Deck Strength for a Hot Tub

by Dan
(Portland, Oregon)

I have an existing deck that is 16' wide (ledger on house) and is 12' long I have two 6 x 6 posts at each outside corner.

It has double 2 x 12 on each side and then a 2 x 12 joist at 16' oc. The floor is made of 2" mahogany. the builder thinks it will hold a load of 5000 lbs from a hot tub.

I think i need to put some posts underneath for support. Will the deck as it is currently constructed carry a hot tub that will weigh 5000 lbs when full?

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Sep 21, 2012
You are entering Structural Engineer territory
by: Editor-Rich Bergman

A classic question I get all the time. You have to get a structural engineer to look at this. What I can tell you in a general sense is that the dimensions of the joists and frame structure including the deck boards should easily support a hot tub of that weight.

But that does not mean the deck will not fall down!

You have a ledger attached deck. This means that connection is even more critical. There are two load locations that take all the weight of the structure and the hot tub - the ledger and the carrier beam.

If your ledger connection is strong enough and the beam is also sufficient the next question is how much load is imposed on the soil under each support post and is this force less than the bearing capacity of the soil.

I can't possibly answer any of these questions without observing every detail of your deck. So do yourself a big favor and get an opinion from a local structural engineer. Too much is resting on it.

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