The deleterious situation of the pool structure

Deck drains

Beyond the pool perimeter, the rooftop deck should be an aesthetically pleasing and functional system of valleys with multiple slopes directed toward specific drains. The types include, but are not limited to, spot, strip, or French drains. The drains are strategically placed by design professionals, and like all penetrations within the pool structure, the drainage pipe is encapsulated within a waterproofing and flashing system to maintain watertightness.

Waterproofing

The waterproofing system is one of the most hidden, integral components of the pool system. It rarely gets the attention warranted. The waterproofing system insures the watertightness of the pool’s structure and spaces below. Waterproofing should be straightforward. However, client ambitions tend toward a complex design and require the need for early collaboration. A continuous multilayer waterproofing system is fully adhered to the pool’s structure, and is designed to be completely integrated into the coping and drainage system. The drainage system is sized and constructed with materials that minimize the impediment of water flow and limit blockages. A waterproofing system with properly terminated penetrations reduces the risk of moisture intrusion. Specifications and protocols that address the complete encapsulation of the entire surface area of the pool structure, including the multilayer waterproofing system, can ensure the necessary construction sequencing is carried out with warranties preserved.

Waterproofing tie-ins are missing in this project.

Crack suppression

Due to high chloride content, water that reaches the steel reinforcement in the concrete can be detrimental to the integrity of the structure. A waterproofing system with a high chemical chloride resistance and hairline crack bridging capabilities should be coordinated with the design-construction team to ensure essential details, penetrations/tie-ins, and separations are considered and worked out among trades.

The design and installation of water-stops within the concrete pool shell structure is an important addition of a well thought out waterproofing system. Water-stops serve as an obstruction of the incidental passage of water through concrete joints. They should be placed systematically between the vertical and horizontal structural concrete elements. The water-stops should be able to withstand a chemically aggressive environment.

Additionally, concrete admixtures can be used to improve durability performance and provide waterproofing characteristics to the concrete structure. Admixtures that are resistant to aggressive chemical environments can also contribute to the watertightness with the ability to self-heal by crystallizing and sealing static hairline cracks. Admixtures provide supplemental waterproofing and chemical protection to concrete water holding structures. This is a means of waterproofing the concrete by way of growing a non-soluble crystalline structure within the pores and capillary paths of the concrete. During the early stages of design, the concrete mix design should be coordinated with the admixture manufacturer’s representative to insure proper dosage and strength. To avoid under-dosage, it is recommended to specify the admixture manufacturer’s minimum percentage by weight of cementitious material requirements to meet its high-performance standards. The modified concrete will be treated as typical concrete, meaning there are no differences when applying decorative finishes or additional waterproofing tie-ins. However, the installer of the surface-applied material (to be applied over treated concrete) is responsible for coordinating and taking the necessary measures to ensure compatibility and bond to the treated concrete.

While industry standards recognize reinforced concrete structures will have cracks to some extent, the pool’s concrete structure requires an approach that is more stringent and limits cracking. Adding to the complexity of the engineering design, a rooftop pool is typically above the parking garage or occupied space. This limits the ability to have a uniform placement of vertical structural supports. The spacing and frequency of these supports is ideally engineered to avoid deflections that would contribute to the cracking of the pool’s concrete shell structure and/or the pool finishes above. Spans exceeding safety guidelines put the pool’s structure at risk and could lead to costly repairs and extensive service interruptions.

While engineering codes and guidelines have provisions for complexity of design, non-uniform spans, and/or other challenges, these only address the structure’s immediate integrity and not its longevity. Additional measures implemented during the design and schematic phases could help reduce deflections. For example, early coordination between the plumbing and structural engineer could reduce the amount of penetrations (and those abandoned) and help with reducing overall congestion. The routing of plumbing, service lines, and pool equipment during design, with specific consideration for easing the installation of waterproofing system and maintenance, would lend to a pool shell structure that could further resist deflections and unanticipated stresses.

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