The design of an elevated pool or water feature is not inherently complicated, dangerous or even necessarily problematic, but it does include some interesting challenges that can be terribly unforgiving of ignorance or neglect. Some basic issues that should be considered whenever such a design is undertaken include the following.
Pool Shell Design and Construction
- Weight of pool and equipment: The weight of water alone is about 62 pounds per cubic foot. The load of the water, pool shell and structural containment can easily total 350 pounds per square foot or more, depending upon the structure and the actual water depth. A careful structural analysis will be required.
- Double shell pool/water feature construction: There are two generally accepted approaches to the construction of elevated pools and water features. Both entail the construction of a waterproofed structural well within which will be constructed the pool shell or liner. The first approach of which would be cast-in-place concrete (CIP) or shotcrete and the second of which is stainless steel. Although it is theoretically possible to construct the structural well neat to pool dimensions, a high level of coordination would be required of the structural concrete sub-contractor to insure all pool allowances for finishes, piping sleeves, lights and equipment make this approach very difficult to accomplish, most oversize the structural support.
- Stainless steel pools: The use of stainless steel seems an obvious choice for elevated pools and water features because of its durability and, if properly constructed, water tightness. The stainless can either be left unfinished and bare or provided with an applied finish. Maintenance of the polished surface of the stainless can be an issue, and several health departments require that it be finished for reasons ranging from both color to slip resistance.
- Finishes: Tile is an obvious choice, and very popular for this application for both durability and aesthetics. Several stainless manufacturers also offer an adhered sheet vinyl or PVC finish that may have applicability depending upon budget. Stainless is often nominally more expensive than a concrete solution, although regional preferences may make it the only viable choice. Also, some creative design solutions may find translation with stainless difficult to achieve. Further, if stainless is being used above occupied or in otherwise acoustically sensitive applications, it is recommended that an acoustical engineer be consulted; there is an increased potential for the transmission of noise through stainless.
One of the major keys to successful elevated pool and water feature design is effective waterproofing. Two layers of waterproofing should be considered, one at the structural level and the other at the finish level.
The structural or primary waterproofing system should include the entire natatorium or pool/water feature area, including the well within which the pool or water feature shell is to be constructed, the surrounding deck as well as all ancillary areas anticipated to be wet. The waterproofing material should be consistent with the application, coordinated with and if possible compatible with the secondary waterproofing material under the pool finishes.
The Architect is typically responsible for the base waterproofing system. A drain or drains should be provided at the lowest point at the structural or primary level of waterproofing to carry away leakage and relieve hydrostatic pressure, if any. This drain should daylight at some point, or be provided with a sight-glass, in order to monitor leakage.
Pool and water features waterproofing:
- With a stainless solution, this second level of waterproofing is the stainless steel shell itself. No other waterproofing should be required.
- With a concrete solution, a waterproofing system will be specified that will maximize the compatibility between substrate and finishes.
- Leaks, although rare, remain a possibility. Ideally Piping or conduit should be located in a drained containment area, if not possible, the use of drip pans under the pool and piping may be considered.
- Ample overflow and/or deck drainage capacity at least equal to the makeup water flow should be provided. On high rise applications, the potential for sway should be considered and appropriate measures taken to contain any consequent slosh.
In summary, successful elevated pools and/or water feature design depends upon meeting the inherent challenges and demands of structure, appropriate material selection, waterproofing, drainage and acoustical control.