident of how the concrete was poured.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Clarifications
Commonly misunderstood
- That a pool can be emptied whenever it is convenient. An empty tank is loaded differently from a full one, and where groundwater is present an empty tank can be pushed or lifted by it.
- That a leak is a lining problem. Water loss from a pool can originate in the shell, in a joint, at a penetration or in the pipework, and establishing which is investigative work.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Has this been designed as a water-retaining structure, and by whom?
- What are the groundwater conditions outside the tank, and what does the design assume about the pool being emptied?
- How are the joints between wall and floor, and between successive pours, formed and sealed?
- How does each penetration through the wall maintain the continuity of the tank?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- This entry describes a position. It states no thickness, reinforcement, water pressure, joint detail or waterproofing specification, and none can be inferred from it.
- Pool structures are designed by qualified engineers for their own ground and groundwater conditions; emptying, altering or repairing one is not something a reference entry can advise on.
Substructure & Ground Elements
The prepared surfaces, layers and buried members between undisturbed ground and the first structure above it.
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