Hot Tub Support

[XR250]

I am working on verifying some deck reinforcement that a contractor did for a new hot-tub. Whenever I design these supports i assume that the weight is distributed evenly over the hot-tub footprint. His position is the majority of the weight is concentrated around the footprint of the base of the footwell - which makes sense. Due to some framing irregularities, his reinforcement only works if this is the case. I have tried reaching out to the tub manufacturer however their offices are closed due to the stay at home order. Can anyone confirm his statement?

Thanks

 

[Celt83]

I wouldn't think the fiberglass shell can resist the water weight so likely some structure under each of the seats plus you have the pump out on the perimeter. It is likely the footwell being the deepest portion contains the majority of the water weight but I'd guess there is still a decent amount of load in the other areas.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[SteelPE]

IDK, I was always taught to place the load on the floor uniformly under hot tubs (inline with your initial design approach). I would have a hard time believing that the load in concentrated in certain areas.

 

[BAretired]

One hot tub advertisement I saw recommended a minimum of 100 psf design load, but hot tubs vary in cross section, so I would want to see details of the particular tub being installed in your case. You can't verify what you can't see.

BA

 

[phamENG]

I can see two ways of thinking about it:

1) Fiberglass shell supported on a wood frame distributes the load in a slightly less than equal way (because nothing is infinitely rigid, of course). Add to that the pumps and other equipment that is probably concentrated in one spot and you have a good case for equally distributing the load.

2) Look at it from a progressive collapse viewpoint. If you spread it out evenly, what fails first and how does it fail? Do joists start deflecting too much? If so, it may not be a problem. If there's a stiffer load path from the frame to the reinforced portion, that's where the load is going to go. This is probably harder to prove, and you'll probably have to get the contractor to take the skirt off of the hot tub to see how the frame is built and how stiff it is.

 

[kipfoot]

You might get some insight by looking at hot tub installation instructions. Those that I saw stress the importance of a continuous level base because this supports the bottom of the tub. I think this confirms your initial approach.

 

[XR250]

I suppose the actual load distribution is somewhere between the two. Maybe I'll swag the load distribution and see if i can get comfortable with what he has already framed.

Thanks for the help!

 

[ldeem]

I recently bought a hot tub and did a lot of research on different designs. From what I learned lower end hot tubs tend to rely on supports under the foot well and seats since the shell will not support water weight. At the higher end the tub is more rigid and will support water weight, in this case the load goes to the frame, so more of a permiter load.

For reference I bought a higher end tub and checked my deck using 100 psf on the hot tub foot print.

 

[JLNJ]

100 psf doesn’t seem like enough. That’s only 19” of water.

Maybe the water is more shallow over the seats than I envision.