Hot Tub on Exterior Deck at Height & Self Supported 3

[m_struct]

A client would like to extend his exterior deck to support a 2000kg hot tub (4.4 kips). The new deck steps down from the existing and approximately 4m x 5m in plan, 2.5 m (9 ft) above ground and on sloping site. Is there any guidance for loading, corrosion, and safety for hot tubs on exterior decks?

Loading - The client says the hot tub is 2000kg (tub + water + 6 people). If 6 people are in the tub, how many more would be standing around the tub? What do you recommend loading wise? Dynamic factor for live load (say 2x LL)? Thinking of drunk people and jumping around - high consequence for failure.

Bracing & Layout – Deck is self-supported and about 1.5m below the ground floor of the house. Looking at post and brace on each side of rectangular deck.

Corrosion - Chlorine is present but it is open-air, well ventilated area (open-air). My first thought was with (4) steel posts and beams, with timber decking and joist running over the steel beams. For corrosion purposes, would be recommended to go with full timber? Timber option = 9 posts (3 x 3 grid) with one post at each corner of the hot tube.

Safety – Client wants tub on outside face of the deck. The handrail is about the same height was the edge of the tub, so would that mean the handrail should be double height at that point? Another option would be to recess the hot tub into the deck. This seems much safer and would require a subframe to support the tub. Any suggestions?

 

[JStructsteel]

I would not design that deck for less than 100psf. I have read and seen too many decks fail due to over-crowding. Residential perhaps a bit less severe.

 

[EdStainless]

If you are using treated lumber then use the recommended fasteners. Some treatments are corrosive to SS and you must use HDG (double weight) for corrosion control.

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P.E. Metallurgy, consulting work welcomed

 

[STrctPono]

Ed,

You are certainly the expert, but don't you meant to say that some treatments are corrosive to HDG and must use SS? I was always under the impression that after the treatment industry voluntarily removed Chromated Copper Arsenate treatment from residential applications the alternative solution was to use Copper Azole or Copper Naphthenates with higher copper concentrations than the previous CCA treatments. The higher copper content meant that zinc coated fasteners would degrade faster and they therefore recommended SS fasteners. Isn't stainless steel more noble than copper? I also was under the impression that the tannic acids in cedar and redwood would stain HDG fasteners and cause streaking?

 

[m_struct]

For earthquake loading, it is recommended to use full dead load of hot tub (unit + full of water) or can it be assumed that XX percentage of the water splashes out in a seismic event? Thus the seismic dead load = unit + XX percent full of water.

 

[EdStainless]

For some you are correct, but some treatments contain salts that are aggressive to SS. It isn't one size fits all.
And yes the staining is a fact, in those woods I would use SS.
In treated lumber make sure that you look up the recommended fastener metallurgy.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[m_struct]

Thank you for all the information here. A summary of the advise that I am hearing:
[ul]- Hot tube should be ground bearing if possible
- If elevated, advised to use a steel subframe to support hit tub and normal deck around
- Decks should be tied back to the house structure, if possible[/ul]

 

[cvg]

just fyi, most hot tubs use Bromine, not Chlorine. I believe bromine is more corrosive than chlorine.

 

[m_struct]

If the hot tub in ground bearing on concrete slab, does it bear directly on the slab or does it need slightly elevated off the slab, supported on skids or equivalent? For the slab - 5" reinforced concrete slab on compacted hard fill?

 

[phamENG]

Hot tubs on decks typically fall outside of prescriptive codes. If your building department doesn't have a guide that you can use, you'll need to hire a local structural engineer to design it for you.