Design Considerations for Pools Near Florida’s Coast

By Michael Weinbaum, Martin Aquatic Design & Engineering / michael@martinaquatic.com

Construction of pools near the coast has, for a long time, been more complicated than the construction of pools at inland locations.  For instance, it has been a longstanding requirement in Florida to have pools supported by piles when seaward of the coastal construction line.  However, the latest Code updates bring in two new concerns for the Florida pool engineer.  You may be required to increase the uplift loads on the piles, and place the pool equipment in an elevated location.

Engineers need to know two things before considering these two issues.  You need to know the design flood elevation from FEMA Flood Maps and the intended elevation of the floor of the pool.  You must keep in mind that flood maps are regularly updated on a county-by-county basis and ensure you are reviewing the latest online accordingly.  The flood maps will give a zone for each location, identified with a letter and a number.  The letter is the Flood Zone, usually A or V.  The number is the Base Flood Elevation, in feet, relative to NAVD.  Think of the NAVD as the zero value or the typical sea level around the world.  The flood elevation is always above the NAVD, perhaps by 8 feet, perhaps by much more.  You need to know the pool floor elevation relative to the NAVD as well so that the flood elevation can be compared to the floor elevation of the pool.  At the coast, the flood elevation will typically be higher than the floor elevation of the pool. 

With these two values in hand, you can calculate the flood load.  You need to imagine that the pool is empty when the flood comes and that the floodwaters flow through the groundwater such that the pool will have an upward, floating force that the piles will resist.  Also, compare the flood elevation to the top of the pool wall.  If the flood overtops the pool wall, the uplift forces are eliminated.  Therefore, the maximum uplift force, the worst case, comes when the pool is empty but the floodwaters outside the pool are just below the top of the pool wall.

Once the height of the flood water column is known, the loads on the piles will be based on Chapter 1605 of the Florida Building Code. In a coastal conditions, the flood load becomes an important consideration.  Chapter 1605 directs engineers to a national standard, ASCE 7, to find the flood load.  The latest edition of ASCE 7 says that flood loads in V zones and Coastal A zones have higher load factors, compared to flood loads anywhere else.  But what is a “Coastal A Zone”?  The flood map will tell you if the pool is in a V zone or an A zone, but whether the A zone is coastal might not be readily apparent.  Therefore, you need to look for a line on the map called the Limit of Moderate Wave Action, sometimes labeled LIMWA. A-zones that are seaward of this line are Coastal.  Then multiply the flood load by the flood load factor and compare the result to the uplift capacity of the piles.

The second issue to consider is the height at which the equipment should be installed.  The national standard, ASCE 24, was updated to impose requirements on pool equipment.  The 2020 Florida Building Code adopts ASCE 24, but changes the pool equipment requirements to say that the equipment must be “elevated to the extent practical” (1612.4.2, FBC). Building officials are not in full agreement about what the “extent practical” might be.  Some officials are using a rule of thumb that the equipment must be placed 30 inches above the site grade, regardless of if that is above or below flood elevation.  Why 30 inches? Because more than 30 inches would require an engineered retaining wall and perhaps a guardrail, so that might not be “practical.”  Other building officials simply comment that everything needs to be above the flood elevation and leave it to the contractor to respond that this is impractical.  For example, the pool’s design may include a flooded suction pump, and it may not be practical to elevate the flooded suction pump at all.  It is certainly not practical to elevate a heater to the point that one can’t operate its controls, or a filter to the point that the operator would need a ladder to perform routine cleaning.  As this is a relatively new requirement, it may often be up to the contractor to carefully educate the building official during the permitting process.  To help educate builders and building officials, the Florida Division of Emergency Management website, www.floridadisaster.org, has published a document called “Interim Pool Guidance” that can be found by major search engines.