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The photographers Wildash own the copyright of these images of the Embassy Gardens Sky Pool


Pool tanks

The purpose of the pool tank structure is to support and contain the water within whilst preventing water loss or ingress.

The pool surround must also be designed to prevent water loss or ingress. This can be achieved by adopting a method of construction which is inherently watertight or derives water retention from an applied finish. Sport England guidance states that a waterproof membrane should generally not be used between the concrete structure and the tiling, as they can be the cause of subsequent failure if there is shocking of the pool tank, through emptying or heating.

The guidance assumes that the concrete structure is liquid retaining. It is to be noted that many successful pool tanks have been constructed using waterproof membrane technology.

Key elements to consider in your design
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All swimming pools must be emptied for maintenance at some point.  If the ground water table is high, pools of lightweight construction and pools that rely on an applied water retaining lining can be at risk of water ingress, liner detachment or floatation.  Pools constructed when ground water levels are low are particularly susceptible.

Where there is the risk of a high-water table the structural engineer will need to address the risk of floatation; approaches include anchoring the pool down by mass or tied into other structure, and/or hydrostatic relief valves.

Pool tanks will normally incorporate the following elements:

  • On a deck level pool, dedicated surface water removal channels around the perimeter of the pool tank or sometimes called transfer channels; alternatively, skimmer boxes at discreet locations, though this is more appropriate to domestic installations
  • Water treatment inlet and outlet fittings
  • Pool tank access via walk-in steps or via vertical ladders with grab rails
  • A separate dedicated balance tank, ideally installed adjacent to the pool underneath the pool surround; balance tanks are provided with access manways for maintenance/cleaning
  • Drowning detection systems
  • Movable pool structures
  • Underwater lights.
  • Other construction options, not listed below, include reinforced blockwork with a waterproof membrane, glass reinforced polyester (GRP) and numerous other novel options; normally found on smaller domestic installations.

Transparent acrylic panels are increasingly being used in pool tank construction, from small windows to complete walls of pools.  Our project, The Sky Pool at Embassy Gardens, London is a fantastic ground-breaking example of this method of construction.

Every pool tank presents a risk of leakage.

Where a pool tank is in the ground in a back garden, the risk from leakage is generally low.  However, if the pool tank is in an elevated location with accommodation below, then the potential risks are much higher.  In such situations a risk reduction strategy should be addressed, to minimise the risk.  There are many things that can be considered, including a box in box approach, whereby an outer box is provided to contain and pass to drain any leakage that may occur from the inner pool tank.

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Swimming pool tanks and balance tanks can be formed with water retaining reinforced concrete to BS EN 1992-3 Type 2; this method of construction is inherently watertight.

An alternative is to use non-water retaining reinforced concrete to BS EN 1991-1-1 with an applied waterproofing membrane.  Reinforced concrete is normally specified by the structural engineer.  The concrete is either formed using shutters or is sprayed using say Gunnite or Shotcrete.

Stainless Steel
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There are generally two stainless steel options.

The first option is for an all welded stainless steel tank where the steel remains exposed to the bathers, so hence a grey metallic finish, normally brush finished; this is often sold as being a most hygienic solution as there will not be any cracks or crevices that can harbour bugs; this type of tank is widely used on the continent.

The second option is where the stainless-steel tank is primarily there to provide the structure, and the waterproofing is provided by a loose laid liner (one supplier has the liner bonded to the walls).  Key benefits of stainless-steel tanks are offsite build, accuracy, speed of construction and lower embodied carbon.

Regulations, Standards and Guidelines
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The following documents are relevant to the design of a pool tank and the surrounds:

  • BS EN 15288-1: Swimming Pools Part 1 – Safety requirements for design
  • BS EN 15288-2: Swimming Pools Part 2 – Safety requirements for operation
  • BS EN 13451-1: Swimming Pool Equipment – General safety requirements and test methods
  • BS EN 13451-2: Swimming pool equipment – Additional specific safety requirements and test methods for ladders, stepladders and handle bends
  • HSG 179, Managing Health & Safety in Swimming Pools (HSG)
  • Pool Water Treatment Advisory Group publication, Swimming Pool Water Treatment and Quality Standards for Pools and Spas (PWTAG)
  • BS 5385-4: Wall and floor tiling. Design and installation of ceramic and mosaic tiling in special conditions. Code of practice
  • Building Regulations Part L Conservation of fuel and power
  • The Tile Association (TTA) Design and Construction Process for Swimming Pools
  • BS EN 1992-3 Eurocode 2. Design of concrete structures. Liquid retaining and containing structures
  • BS EN 1992-1-1 Eurocode 2. Design of concrete structures.  General rules
  • BS 7671 Requirements for Electrical Installation, Institution of Engineering and Technology
  • HSE Assessing the slip resistance of flooring March 2007.

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