The average hot tub weighs 8000lbs. Add six or seven adults and the weight could exceed 9000lbs. Understandably, the structure you place under your hot tubs needs sturdiness and sound engineering. For this reason, we recommend hiring a professional deck or patio builder. But if you’re a DIY person, we’ve provided some load-bearing calculations below.
Hot Tub Deck Foundational Calculations
When designing a hot tub deck, you need to determine the size of its posts, joists and beams. To do so, calculate its minimum load-bearing capacity:
- Dry weight + water weight + maximum occupant weight = total weight
- Total weight / square footage = support load
Using the formula above, let’s pretend our hot tub weighs 1000lbs. It holds 2000lbs of water and six people, averaging 185lbs each. The total weight of the tub comes to roughly 4110lbs. If its square footage is 40, then the design must accommodate 102.75lbs per square foot of deck.
The wooden frame that you construct does not support the weight of a hot tub alone. Every spa needs a concrete slab underneath to ensure it remains level and does not sag into the ground. Typically, a 3-1/2 to 4in slab is enough.
Note that elevated decks require professional engineers to design and build. This is law in most municipalities. There are too many variables and concerns to undertake such a project alone.
Hot Tub Design Tips
Hot tubs flush to a deck’s surface are beautifully sleek and modern. Unfortunately, for families, such designs pose a safety risk. Like in-ground pools, children can slip and fall into the spa. That said, keeping a lid locked and closed can minimize the risk. Nevertheless, keeping your hot tub 17-14in above the deck lets bathers sit on the rim and enter/exit the water.
Regarding the position of the deck, consider the following:
- Wind direction
- Placement of trees,
- Coverage from the sun and other elements,
- And privacy.