Weight of a Hot Tub

by Bob
(Victoria, BC)

Your website is very informative, although unfortunately my handyman skills are zero. I am looking for your thoughts.

We had our deck built on our new home to hold a hot tub. I am concerned with some of the corners cut in other areas of our home build so wanted to see what you thought.

Our Deck is 10x20, the hot tub end has been constructed with Doubled up 2x8 Joists 16" on centre, with a single 4 ply 2x10 Beam running between the posts.

I did have an engineer do the math for me but I now see a depression in the Duradek coating on one corner of the tub.

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Jul 25, 2010
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Load for a hot tub deck
by: Editor - Rich Bergman

Given I don't have much details to go on I will try to cover a few general points about hot tubs on decks as this is a very commone question. Let's take a tub that is on the larger end of the scale, seats 7 people, 96x96 to probably weigh 900 lbs empty. Holds 500 gallons - at 8.35 lbs per gallon that is 4175 lbs. Add in 7 people at 200 lbs and that is 1400 lbs. The grand total is 6475 lbs.

Add in a safety factor of 1.5 x and that is getting close to 10,000 lbs over an area of 64 square feet or 156.25 psf.

A typical deck is designed for a load of 50 psf. So two things come into play. Have you framed the deck strong enough to hold the load mentioned above and I wonder if you have as you only mentioned one 4 ply 2x10 beam. Where is the other load point? Is it the ledger? If so you really really want to be sure that ledger can easily handle that percentage of the load.

The next very important issue is the bearing capacity of the soil. What is it? If it is soft clay you can expect a low bearing capacity somewhere around 1500 psf. Then you need to determine the tributary load areas on the deck and how much weight from each tributary load area is imposed on each footing. That weight will be transferred to a footing and distributed to the soil over the area of the footing. So you need to now how much weight each footing is carrying per square foot and it much be equal or less than the bearing capcity of the soil.

Without details I can't offer you any more than these general guidelines which your engineer will be more qualified to discuss than I am.

Here are a couple of other articles of interest for you to read:

Design Tips
Software to Help with Calculations

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