How to Determine if a Deck Can Support a Hot Tub (& fixes)

I’ve owned 4 hot tubs, but until our current one, they’ve always been on a stone or concrete pad. Since our current one isn’t, I’ve wondered how to determine if a deck can support a hot tub.

Here’s what I’ve discovered:

Yes, you can put a hot tub on a deck. Decks built ground level up to 2 feet off the ground can support up to 100 lbs per square foot; sufficient for most hot tubs. But decks 2 feet or higher will need added support. The added support posts should be no more than 30″ apart & ideally placed in poured concrete.

But there’s a lot more to know about hot tubs and decks. After all, hot tubs, full of water, and people can easily weigh over 5,000 lbs.

So in this article, we’re exploring how to safely put a hot tub on an existing deck.

But we’ll also get into calculating how much weight your deck can support, where to add additional supports to an existing deck. And we’ll even get into what you need to consider if you’re building a deck for a hot tub.

Let’s get going!

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How much does a hot tub weigh?

Before we answer this, let’s look at the different kinds of hot tubs, since each will be different. Let’s also assume we’re NOT talking about in-ground hot tubs.

We have:

  • Small 2-3 person hot tubs
  • Medium 4-5 person hot tubs
  • Large 6-8 person hot tubs
  • Inflatable hot tubs

But the average hot tub weight, empty, is about 500 lbs. Of course, it’s always a good idea to check with your manufacturer about your specific model.

Here’s a handy chart showing an estimate of each of those and how much they weigh (roughly) empty, full, and at capacity with occupants:

Type of Hot Tub Empty  Water Only People & Water 
Small 2-3 person hot tubs 600 lbs 2,575 lbs 3,000 lbs
Medium 4-5 person hot tubs 750 lbs 3,700 lbs 4,420 lbs
Large 6-8 person hot tubs 800 lbs 4,300 lbs 5,500 lbs
Inflatable hot tubs (2-3 people) n/a 2,200 lbs 2,700 lbs
Inflatable hot tubs (4-6 people) n/a 2,700 lbs 3,700 lbs

Can a deck support a hot tub?

As you can see from the above chart, a hot tub full of water and people weighs a lot!

Given how relatively small most hot tubs are, that’s a lot of weight concentrated into a fairly small area on your deck.

So just know that a normal deck raised 2 or more feet off the ground, which might have support posts every 6 feet, won’t be enough to hold the weight of a hot tub.

The good news is that if your deck is high enough off the ground to get under, it’s fairly easy to add support beams and posts to take the weight of your hot tub.

The other good news is that if your deck is just above ground level, you aren’t likely to need additional support.

When in doubt, I would have a general contractor inspect your deck and tell you if it will require additional support.

That being said, if you have a deck that’s just over the ground, it can take about 100 lbs per square foot.

That IS enough to hold most small to medium-sized hot tubs with water and people. But fear not, we’re getting into the exact calculations below.

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How much weight can my deck support?

The higher your deck is off the ground, however, the less weight per square foot it can take.

Let’s break it down, using the large 6-8 person hot tub in my chart above as an example.

  • Weight of the spa (empty) = 800 lbs
  • # of gallons of water (525) x 8.34 lbs (how much a gallon weighs) = 4,378.50
  • Add those 2 numbers = 5,178.50
  • # people (8) x 175 (average weight of user) = 1,400 lbs
  • Add that number to the previous total = 6,578.50
  • Divide that by the number of square feet (64) = 102.79

So as you can see, the largest hot tub is just a hair over 100 lbs per square foot, and that’s if 8 people are in it. For many of us, we won’t have 8 people in our tubs at one time, and we might also have a smaller hot tub.

Need an easy way to calculate square footage? Check out this handy calculator from Calculator Soup.

So if that’s you, and, as I said above, if your deck is ground level or under 2′ off the ground, you should be just fine with no additional support.

Of course, that’s assuming your deck was well-built in the first place AND is still in great shape.

How can I modify my deck to hold a hot tub?

Wondering how to reinforce a deck for a hot tub?

For decks that are high off the ground and/or need additional support, here is a diagram showing you how my deck and hot tub are arranged with the additional support posts that were added under the hot tub area.

Bear in mind, this is what was done at my house (by the previous owners). You should consult a general contractor and check with your city planning office for guidance and permit info.

The added support posts are 30″ apart from one another. Posts ideally would be placed in poured concrete and run at least 1 foot below the frost line.

Of course, if you are modifying an existing deck, take great care to ensure that all footings, joists, and decking are perfectly sound and that no evidence of rot is present.

Can a Trex deck hold a hot tub?

Yes, is the short answer.

Trex is simply a brand name for what’s called composite decking. That’s a fancy way of basically saying fake wood or plastic decking.

Now, I’m not knocking it, but since most of us don’t speak contractor-ease, I wanted to be clear about what Trex is as most of us have seen it.

Composite decking is roughly 20% more expensive than traditional pressure-treated lumber, so it doesn’t fit into every budget.

Now Trex isn’t stronger than traditional wood, so to calculate whether or not you need additional support under your deck to hold the weight of a hot tub, follow my calculations above.

The advantage of Trex comes from the fact that it, like all brands of composite decking, won’t splinter, crack, or rot. Further, it also is highly resistant to mold, mildew, and moisture in general.

While a traditional wood deck might last up to 15 years, Trex and most brands of composite wood will likely last 25 years or more and most come with a 25-year warranty.

Can I put an inflatable hot tub on my deck?

Yes, is the short answer.

Because inflatable hot tubs weigh almost nothing when empty, they are quite a bit lighter than a permanent hot tub.

Using the example in my chart towards the top, we see that even a large inflatable hot tub will likely be about 2,000 lbs lighter when full of water and people than the equivalent regular hot tub.

If we apply the formula I mentioned above for a large inflatable hot tub, we have:

  • Weight of the spa (empty) = virtually nothing
  • # of gallons of water (290) x 8.34 lbs (how much a gallon weighs) = 2,418.60
  • Add those 2 numbers = 2,418.60
  • # people (6) x 175 = 1,050
  • Add that number to the previous total = 3,468.60
  • Divide that by the number of square feet (38.37) = 90.40

So, again, for decks that are basically ground level, most likely you’ll be just fine with no added support for a large inflatable hot tub.

For a deck that is 2 or more feet above the ground, even though it’s not nearly as heavy as a full-sized, non-inflatable, I would still recommend adding the extra support; who knows? You might eventually want to add a full-sized hot tub later on!

Did I cover everything you wanted to know about whether your deck can support a hot tub?

In this article, we took a look at hot tubs sitting on decks.

We explored not only whether that’s a good idea or not, but also how to figure out how much a hot tub weighs (when full). But we also looked at how to figure out how much weight your deck can take.

Ultimately, we answered how to determine if a deck can support a hot tub.

Is your deck on (or going to be) on a deck?

While your deck may only last 15 years, many wonder just how many years a hot tub will last. In a recent article, I break down exactly what the expected lifespan is of in-ground, above-ground, and even inflatable hot tubs.

I even let you know some key tips on maximizing that lifespan too, including the one thing sure to shorten your lifespan by years.

Just click the link to read it now on my site.

 

Jeff Campbell

Jeff Campbell is a husband, father, martial artist, budget-master, Disney-addict, musician, hot tub lover, and recovering foodie having spent over 2 decades as a leader for Whole Foods Market.

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