On the High Rise: The Special Challenges of Podium Swimming Pools
Monday, October 7, 2019
Over the past couple decades, advances in construction technologies along with the ability of designers to push the envelope have opened doors to unique opportunities in the aquatics industry. One such advancement has been the recent popularity of podium pools, also known as high-rise pools. These vessels are built on the second floor of a building or higher.
Beyond the obvious difference that a podium pool is not constructed in soil, several unique features set these pools apart from in-ground pools. The differences are quite evident even in the early design phases.
The planning and coordination required for a project becomes magnified when it involves construction on a challenging site. Podium pools perched on upper floors of mid-rise and high-rise buildings provide some of the most challenging design scenarios. Their complexity demands careful design intent beginning at their earliest stages, with each element requiring careful consideration.
Pool Geometry: Have You Provided Ample Space?
If you’ve ever seen the excavation of an in-ground pool, you’ve noticed that minor adjustments can be made to the size, shape, and depths of the pool up until the tractors leave the site. Since the earth is a relatively malleable medium, shapes and depths can be changed with several scoops from a backhoe’s bucket.
With podium pools, changes to the pool are not as simple. Before installing the pool shell itself, crews install a structural vault – a concrete box that serves as something of a foundation for the pool. Once that vault has been constructed, the pool must fit in the space provided. The building structure provides a rigid, immovable, permanent vault size.
The size, depths, and type of pool must be well-planned, usually before the building structure is designed. There are no do-overs that don’t have hefty price tags. For example, if a designer wants a 4-foot water depth, then building a 4-1/2-foot vault will not suffice. The box needs to account for any freeboard distance between the water surface and the pool deck, the thickness of the pool shell, and the space required to accommodate pool plumbing beneath the shell. Where it was once thought a 4-1/2-foot vault depth would be sufficient, the space may actually need to be 6 feet deep or greater.
Fixtures and fittings installed within the pool walls may increase the plan dimensions as well. For example, a pool skimmer or underwater light niche could require up to 24 inches of horizontal distance between the inside vault wall and the finished pool surface.
Once the pool vault has been constructed, modifications would prove very costly and cumbersome. In addition, the demolition crew could likely damage or destroy a portion of the waterproofing system that’s so vital to the building’s success. To provide a vault that will support the pool, aquatics designers and architects must carefully communicate the design to the structural engineer during early stages in the design.
The Dreaded Pool Leak: Preparing for the Inevitable
It’s unfortunate, but pools leak! Where a minor leak in an in-ground pool may go relatively unnoticed for months or even years, in an on-structure pool, it can become a major issue in a matter of days. So the success of a podium pool depends greatly on the extent to which leaks can be mitigated.
This begins by properly addressing the building structure. In most cases, a void space will exist between the back of the pool wall and the inside face of the vault in which it’s built. Leakage that occurs when the shell cracks or from rain will migrate to this area. It is critical that this space be drained, and that proper drain piping be installed throughout the building structure to remove this water.
Additionally, consult a waterproofing expert for guidance on the best methods and materials for preventing water migration into the building. Once the pool is constructed, there is no economical way to retroactively address pool leaks. Therefore, this step is critical and should not be underestimated.
Pool Equipment: Considerations for Locations and Types
Most podium pools utilize either flooded suction or self-priming pumps that require a constant source of water for their operation. Therefore, it’s best to install the mechanical equipment beneath the pool as this will help ensure the pumps have a constant source of water. This eliminates the need for more costly and inefficient pumping systems.
Designers may have to choose the filtration method based on space allowances. Typically, high-rate sand or cartridge filters are used. But often, space allowances dictate the size and slope of sewer lines that will be routed through the building. Sand filters may be ruled out if the backwash flush exceeds the sewer line’s capacity. Cartridge filters, on the other hand, can be cleaned with a significantly reduced volume of water, making them the only option for some projects.
The Pool’s Piping System: Design Considerations
Bends and fittings in piping are known as the primary source for plumbing leaks in a pool. To proactively address or eliminate leaks, the design should place strong emphasis on minimizing the number of fittings used. When possible, plumbing should run in a relatively straight path to the equipment room, with as few bends as possible. In addition, the mechanical room should be as close to the pool as possible. This decreases the length of pipe runs and necessary fittings.
Where pool plumbing is exposed to the weather, insulation must be wrapped around it. This not only prevents pipe rupture due to freezing, but also minimize the condensation that can drip into habitable spaces. However, the insulation can add several inches to the pipe’s outer diameter, affecting installation in narrow pipe chases.
In many pools, a pump moves the water through the plumbing. However, some designs work best with gravity systems. As the name implies, these rely partially on gravity to move water from one location to another. However, these systems take up more space than their pressurized counterparts so the must be strategically planned during the design phase.
Wind: The Forgotten Factor
One design consideration that is often overlooked or forgotten is the impact that high winds can have on the upper floors of a tall building. These forces typically become stronger the higher you get above ground level. It stands to reason that the water in a pool placed 30 stories above the ground will be “rockin’” when the winds are strong. And these forces sometimes are magnified by the wind tunnels created by the positions and geometries of nearby structures. This can result in a significant loss of water, as it is blown out of the pool. Vanishing-edge and knife-edge pools become especially susceptible to water loss as they have minimal freeboard – that space between the water level and the deck.
Rain curtains, deck jets and similar features also will see significant water loss in a high-wind scenario. The design team may want to consider a system that reduces or terminates flow to these features during a high-wind event.
Final thoughts: The proactive approach
While podium pools present a variety of design considerations, challenges and even pitfalls, there is a tried-and-true method for guaranteeing their success: Be proactive!
The first step: Hire designers with plenty of experience in this field. This is not the project you want your consultants cutting their teeth on. Where guesswork and assumptions may suffice on less significant projects, they can be at best very costly, or even catastrophic for podium pools. Consultants well-versed in podium-pool design will help ease insecurities and provide insight that can save time and money.
Communicate the intended design to the consultants at the beginning stages of the project so the correct sizes of the structural vaults can be provided.
Failure to communicate early will lead to unnecessary problems along the way. But careful discussions during the design phase will produce a timeless pool that sits high atop your city’s most elegant building.