Deck pro explains how to build a structure to support a hot tub off the ground
For more than 30 years, Bill Renter owned a landscape design/build firm, The Deck & Patio Company, which he recently sold. The company built decks, patios, pergolas and ponds, and did all the landscaping in between. Many those projects involved incorporating a pool or hot tub. Eventually, Renter went on to sell hot tubs and now owns Long Island Hot Tub.
“Since a large part of our business was building decks, many times a deck would be more than 3 feet off the ground,” Renter says. “In order to integrate a hot tub into it, we would have to [create] a structure that would be strong enough to hold it.”
Renter developed what he calls a spa cradle, using 6-by-6 pressure-treated railroad ties or timbers from Home Depot. “They are so strong and it’s an easy material to work with, and readily available,” Renter says. He got the idea after a training class building timber-framed homes. “One of the things that stuck out when they were talking about timber-framed houses was the strength of the post and beam construction. The post can support up to 100,000 pounds of weight before it fails, and we have four of them underneath our hot tub. That’s 400,000 pounds of available weight — we knew they were not going to fail. It was building the same structure as we were for decks, just using different components.”
Using a post-hole digger, they dig four footings 3 feet deep (below the frost line) and 12 inches in diameter. “We want all four footings and all four posts underneath the hot tub so there’s not any cantilevers,” Renter says. “All the weight is directly over the footings and the force, or compression, is directly underneath the hot tub.”
Next, metal brackets called Simpson Strong Ties are attached to the posts. “These metal brackets are used for house construction and made specifically for a 6-by-6 post,” Renter says. The posts sit on top of the brackets and then are cut down to level.
Two horizontal beams are placed on top of each post. One horizontal beam spans across two footings, and then four go the opposite way to create a platform/structure for the hot tub to sit on. “We want to support the outer edges of the hot tub and the center where the footwell is,” Renter says. “Those four joists are long enough to stretch to the outside of the hot tub. The footings don’t have to be right at the corner, but we want to have the two outside joists pretty much at the edge of the hot tub. Then two at the center — we want them spaced apart but supporting the footwell because that’s a point load.”
The beams are spiked together with 12-inch galvanized spikes or large screws. Renter says the spikes ensure they don’t shift, because once the hot tub is filled, the compression force keeps things in place. After doing these for many years, Renter has learned how to get the best result for his clients and any service needs. “We’re the trusted adviser,” he says. “We’re the people running the show, so we when get commissioned to be the trusted adviser from the client, we suggest the best way to do it.”
To start, they always try to have the access panel on a side where the deck won’t be built up to it. “A lot of times we position our spa cradles and hot tubs in a corner of a deck, so it’s actually exposed on two sides,” Renter says. That makes it easy to service, he says. And if the hot tub needs repairs that require it to be moved, after the electricity is disconnected it can be slid off the deck.
The deck wraps around the hot tub on three sides. The access panel, usually where the topside control is located, is also facing out. If the hot tub has to be completely enclosed by the deck, they create a 2-foot access space so they can get in, remove the panel and work on the hot tub.
The first time Renter ever built a structure like this, he was 18 and living with his parents. He built and installed a redwood hot tub flush to a deck in their backyard. “Now that I’m older and wiser, I like my hot tubs 16 or 18 inches above the surrounding surface,” he says. “It makes it much easier to get into. You can step over the side and land on the seat or sit on the edge and swing your legs over.”
Having the hot tub above the deck surface also allows for most cover lifts to be installed. “The [cover lift] brackets mount high, so there’s room for the bar to open and it doesn’t hit the deck or anything,” Renter says. “For a standard cover lifter it usually works fine.”
If the hot tub is flush with the deck, he uses a CoverShelf. “It just sits flat at about the same height of the hot tub, so it doesn’t block any views and it puts the cover in a place where it’s out of the way,” Renter says.