Can My Deck Support A Four Person Hot Tub?
Existing Footing Layout
I have attached pictures and dimensions (I'm not 100% sure of the footing because the deck was built before I bought my house.).
If it is not going to support it, is there any way I could add supports? I live in Ohio if it helps (snows Dec - March normally).
Can My Deck Support A Hot Tub?
This is by far the most common question people ask. And no answer can be a perfect response to each situation. That is why there are at least six or more of these kinds of responses that I have written.
So I am going to cover off a few things which are specific to your deck as you have described it as well as point to you to some of the other related and certainly helpful articles on the site to let you dig a bit further.
Observations Of Your Existing Deck
Looks like you have four beams evenly spaced supporting your deck and assuming you were to place your tub in the center of the deck we can come up with a couple rules of thumb and some rough weight estimates.
The one thing you have to estimate fairly accurately is your local soil bearing capacity. Everything depends on this number. I have not seen any soil that supports less than 1500 psf but I am sure there are lots of examples.
If your soil supports less than 1500 psf I would bet you are looking at a marsh or very wet location in which case you should seriously consider another location to build on.
So to get you up to speed on some of the things I will be discussing please read this seminal article on determining the load capacity of a deck. It explains tributary areas and soil loads. Understanding deck and soil load capacity
How Much Weight Are We Talking About?
A common tub size for 6 people with 420 gallons will weight about 3507 lbs for the water, 1000 lbs for the tub and 2000 lbs for the six big people. The total is over 6500 lbs. That is on the heavy side.
So if we divide that by the area of the tub (8x8=64 ft2) (6500/64=101.56 psf) we get approximately 101 psf.
A residential deck should be designed to hold 50 psf (40 psf live load and 10 psf dead load). Let's add the dead load of 10 psf to our number and we get 111 psf in the area under the tub.
If we have just four footings of 1 sqft under the tube creating four rought equal tributary areas of 16 sqft each footing will have to carry 16x111 lbs or 1776 lbs over our 1 sqft footing and we have 1776 psf
What is our soil bearing capacity? Is it more or less than 1776 psf?
To play it really safe I would add two more footings under the tub to create six equal tributary zones of about 10.5 sqft. That results in each footing imposing only 1166 psf on the soil? So the more footings you have the less load per square foot is imposed on the soil.
Your tub is only for four people and it is inflatable so the numbers will be less.
How Do You Add More Footing Under The Deck?
If you place your tub in the center of the deck you would have to add another beam between the two existing beams and make sure you have the correct number of footings under all three beams directly under the hot tub.
This is hard hard work. It means removing a lot of decking to expose the joists and then it means hand digging a number of new holes to the right depth and diameter. You can dig less holes if you increase the area of each footing.
But anyway you look at it you have a lot of hard work ahead of you. Once the cement has cured you can install the support posts and beam so they fit snuggly under the framing. Expanding a deck with a hot tubMore Tips On Preparing For A Hot TubReinforcing A Deck