Hot-Tub on an Exterior Deck
Hot-Tub on an Exterior Deck
(OP)
Does anybody have any experience in designing a deck attached to an existing house, which needs to support a hot-tub? I have asked the arch. for footprint and weight when the hot-tub is full. Are there any specific requirements for supporting that kind of load? (I'm thinking I may need to use double wood joists depending on the load)






RE: Hot-Tub on an Exterior Deck
RE: Hot-Tub on an Exterior Deck
TTFN
RE: Hot-Tub on an Exterior Deck
If you need to use wood, it is possible. You need to check shear stress and make sure that the hangers are adequate.
RE: Hot-Tub on an Exterior Deck
Always the tub manufacture has provided the weight of the tub full of water and with the weight of the number of people the tub will accomodate. They usually use 200# per person. The deck indeed has to be stout. Remember along with the tub weight there is usually several people around the tub.
Get the weight from the manufacture or decline the job.
RE: Hot-Tub on an Exterior Deck
The SouthernPine site has span tables for 150 lbs/ft joists:
http://newstore.southernpine.com/images/ref202.pdf
RE: Hot-Tub on an Exterior Deck
RE: Hot-Tub on an Exterior Deck
The critical element to check is probably the joist support to the house. Install some Simpson hangers if you don't have them already. Either way, if it's a typical residential deck, it will not support the weight of a hot tub without some retrofit.
RE: Hot-Tub on an Exterior Deck
Incidentally, the standard tubs around here are 7'x7'x37" high, with 345 gallons of water and 5-6 persons. Self weight of tub is around 500-600 lbs and total weight is a bit over 4000 pounds - way too much for a typcial wood deck. (Especially when you throw in the reductions for wet service, pressure treated, etc)
RE: Hot-Tub on an Exterior Deck
It depends on the builder, i.e. how well it is framed. I have one on a wood deck, and it's performing fine. I'll be replacing the wood in a few years (since it was built in 1996), but it shows no signs of distress. (It's about 6 feet off the ground - on dolomitic limestone. I can get close to the supports without much trouble.) The deck is in better shape than the spa, incidentally -
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"
RE: Hot-Tub on an Exterior Deck
If you do support it on the deck...using galvanized joist hangers (or stainless steel) is critical since the tub will have some chlorine in the water and will corrode the steel for the hangers.
RE: Hot-Tub on an Exterior Deck
RE: Hot-Tub on an Exterior Deck
The decks and balconies that fail do so during an overload event, such as a large crowd at a house party. In your case one can just imagine, after a few drinks, a group deciding to see how many people they can fit into the hot tub!
The Royal Australian Institute of Architects have initiated a "Balcony Week" to pulicise the potential problems with these structures and to encourage owners to complete annual checks (http://www.medialaunch.com.au/257/).
Be conservative in you design/check!
RE: Hot-Tub on an Exterior Deck
The problem, generally, has not been the member sizes (floor joists etc) but rather the connections between the legder and the main house and lateral stabilirty of the columns.
Generally, contractors will only nail the ledeger board to the main house rim. This is INADEQAUTE. The nails corrode, "loosen up", begin to pull-out etc. The ledger board must be bolted to the rim board with, preferably hot-dipped galvanized, thru-bolts or lag bolts (or lag screws if you prefer that nomenclature). Many local building departments realizing the problems have required contractor have decks "engineered" depending on the size. Many are also requiring the ledger be bolted if not requiring the deck "engineered".
Several years ago (maybe 5-6 years), a magazine (I think it was This Old House) published an artilcle on this topic and had several details in the article. I no longer have the article, but I used those details and incorporated them into my practice with some modifications.
RE: Hot-Tub on an Exterior Deck
4 post,one at each corner of the deck. If the deck is very high it will need cross bracing, the bracing should be thru bolted with 1/4 bolts. The bracing style needs to be X pattern on all four sides most often. The girders need to be strong in the tub area. I would use a 2 2x12 to make a beam for the girders and use 2x10 joist at 12 inches on center all attached with metal brackets. Because decks shack. And hot tubes are heavey. As far as the post size i can not size them i do not know the heigth of the deck or were the tub will set on the deck.