Hot Tub Deck Support Question

by Jason Foster

I know this has been asked before, but of course it will always very per deck/hot tub being considered. I'm a mechanical engineer so I have technical knowledge about things, but this is not something I frequent in my line of work.

Description of hot tub:

Intex Purespa
Can hold 210 gal, which with water having density 8.34 pounds/gal give me a total weight of 1751.4 lbs.
Inner diameter: 58" (4.833ft) (area = .25*pi*4.833^2 = 18.35ft^2)
Purspa weight (no water): ~110 lbs
Seating capacity 4 people: 500 lbs likeliest
If I add up all the weights I get 2361.4. If I take that and divide it by the pool area of 18.35ft^2 I get pretty much 130 lb/ft^2.

Description of deck:

Shape (plan view): imagine a rectangle with a trapezoid on top
Dimensions (plan view): Width is 23'-6". This width is the same width as the back portion of the house it connects to. I assume that it connects to the house the full span. Height, from bottom of rectangle to top of trapezoid is around 20'; height of the rectangle accounts for at least 16'.


Posts appear to be either 3x3 or 4x4. Posts and a main wooden joist are located along the horizontal line where the rectangle and the trapezoid meet. There are five supports evenly spaced that hit the main joist. I'm not exactly sure about the spacing between the beams/joists that run from the house to the main joist. Also, there may be additional support along the sides of the rectangles, but sides have stairs, but I can't tell right now since it's night and I wanna start doing something in the morning.

Floor Planks:

The don't run directly vertical nor horizontal, but at 45 degree angles.

My concern is of course that I don't want the deck to fail anywhere, but I wonder if the deck around this portable tub would be subject to caving in at 130 lbs per square foot?

I would imagine if I had 18 people stand hugging each other that it wouldn't have a problem, but I'd like to get an opinion by someone who has more deck knowledge. There may be additional supports, but I can't see that right now since it's night.

Also, would you think just in general that the deck would have any issues supporting this additional weight? At five posts, that amounts to an additional 500 lbs per post. Lastly, I'm imaging, the best placement for this would likely be in the center of the deck.

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