huangyhg

hot tub design weight
i have a client who wants to have a hot tub on their deck and am unsure about what design weight to use. i have been told that a 5x5 spa with water and people would be about 5000lb giving it a 200psf load. does this seem right to you? not enough? too much?
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5' x 5' x 3' deep gives 75 cubic feet of water which weighs nearly 5,000 lbs. now add the weight of the hot tub, pump, piping, and at least 4 people but probably a whole lot more during a party and you are approaching more like 7,000 lbs. you should probably assume a pretty hefty safety factor to handle impact loading as well. this will give you more like 300 psf. this is why most hot tubs are mounted on the ground, not on decks.
wow..... no doubt... thanks for the reply, much appreciated!
a second question with this. am i correct in assuming that the weight of the hot tub would be a live load since it's not permanently attached? would it be better to just count it as a dl and include it in seismic calcs for the deck?
yes, i would definately treat it as a live load.
ask the client if they know what models they are using, then you can get the weight of the unit and the water volume to calculate the total load.
make sure that the client is not planning on putting a brick surround or something heavy like that.
last of all, you should put the designed weight and area on the drawings to cover yourself in case they upsize it without telling you (it does happen).
i would think the people and the water would weigh the same. if it were full of water and some people jumped in, the water would overflow.
200 psf is about 3' of water plus some addl dl. i'd say you must be in the ballpark.
how much additional dl would you add? perhaps out of 300psf using 200 as ll and 100 as dl(or vice versa?) to account for some of the water still being in the tub during and event in the same manner as having to consider some of the snow load during a seismic event? i'm also considering not attaching the deck to the house because of the weight but i haven't done that before so i'm not sure what sort of seperation that i might need.
the manufacturer of the hot tub should be able to provide loading information, similar to a cut sheet for mechanical units. that would hopefully answer most of your questions (and any unexpected ones, like a surprisingly heavy motor or the like).
an 8x8 only holds 450 gallons of water, full - 3400 pounds of water. forget the people - they will just displace any excess water. the tub is about 2000 pounds with electric equipment.
still say 3500 pounds including the people, plus 2000 gives 5500# over 64 sq. ft. = 90 psf.
the loading from the smaller tub will not be much different in psf. use 100 psf minimum live load and you will be ok.
mike mccann
mmc engineering
i'm more conservative than many folks, but i would ask how deep the hot tub is from the deck to the lip. then i would use that depth full of water as a design load. if in a seismically active area, i would consider it as a dead load during seismic activity checks. otherwise, i would treat it as a live load. the comment about the displacement of water is very close to my own thoughts.
most hot tubs i recall are around three to four feet tall. so i guess the load would be 190 - 250 psf.
good luck.
just as an example:
enjoy the sweet, sweet sounds of the aquatic melodies? surround sound system in this spacious lounge hot tub model. the elation hot tub is a stellar performer with features that are sure to please even the most discriminating spa enthusiasts.
seats 6 adults
500 gallons / 1893 liters
7'7" x 7'7" x 38" (231cm x 231cm x 96cm)
930 lbs / 6135 lbs filled (424 kg / 2690 kg filled)

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