They dazzle perched atop a high-rise hotel or apartment complex. They provide fun and exercise in enclosed spaces both residential and commercial. Or they can hover in multi-level subterranean spaces.
While these installations often are shorthanded as “rooftop pools,” the correct term is podium pools — because they will be supported by structural members on the building such as beams, pillars and vaults. And they can sit at any level, as long as it’s not in the ground.
While these installations have always been prevalent in commercial buildings, they are becoming more common in residential settings — particularly in urban areas — as space continually tightens.
But these installations represent risk exposure at least as dramatic as their aesthetic. Without exaggeration, this construction may represent the highest liability out there. If something goes wrong, the best a contractor can hope is that water drips or concrete chips fall on a car parked in the garage below. But even then, many vehicles parked in these settings bear names such as Porsche or Mercedes, so you don’t even want that.
Then there’s the worst-case scenario. “Imagine the sort of damage you can do to that building if 15,000 gallons were to drain out of that swimming pool, and then the cost to tear it out and rebuild it — which I’ve seen,” says Rob Holmer, a principal engineer working from the Sacramento, Calif. office of national engineering firm Terracon.
Even with minimal collateral damage, that pool will need to be fixed. Such repairs can prove difficult because of access issues.
Podium pools also require intense construction measures. If concrete, the shell will have heavier than normal reinforcement. When weight or space is a concern, jobs may call for stainless steel pools, with their approximately 3/8-inch-thick shells. (And these are becoming more price-competitive than before, landing them on more drawing tables.)
Regardless of the shell type, it will require proper drainage and waterproofing.
Follow these tips to help you graduate to this level of construction.
1. Accept that you will need help
When the most renowned builders in the country installed their first few podium pools, they started by finding somebody to offer guidance.
These pools involve more than following provided specifications. Building engineers will spec the support structure; however, they often rely on the pool contractor as an expert to fill in the knowledge gaps. There likely are hundreds of details that they haven’t considered — and that most backyard pool builders don’t have to deal with.
For instance, contractors see one mistake made by architects and engineers repeatedly — underestimating the necessary dimensions, especially the depth, of the vaults that often contain these pools and spas. These professionals frequently take the pool’s depth, add the expected thickness of the pool shell and leave it at that. For a 4-foot-deep pool, for instance, they may specify a 4½-foot-deep vault. But this doesn’t account for plumbing and other elements that reach outside the pool.
Paolo Benedetti is addressing that issue on a project he’s currently advising. “They already had the vault poured, and I had to explain, ‘This isn’t deep enough. By the time I add plumbing, drain sumps, our steel and all the clearances, you’re going to lose a foot of depth, maybe 18 inches,’” says the president of Aquatic Technology Pool and Spa in Morgan Hill, Calif.
Architects and engineers also may not know about the extra bonding requirements for these pools or where penetrations are needed in the vault.
To step in and provide this level of expertise, first-timers should seek guidance.
2. Expect each project to be different
It may sound cliché, but when it comes to support systems for podium pools, no two are alike.
“There’s no bag of tricks you can use,” says Rick Chafey, co-owner of Red Rock Pools & Spas in Mesa, Ariz.“I have yet to work on two that were the same. … Especially in the residential world, you can get in all kinds of different situations.”
Many engineers support these vessels in a vault, but other podium pools rest on beams or pillars. “In other cases, the pool might … just be freestanding on top of a concrete slab,” says Terry Brannon, president of The Brannon Corporation, an engineering and consulting firm based in Tyler, Texas. “Then pedestals hold up the deck and landscape.”
In vault pools, many engineers add a separation layer between the pool and vault. This helps shield the inner vessel from building movement and prevent cracks in the vault from reflecting through the pool or spa shell.
Terracon usually uses geofoam, a structural-grade polystyrene product, for this purpose.
3. Master waterproofing and drainage
Approach any professional with experience in podium pools, and they will start with waterproofing. These pools require multi-pronged systems that likely incorporate most every type of waterproofing available — admixtures in the shotcrete, a membrane of some type inside the shell, sealants in and around the penetrations, and maybe even a waterproofing agent on the back of the shell, if it’s exposed. In the latter case, though, make sure the product is suitable for the negative face. If it isn’t, Brannon says, then water migrating through the wall can cause a membrane to peel off or otherwise become compromised. And, as with any product, make sure it is appropriate for the application and compatible with the other waterproofing products and pool finishes.
But pools leak and condensation occurs, so designers also must devise a way to channel runoff away from the pool and building. “You want a drain that daylights somewhere, whether it dumps into a floor sink in the equipment room or goes all the way down to the ground floor, with a pipe coming out of a wall and daylighting somewhere,” Benedetti says. This gives a visual sign of a leak.
Vaults must contain drains running water away from the area. If the pool is built without a vault, then some type of containment must be installed underneath the shell.
To help with drainage, Brannon likes to place a ½-inch-thick drainage mesh or mat between the pool and vault. This also provides separation between the pool and vault.
4. Work to higher standards and codes
For the shotcrete or gunite, a 2,500-to-3,000-psi mix likely will not suffice. Experienced builders typically start at about 5,000 psi, then the compressive strength increases from admixtures.
In these applications, Holmer and his team design to a different code from the American Concrete Institute (ACI). In everyday situations, shotcrete shells should be designed to comply with ACI 318. However, Terracon designs podium pools to meet ACI 350, which is meant for concrete tanks such as those used in municipal applications. “Though it’s impossible to design concrete so it won’t crack, you can design [it so] the cracks are so small that they remain watertight,” Holmer says, describing the purpose of ACI 350.
These pools will have more reinforcement than normal. Some of Holmer’s projects are built with No. 5 bars at 5 inches on center each way.
5. Expect exponential planning time
These pools require meticulous planning by the pool contractor and its subs. On the design/engineering side, plumbing schemes will have to be drawn out, with penetrations planned in advance. The method of supporting the pipe to prevent vibration and wear, such as using struts and clamps, must be figured out.
Contractors must know what they’re building around. Air-conditioning ducts, gas lines, computer and electrical conduit become factors. “When we’re working in a … building structure, we have to dodge everybody else,” Brannon says.
For this reason, Chafey adds, pool builders must be able to understand the plans and drawings for other trades.
On the construction end, access and scheduling must be choreographed. All trades may share a construction elevator or crane, so their use will have to be arranged. “There’s a schedule coordinator who will give you a time to use that crane,” Chafey says. “Sometimes you have to pay for it; sometimes you just have to block out the time. And then you have to make sure your stuff is on site when they’re ready.”
Those shooting concrete or applying finishes must decide if their pumps can work from ground level or if equipment must be lifted to the site. When pumping from ground level, they also must devise a way to ensure the hoses don’t cause any damage. “When you’re running hoses down the side of the building, you have to protect the buckles on the hoses with foam so, if the hoses bounce, you don’t have an issue with it smacking into the wall,” says Dave Schilli, president of St. Louis-based Schilli Plastering Co. “A lot of times they’ll tie the hose off at the top [and bottom] of the wall to [reduce] vibrating.”
When they take on especially tricky or large podium-pool jobs, plasterers Dave Cooke and Rob Romano visit the site, devise a plan, then go back to the site another one or two times to make sure they’ve covered all the bases. As the work draws closer, they’ll do at least another mental run-through in the office. “We’re not just going to show up and go, ‘Okay, here we go,’” says Romano, general manager of David Cooke Plaster Co. in South Windsor, Conn., of which Cooke is president. “It’s all planned out well in advance.”
6. account for the elements
Many of these pools straddle indoors and out. A rooftop pool will sit outside, while its structural support and plumbing rests in the ceiling of the floor below. The underpinnings of an indoor pool may hover over a parking garage. This can cause issues with freezing and condensation.
In areas prone to freezing, always insulate pipes exposed to the outdoors, Brannon says. This also applies to main drains that are exposed.
Insulation also may be needed to minimize condensation, which can form around pipes and leak through ceilings.
Stainless steel pools often are insulated with foam for this purpose. It also helps eliminate hollow sounds. “When you’re inside the pool and you stomp around, you don’t want it to sound like you’re inside a barrel,” Brannon says.
Also consider condensation if a pool sits next to steel I-beam structures from the building, Benedetti advises.
