Category Archives: Design

How deep does my pool need to be for diving?

Like most questions, the answer depends on several factors and decisions. The first factor is deciding on what level of diving competition or training you wish to host.  There are several governing bodies such as USA Diving, NFHS (High School), NCAA (Colleges and Universities), and FINA.  USA Diving governs club level diving competition while FINA is the international governing body for World Championship and the Olympics.  Each have their own diving requirements and swimming pool design guidelines.  Quite often, we are asked to design an aquatic facility that will host several of these types of diving competition and training.  In these cases, we design to the most stringent standard which is typically FINA.

Heritage Park - HendersonAfter you have landed on the level of competition or training you wish to host then you need to decide on the second factor: springboards or platforms or both.  Springboard training and competition takes place at 1-meter and 3-meter heights.  At elite venues, a minimum of two 1-meter and two 3-meter springboards are installed. Platform diving competition takes place at 10 meters, though 1-, 3-, 5-, and 7.5-meter heights are also typically provided for training and warmups.  Occasionally, a ½-meter platform is constructed for divers to practice takeoffs.  A facility without a 10-meter platform can host a platform diving event on a 5-meter platform if the teams competing agrees on this height.

The majority of the venues we design at High Schools and municipal/club level type pools opt for 1-meter springboards. Often two 1-meter springboards are installed to provide more throughput during practices and meets.  The minimum swimming pool depth requirement for 1-meter springboards is 11’-6” but we recommend adding 6” to this depth for a total depth of 12’ to allow for any construction errors while building the pool. If a 3-meter springboard is also installed the minimum swimming pool depth requirement is 12‘-6” but again we recommend adding 6” to take it to 13’ deep.  As mentioned above, when platforms are installed, diving competition typically takes place on either a 5-meter platform or a 10-meter platform.  The depth requirements for these are 13’ and 17’ respectively after adding the 6” recommended tolerance.

Now there are many pools across the country that have shallower pools that would like to provide diving to its patrons for purely recreational purposes. We see many pools that have 10’ to 11’ deep diving wells.  In this existing condition situation, we would need to review the pool floor contour to see if a diving board can or should be installed.  In many cases a lower, more rigid diving board can be installed.  These are often ½ meter or ¾ meter diving boards that are very rigid.  Think back yard pool diving board but more suitable for commercial applications.  Utilizing this type of diving board may allow a pool depth around 10’ deep.

Diving from starting blocks and from the side of the pool also depends on many factors. In general, diving from the side of the pool should be limited to water deeper than 5’.  Diving from starting blocks, like diving boards, depends on the height of the starting block above the water.  At 30” above water level, which is competition height, we recommend a minimum water depth of 6’ and there are even some states that require 2-meters or 6’-7”.  Lower starting block heights may allow for a lesser water depth.  In conclusion, in order to determine the appropriate pool depth for your facility, you will need to study all governing bodies and local codes and understand the ramifications of your design decisions.

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How can geotechnical issues affect my pool structure?

Certainly one of the least conspicuous but most critically important design considerations for an on grade or in-ground commercial swimming pool structure are the geotechnical conditions (soil conditions). Variations in geotechnical conditions can drastically influence the design approach for the pool structure, pool shell construction methods, and in some cases the pool maintenance protocol as well.  Soil properties can dictate the difference between a simple slab-on-grade design and a more elaborate structural solution requiring deep foundations, over-excavation, soil conditioning, subsurface drainage, piping encasement, or some combination of the like.  This blog post will provide a brief introduction into the basic geotechnical considerations influencing pool shell design.

An early step in the design process for any earth supported structural system – be it a building foundation, swimming pool, or bridge design – is to study the geotechnical conditions of the project site. This must be done by a qualified geotechnical engineer who will provide data on the soil properties and recommendations to be used in structural design of the foundation system.  This study is done by analyzing soil samples taken from borings drilled on the project site.  For swimming pool design, it is typically recommended that one boring be taken for each 5,000 SF of pool area, and if multiple pools are included in the project, the borings be located accordingly with at least one taken for each pool.  Required boring depth is determined by the geotechnical engineer based on soil conditions, but in any case should not be less than 5 feet below the greatest excavation depth of the swimming pool.

Data collected from boring samples will be used to determine subgrade soil properties, including but not limited to soil gradation, density, bearing capacity, shrink and swell potential, plasticity, lateral earth pressures, and groundwater conditions. This information is then utilized to determine the most appropriate method of pool shell structural design.  One of the most critical considerations influencing the structural design approach is the swell potential of the soil.  Soil that exhibits high swell potential is known as “expansive soil” and can pose a iStock_000004621785Mediumgreat threat to the performance of an in-ground pool structure if not adequately addressed.  Expansive soils are generally made up of clayey materials which have the ability to absorb water.  These soil types swell or shrink dependent upon the moisture content of the soil.  For certain highly expansive soil types, a volume change of up to 30% may be possible.  As you might imagine, even a minimal volume change of soil supporting an in-ground structure can be catastrophic for a swimming pool shell.  Soil movement can cause cracking of the pool shell, uneven heaving or settlement, and damage to below grade piping systems.

Some common design solutions in dealing with expansive soils are over-excavation of the site to replace expansive material with more suitable soil, and/or structurally supporting the pool shell with deep foundations. When over-excavation is necessary, the geotechnical engineer will recommend the depth to which high plasticity or expansive soils must be removed from the site to limit swell potential.  The soil material that is used to replace the expansive material is known as “select fill”.  The select fill must exhibit the necessary soil properties to limit swell potential and to support whatever structural design approach will be utilized for the pool shells.  It is also very important that the fill material be properly placed and compacted to achieve the density necessary to support the foundation system.

When the structural solution requires deep foundations, such as drilled piers or friction piles, the pool structure is often constructed over a void space designed to allow for soil swell to take place without influencing the pool slab. The deep foundations serve the purpose of supporting the pool shell by distributing the load vertically or by bearing on subgrade material of greater capacity, such as bedrock.  When a void space is utilized, the expansive soil layer is then free to exhibit volume change without exerting pressure on the structure above.  Of course, with this structural solution, the design of the below grade pool piping system must be carefully considered such that soil movement does not affect buried piping beneath the shell.  Structural encasement of PVC piping is a common solution in this design scenario.

Another perhaps slightly less common approach to dealing with swell potential of expansive soils is to moisture condition the soils in order to minimize the possibility of volume change occurring during or following construction. The goal with this method is to saturate the expansive soils prior to construction and maintain the moisture content throughout not only the project, but theoretically the life of the facility as well.  This is only appropriate for certain soil types and generally only those that do not exhibit extreme shrink/swell potential.  Moisture conditioning can take on several forms and may involve injecting water into the native soils; excavating, conditioning, and compacting native soils in a series of lifts; or a combination of these approaches to achieve optimum moisture content.  Once the conditioning has taken place and moisture content of the soil established, it is critical that this be maintained.  Maintenance of moisture content may involve limitations on duration that excavations remain open, capping conditioned soil with select fill or paving to retain moisture, and even irrigation of landscaped areas.

While expansive soils are one of the more challenging soil properties and often one of the first to be considered when determining a design approach, there are many other geotechnical conditions 125509297_e7b05d82bdthat influence the pool shell. The pool wall design – whether it be a cast-in-place concrete wall, pneumatically applied concrete wall, or a stainless steel panel wall and buttress system – must take into account not only the pressure of water acting on the interior face of the pool walls when the pool is full, but also the pressure of the soil or backfill materials acting on the exterior side of the pool walls as well.  This force that the soil exerts in the horizontal direction is known as lateral earth pressure.  The measured or calculated lateral earth pressure conditions based on soil properties will dictate the pool wall structural design and the excavation and backfill requirements behind the pool walls.  This criteria, along with the type of soil, may influence preferred construction methods for the pool shell.  For example, shotcrete or pneumatically applied concrete construction methods for pool walls are most efficient when a vertical cut excavation can be supported and the concrete materials shot against earth.  When very sandy or soft soil is present, supporting a vertical cut to the full depth of the pool excavation may not be feasible.  When this is true the pool excavation must be “laid back” at an angle to prevent the excavation from caving in and pool wall construction will involve formwork for placement of concrete, or a stainless steel panel and buttress system, or a combination of the two depending on the depth of the pool.  The anticipated construction methods based on geotechnical conditions will have an impact on the cost of the pool construction, and also sequencing of the construction among trades, especially for indoor pools where adjacent building foundations are involved.

Another very important geotechnical consideration is the presence of groundwater. We have already discussed in this article the effects of moisture content on certain types of soil, but regardless of expansive soil, subsurface water must be considered in the design of a pool structure as well.  The design must consider naturally occurring groundwater relative to the water table in the area, and also the possibility of surface water infiltration on the site.  If groundwater is present at excavation depth, dewatering methods will be necessary to facilitate construction.  Once the pool is in place, groundwater levels that are above the lowest elevation of an in-ground pool structure will exhibit buoyant forces on the pool shell.  If the pool structure has not been designed to counteract buoyant forces due to hydrostatic pressure, there is risk that an empty pool shell may literally “float” out of the ground causing significant damage or catastrophic failure of the pool system.  If groundwater levels are naturally high on the site relative to the foundation elevation, a subsurface drainage system to remove groundwater from the soil surrounding the pool shell may be necessary.  The subgrade preparation for the pool slab and in some cases the backfill material for the pool walls must be designed to allow for drainage of subsurface water when build-up of hydrostatic pressure is a possibility.  Groundwater levels can fluctuate significantly in certain areas of the country or on certain project sites.  A pool owner or operator must have an understanding of how the pool structure has been designed to perform and whether or not it is safe to drain the pool for cleaning or maintenance.  A method of observing or monitoring groundwater level relative to the pool slab should be provided, such as a sight well or piezometer.  If a permanent subsurface drainage system is installed, it must be ensured that this system is functioning properly before making a decision to drain the pool, especially if the system involves the use of pumps to remove water.  Hydrostatic relief valves in the pool floor are another fail-safe against the effects of hydrostatic pressure on an empty pool shell.

While this post just barely “scarifies” the surface on the subject of how geotechnical conditions can influence the design and performance of a swimming pool, I hope that it has introduced some of the broad topics that must be considered when planning a new pool or even when evaluating issues with an old pool. As discussed, it is critical that a qualified geotechnical engineer be consulted to determine the soil properties on any project site.  Soil properties can vary quite dramatically in some areas, so just because the existing structure on the adjacent site employed a certain design approach does not mean that same solution will be appropriate for your pool project.  Each site must be evaluated according to the project type, and the design solution developed with project goals in mind.  This process of establishing design criteria for the pool structure will ensure expectations are met with regard to cost of the pool shell construction, long term performance of the pool shell, and maintenance requirements.  Simply put, several small holes in the dirt are required to determine how best to fill a big hole in the dirt with water.

What should we consider when purchasing a new scoreboard?

Need a new scoreboard? Here are some items to consider. Selecting a proper scoreboard for either a new facility or the replacement of an old unit is an important decision. Scoreboards in typically big ticket items and can have a big impact on the design of your new facility. Adding a larger scoreboard can also drastically facelift an old facility. In the state of Texas where high school football is king, we have even heard of a school district designing their new stadium around their scoreboard (which was the largest high school scoreboard in the nation at the time of construction) … Everything is bigger in Texas! Here are some industry terms and items to be considered when selecting your new scoreboard:

  • 100_6370Pitch (or Pixel spacing): Think clarity on your TV. The smaller the number the better. 10 years ago the Pitch on “high resolution” boards was 23 MM. Today, economical boards include a 12 mm pitch. Some higher end boards are going as low as 6 mm. 10-12 mm will look from 12 feet away. With the 6 mm scoreboard, you might as well put your grab your popcorn and cuddle up right in front of it (like my high school girl friend’s dad did when their home TV didn’t have a remote.)
  • Active Area: Active Area is the space on the scoreboard that is actually lite up with LED. This will vary from manufacturer to manufacturer as they all have slightly difference LED dimensions and cabinet sizes. The important part to consider is the relative size and to not get hung up on inches. Cabinet size is slightly larger than the Active Area and is really not really important. When comparing different manufacturers, stick to comparing Active Area.
  • Distance and sight lines: The scoreboard should have an appropriate active area that is capable of displaying the number of lanes in the competition pool. The scoreboard may be attached to the wall at the end of the swimming pool or natatorium opposite the diving pool. It should be mounted in a way that it can be seen from the entire deck and spectator areas.
  • Wall Size: Have your architect and pool designer draw the scoreboard on the wall in a 3D modeling program to get an idea on size. Even large scoreboards can look like postage stamps on big blank walls.
  • What sports are being displayed? Each aquatic sport display information is going to lend itself to a slightly different size board. It is important to take this into consideration and even explore potentially having multiple boards for each of the different sports that are going to be a part of a facility.
  • Differences in Manufacturers. There are multiple scoreboard manufacturers for the major sports, however for swimming, there are a few sport specific manufacturers that specialize in swimming scoreboards and timing systems. It is important to have a fully integrated system that is complete with a full timing system and scoreboard. Using multiple manufacturers opens the door for finger pointing on meet day where there is an error with operation of the video system. Going to one supplier is much simpler and quicker when there is an issue.

Hiring an aquatic design professional can help you determine which scoreboard is right for your needs and can help make sure you get the best pricing on your system. Keep this in mind when selecting your design team.

What are the best chemical treatment options for commercial pools?

One of the biggest questions we get asked on each project is about the chemical treatment options. Most people want to select the “best” products available.  The truth is, depending on the specifics of your project, what is considered “best” varies.  For the most part, all commercial aquatic facilities are required to have a halogen in the water for instant sanitation.  The most common types are Sodium Hypochlorite (liquid chlorine), Calcium Hypochlorite (tablet chlorine), Bromine (non-chlorine sanitizer), or Saline (on-site chlorine generator).  Here are some things to consider about your chemical selection:

Sodium Hypochlorite

    • chlorineSodium Hypochlorite (liquid chlorine) is approximately 12% free available chlorine. Sodium hypochlorite must be stored in a covered tank and a room that is ventilated to the exterior. Liquid bleach is a mild hazard. It is relatively reactive with acidic chemicals and organics.
    • Liquid chlorine has some advantages, the most important being safer handling. In a 12 percent solution, liquid chlorine is stronger than the 5 percent solution typical in household bleach and, as a liquid, it’s also relatively easy to monitor and introduce into pool water. Liquid chlorine is injected into the main pool plumbing and is disseminated into the pool. It’s easy to gauge and control. Liquid chlorine costs approximately $1.35 per gallon. Its pH is 13.0.
    • Liquid chlorine also has its disadvantages. Because of its short shelf life, liquid chlorine quickly loses its potency and effectiveness. At the manufacturing facility, the liquid is mixed to a 14 to 16 percent solution, but typically deteriorates to about a 12 percent solution by the time it reaches the supplier and to a 10 percent solution at poolside. Sodium hypochlorite is susceptible to the heat and sun and can drop to as low as a 5 percent solution in one month. Shelf-life is typically between 30 and 50 days. When the tanks are refilled, most are not cleaned out, and the new chlorine is diluted when added to the old chlorine. As a result, potentially twice as much chlorine will be required to achieve the desired effect. Therefore, storing liquid chlorine can quickly become a poor investment.

Calcium Hypochlorite

    • Calcium hypochlorite tablets are placed in canisters and pool water is bypassed through the erosion feeders, dissolving the tablets and introducing chlorinated water back into the pool. Clogging with the feeders was an issue in the past, but most of those issues have now been resolved through design.
    • Calcium hypochlorite is easier to handle than liquid chlorine. It has a pH of 12, so it doesn’t require as much buffering agent as liquid chlorine. It’s more expensive than liquid chlorine (approximately $1.80 per lb.), but it has a much higher concentration of available chlorine (65%). First-dollar costs are similar, and even thought the tablets are more expensive than liquid, the need for fewer buffering agents and a longer shelf life provide trade-offs that make the operational costs manageable. There is no need for the barrier systems and huge storage tanks required for liquid chlorine.
    • Calcium hypochlorite is a Class 3 oxidizer and is corrosive. It has a 4-hour rating with H-2 occupancy or 3-hour fire rating with an H-3 occupancy. It is flammable and high in hazard. Some codes limit storage from 10 to 200 lbs. in a single location. Typically, this amount can be increased if the room has a 2 to 4 hour fire rating, the space is provided with an appropriate sprinkler system and it is properly ventilated. Additional storage of calcium hypochlorite can be provided in an additional “haz-mat” room if the building has such a room.

Bromine

    • Bromine gained interest in the early ‘90s as a replacement for chlorine. Twice the bromine is required to reach the same oxidation potential of chlorine. Bromine is a much less aggressive oxidizer compared to chlorine. It doesn’t combine with organics, therefore chloramines are not produced which cause the smell in a natatorium. There are claims that bromine is less irritating to swimmers.
    • Problems exist with bromine because it is less active, it cannot react as quickly, compared to chlorine, when there is heavy organic loading and a large number of bathers enter the pool at one time. The result is cloudy water.
    • Bromine by itself is costly. First-dollar costs are acceptable, since the distribution system is similar to that used by tablet chlorine. Second-dollar operation costs, though, are significantly higher. Compared to tablet chlorine, bromine can cost a little less than twice that of tablet chlorine. In addition, since it isn’t as active as chlorine, systems need twice as much to achieve the same sanitation level, making the operating costs of a straight bromine system prohibitive for many applications.

Saline

      • Salt systems generate pure sodium hypochlorite at a near neutral pH and therefore have less effect on pH than most other pool chlorines. The pH must be controlled like usual, and is influenced mostly by the total alkalinity of the water.
      • Hypochlorous acid is produced when an electrical DC current is passed between the positively-charged anode plates and the negatively-charged cathode plates in the chlorinator cell. This solution flows, after mixing into the water leaving the filter, directly into the swimming pool.
      • This continuous introduction of hypochlorous acid ensures the continuous sanitization of the pool water and will provide the necessary chlorine residual required when the equipment is operated properly. When the hypochlorous acid produced in the chlorinator has destroyed the bacteria in the pool, it reverts to salt (sodium chloride). This means that salt is continuously recycled during this process.
      • Since the chlorine is ultimately converted back into salt, it gets recycled and extra salt will only need to be added infrequently (only a small amount will need to be added once or twice a year to replace the salt lost due to splash-out or backwashing).
      • Manufacturers report the following advantages of salt systems (most of which are highly debatable):
        • Saves money
        • Fixed costs versus variable chemical costs
        • Improves the quality of the water and enhances bather comfort
        • Stabilizes pH and easier water balance
        • Enhances indoor air quality
        • Reduced pool maintenance and ease of operation
        • Lease payments are tax deductible as an operating expense
  •  Saline systems are often desirable on LEED projects (where feasible). Using table salt with the saline system to create chlorine means that there is no longer a need to store commercial chlorine at a facility as chlorine will be manufactured in-line as needed. Instead, bags of salt will be stored. Also, by converting to CO2, facilities can eliminate the need to store and use muriatic acid and eliminating the potential for spills. By removing most of the hazardous product from the pump room, facilities eliminate the potential for any accidental spills or cross contaminations of chemicals causing fires and or toxic off-gassing, making the facility more environmentally-friendly.Each of these options have been used successfully in commercial applications. It’s best to consider each of these when starting your project, then evaluate the pros and cons based on your specific needs.

What does the ADA require for pool access?

According to the American Disabilities Act (ADA), every pool must have at least two means of ADA access. There are three main means of ADA access that can be considered for pool design:  a fixed pool lift, ramp entry and stair entry. Counsilman-Hunsaker’s standard approach to meeting ADA guidelines is to design our pools with two means of access.  The first means of access is a fixed pool lift on deck required by the Department of Justice.  With multiple pool lift manufacturers, there are many options available.

Our second option is to use a ramp entry. A ramp entry tends to take up a lot of valuable space in the pool. It requires a one to twelve slope and a five-foot landing zone at either a 24-inch or 30-inch water depth. It will also need to be 38 inches wide from handrail to handrail to allow for a wheelchair to pass through. Depending on the depth of the pool, the ramp could be as long as 47 feet. You can shorten this length by adding a switch back at the 18-inch or 24-inch deep landing zone. By doing this, the total width of the ramp could become 8’-4” or 9’-4” if you add a wing wall to separate the ramp from the rest of the pool. Depending on the venue of the pool being designed, a ramp entry might be a must, especially in therapeutic or rehabilitation centers, where most of the users will be in a wheelchair.handicap lift

On the other hand, an ADA stair entry, which is our third option, takes literally no space at all if the pool is already designed with stairs. To make them ADA-compliant, an additional handrail would be added to the stairs 24 inches off of one of the side handrails. Other than the pool lift, this is the easiest option to comply with the ADA since most pool are designed with a stair entry. Cost-wise, it is a lot less expensive to construct a stair entry than it is to construct a ramp entry.

With the options that we have available to meet the ADA requirements, Counsilman Hunsaker’s typical approach is the option of one lift and an ADA stair entry to meet the requirements. If we are designing a pool for a venue that is for rehabilitation or therapeutic uses, we would design the pool with a pool lift and an ADA ramp entry. By adding in a stair entry with ADA-spaced hand rails, we have covered all three means of access.