or years, pool builders have offered the same two choices to homeowners: a free-form pool that can’t accommodate an automatic cover or a basic rectangular vessel that can.
An automatic cover needs rigid, straight boundaries for it to sweep back and forth. A free-form pool, on the other hand, conforms to no specific shape. This means automatic covers have been out of reach to customers who prefer free-form pools.
A new method helps solves this age-old problem. While a couple of builders have been using it more than a decade, it’s new to most. Some manufacturers call it the “extreme cantilever” because it shows the least evidence that there’s a cover. And with the right engineering, it can even accommodate a raised bond beam with sheet waterfalls.
Here, builders address this pricey and complex solution — and seven ways to make it work.
1 Special engineering.
Unlike a regular pool, with its straightforward shell construction, the extreme cantilever incorporates three parts. It starts with the free-form walls built as usual. then an under-deck is set back from the curved contours to form a rectangle on which the cover mounts. Over this lower level, another deck will hang, following the lines of the pool wall. When the pool is finished, the cover sweeps back and forth underneath the deck. (Illustration of an extreme cantilever)
It looks similar to a pool-in-pool application, with a free-form vessel surrounded by a rectangular expanse of concrete that steps up to a higher level of deck. This whole structure is shot with gunite or shotcrete, with the bond beam sitting at the rectangle’s perimeter. The cover track is mounted on the step-up. Unlike the pool-in-pool, the lower area is capped with an overhanging deck made of reinforced concrete. Builders leave a void between the lower shelf and the cantilevered deck for the cover to move back and forth. The only proof you have of this construction is a cavernous area at or slightly above the waterline, which is most visible from inside the pool.
Due to the special engineering, extra materials and slow work required by this method, builders report charging as much as 20 or 30 percent extra for gunite and shotcrete. They tend to receive 40 percent more on fiberglass installations. (More details on fiberglass installations.)
2 Placing the gap.
The cover gap can be placed at the waterline or just above it. Many builders place it where the tile line would normally go, so that approximately half of it rests underwater. That way, the pool looks close to normal: It has about the same amount of freeboard as any other project, and water conceals part of the gap. The water helps keep the “shelf” underneath the cantilevered deck clean.
Some homeowners with children prefer to place the gap above the waterline for safety’s sake. “One homeowner said, ‘I don’t want my child to climb up and get his head stuck underwater,’” says Jason Lott, president of Paradise Pools & Construction in Lindon, Utah.
On the plus side, this version allows for a tile line. But it has additional freeboard, and the void is completely within view. With the cover placed higher, you don’t have to worry about it touching and kicking up water as it opens and closes. This method takes more concrete because you have to build the bottom shelf up higher. It’s a must for fiberglass or vinyl-liner pools, where the shell and bond beam are separate.
3 Sizing the gap.
You’ll need a gap that’s large enough for the cover to move without rubbing on concrete. It should allow for an arm to repair or replace the tracks, but it shouldn’t be large enough for children to climb inside. To accommodate the cover, Lott’s supplier advised him to make the gap at least 2 inches larger than the cover’s leading edge.
Builders report using as little as a 5-inch space. Steve Chandler, president of Custom Pools in Boise, Idaho, thinks 6 inches is a minimum to allow access. Dan Tietsort, owner of Gem Gunite Pools, also in Boise, prefers 8 inches for more access.
Chandler likes to turn the lead bar upside down, so it can move more easily in a tighter space. “But when you do that you have to be careful you don’t get it so low that it scoops up the water when you close it,” he says.
4 How far to cantilever the deck.
The farther the deck overhangs, the more support it will need — and the tougher it will be to reach the tracks for maintenance or replacement. Lott lets the design dictate the maximum overhang. Access shouldn’t be a problem, he says, because the deck will curve in at spots, allowing easier entry.
But some builders place a limit on how far their decks will cantilever. Chandler, for example, limits it to 30 inches or less. “We figure that’s about as far as your tech can reach underneath,” he says.
Jay Tucker, owner of Swim World Pools in Gallatin, Tenn., makes it a goal to minimize his cantilever. “It goes anywhere from as little as a foot to 2 feet,” he says.
5 Supporting the deck.
After the client signs on the dotted line, pick up the phone and call a structural engineer. These professionals will figure out how thick to make the deck and what kind of additional support it needs.
Expect the decks to go thicker than normal with a beefed-up steel schedule. Lott’s have been as thick as 51/2 inches.
Tietsort’s engineer has specified No. 5 rebar placed as close as 4 inches on center. When the steel schedule gets that tight, he pumps the concrete rather than shooting it. This prevents voids, ensuring that the steel is completely encapsulated.
The engineer probably will design some type of counterbalance for the overhanging deck. Usually, this means pouring the deck back far enough to counter the weight of the cantilever. “It’s kind of like a diving board effect,” Tietsort says. “If you were to get out on the edge of the pool deck and jump up and down, you’d have the weight of the [counterbalancing deck] keeping the whole thing from going down.”
In these cases, the engineer should tell you how far back to take the deck. Expect it to be substantial. Lott’s engineer designs it twice as large as the cantilevered area. Because of that, these pools generally don’t work in tight areas. In addition, raised bond beams or waterfalls will require additional support, Chandler says.
Your engineer also may tell you to tie the deck to the bond beam. If so, Lott says, leave rebar dowels sticking out of the bond beam at the interval dictated by your engineer. The gunite crew might balk at trimming a bond beam with the bars sticking out, but make sure you insist that they do it. Epoxy doweling after the job is completed would not work — all the rebar in the beam would make it nearly impossible to drill deep enough for a proper dowel.
Do not tie the deck to your pool unless it has been specified by a professional structural engineer.
6 Providing access.
You may be satisfied that the cover gap will allow enough access to the track and pulleys, but you can still provide easier access in the right places.
Tietsort strategically draws the contours of his pools to curve in where access is most needed. “On the shallow end where the pulleys would be or there might be problems down the road, that’s where the pool noses in,” he says. “The areas that are seldom accessed are widest.”
Tucker provides additional access to the pulleys on the far end of the pool, opposite the cover box. He creates openings in the deck near each corner of the pool, and caps them with the pour lids used for skimmer covers. “You can lift those up to access the other end of the track to be able to pull any ropes out for future service,” he says.
Skimmer access also can be a problem if you place the gap above the water because it gives you extra height above the waterline. If this happens to Lott, he attaches the basket to the skimmer lid with a string. When the homeowners or their children pull the lid, the basket can come out with it.
7 Forming the deck.
Shaping the deck to mirror the pool takes time and attention to detail. Use flexible bender board for the deck’s front form. On concrete pools, you can use the walls as a built-in template, nailing the front board to it. For fiberglass or vinyl liner, you may need to create a template for the bender board out of plywood.
The true challenge lies with forming the cantilevered deck. Crews need to set the forms in such a way that they can be easily removed from the narrow cover gap.
On Tietsort’s first pool, his workers stacked sheets of polystyrene to form the gap. Then they poured the concrete on top of it. “We thought it was a great idea; it doesn’t stick to anything,” he says. “But once we got it poured, it’s hard to get the [polystyrene] out of there. It took us a couple days to dig all that out.”
What works best, these builders say, is a series of 2-by-4’s turned on their sides to function as framing or supports, and then plywood for pouring the deck itself. “After we pour the concrete, we knock the 2-by-4’s out and the plywood drops down,” Tietsort says.
In addition, Chandler has his workers screw rather than nail the forms together. “They can be unscrewed and pulled out from underneath,” he says. “When we used to nail everything together, we’d have to almost chop [the forms] out.”
Lott has another trick up his sleeve. His crews prop up the 2-by-4’s with shims. These wedge-shaped pieces measure 3/4 inches thick at their widest points and sit underneath the vertical supports closest to the cover track. “It’s all wedged in there enough that nothing’s going to move,” he says.
To remove the forms, workers pull out the shims. “Now your forms will start to drop 1/2 inch, so they’re not directly up underneath the ledge,” Lott says. “Then you can start pulling them out.”
