Do you know how to determine if a deck can support a hot tub? Adding a hot tub to your backyard space can be a difference maker. After all, who doesn’t love being able to come home from a hard day’s work to enjoy a relaxing soak?
The key is to make sure that you place your hot tub in the correct spot. Some will recommend placing your hot tub on some sort of concrete base. That is a great idea but it also is not absolutely necessary.
You can actually keep your hot tub stationed on your deck as well. The key is to make sure that the deck is graded to support the hot tub.
But how do you know if your deck is meant to hold up to the weight? Thankfully, you can determine if your deck will be able to support it relatively easily.
Decks that are built at ground level that go up to two feet off of the ground are able to support roughly 100 pounds per square foot.
At that support weight, it should be sufficient for supporting most hot tubs. It is when you have a deck that is two feet or higher from the ground that you need additional support.
Still, there is a lot more to know about the entire process. Besides, hot tubs that are full of water can weigh up to 5000 pounds or more.
So, How Much Does a Hot Tub Weigh? This is not necessarily the simplest thing in the world to answer. After all, hot tubs come in different sizes and have different capabilities for holding water.
There are more than a few types to focus on before figuring out what the hot tub weighs. There are small hot tubs that can fit two to three people. A medium hot tub would fit four to five people.
Large would fit six to eight people and an inflatable hot tub would hold one to two people at the most. On average, though, a hot tub will weigh about 500 pounds when empty.
When in doubt, check with the manufacturer for the specific weight of your model. Here is a good rule of thumb for each type.
For an inflatable, you can expect it to weigh about 2700 pounds with water in it and about 3700 pounds with people added in. A small hot tub will weigh about 2600 pounds with water in it and 3000 pounds with people added in.
Medium hot tubs will weigh about 3700 pounds with water and 4400 pounds with people. Larger hot tubs would be around 4300 pounds with water and 5500 pounds with people added in.
With those weight estimates factored in, you can safely estimate what your deck would need to be able to support before installing your hot tub.
How To Determine If A Deck Can Support A Hot Tub
As you can see, hot tubs can be extremely heavy even on their own, let alone when water and people get added into the mix. Not only that, but hot tubs comprise a relatively small surface area.
That means a lot of weight being concentrated on a very small area on the deck. For a raised deck that is two or more feet off of the ground, you may typically find support posts every six feet or so.
That is not enough to hold the average hot tub, so you will need to add support. The good news is that if your deck is high enough, you can get underneath to add support posts with little issue.
That added support should be enough to hold your hot tub. Of course, if your deck is just above ground level, you likely will not need to add in supports at all.
If you have doubts about whether or not your deck can support a hot tub, bring in a general contractor. They can inspect the deck to tell you whether or not additional support is required.
Remember: most decks that are just above ground are able to support roughly 100 pounds per square foot. For most small to medium-sized hot tubs, that is more than enough to hold the weight of a full hot tub.
How Much Weight Can My Deck Support?
While those are good general rules to operate on, it does not necessarily tell you whether or not your deck can hold up to that kind of weight.
And the higher up your deck goes, the less weight per square foot that it can support. Let’s look at the large hot tub — the kind that can support six to eight people at once.
To get the weight per square foot that you need to support, take the weight of the empty spa, add in the number of gallons of water and the weight of a gallon (8.34 pounds) and add them together.
Then, take the number of people and multiply by the average weight (175), adding it to the previous number. Then take that total and divide it by 64 (the number of square feet) to get the weight per square foot.
That number comes in just above what most above-ground decks can handle. There are also plenty of calculators available online where you can calculate the pounds per square footage as well.
But there are other factors involved as well, such as how well built the deck was and the condition that it is in now.
How to Modify a Deck to Support a Hot Tub
Unless you are going with a small to medium-sized tub, you may have to add in support. Decks that are more than a few feet off of the ground may be spaced every six feet.
Supports will likely need to be added in every two to three feet or so. In some cases, it can be up to 30” away from the next post. Ideally, you would place your posts in poured concrete and keep them about a foot or so below the frost line.
Make sure that you consult a general contractor first and even check with the city planning office for any necessary permits or guidance.
When modifying an existing deck, make sure that all the joists, footings, and decking are sound and that there is no evidence of rot anywhere.
This is not the kind of project that any DIYer should take on. It requires skill and knowledge to ensure that things are done properly.
If you feel as though it is above your skill set, don’t be afraid to bring in a contractor to handle the job for you. It will result in a much better overall quality and provide you the peace of mind that you need.
What About Trex Decks?
Trex, which is just another name for composite decking, is another type of decking. Composite decking is typically made of a “fake” wood or some type of plastic.
And while it may sound as if it is some kind of cheap knockoff, there are definitely positives and negatives to Trex decking. For starters, composite decking is about 20% more costly than your standard pressure-treated lumber.
So you’re paying more right out of the gates and it isn’t budget-friendly. Composite decking is also quite a bit less sturdy than traditional wood. So if you use composite decking, you will have to factor in any necessary additional support.
The advantage to composite is simple: it is much more durable than traditional pressure-treated wood. Composite decking does not crack, splinter, or rot. It is also extremely resistant to mildew, mold, and moisture.
Think about it this way: traditional wood decking may last about 15 years or so. Composite decking, meanwhile, will last 25 years and even longer, with some having a 25-year warranty attached to them.
Can an Inflatable Hot Tub Be Used Instead?
The short answer is that, yes, you can. Keep in mind, however, that an inflatable hot tub may not be quite as light as you think it is. Water and people weigh what they weigh and there is no eliminating those weight costs.
The good news, though, is that they weigh quite a bit less when empty. Still, you need to do the math to find out if your deck is rated for handling the weight of the water and people in the hot tub. The math is relatively the same.
Take the weight of the spa (which should be far less than your standard tub) and add it to the number of gallons times 8.34 pounds. Then multiply the number of people by 175 and add the two totals together.
Divide that by the square footage (most inflatable tubs are around 40 square feet) and you will have your pounds per square feet.
Whatever the case may be, it is important to not only know how much weight per square foot your deck can handle but what your hot tub will come in at.
The better prepared that you are, the better your deck will be at standing up to the weight. When you have the proper support, then you can use your hot tub comfortably and without worry.
Hello, my name is David Zal and I’m a plumber with more than 20 years of experience based in Englewood (Florida). I like to teach normal people how to make easy fixes in their homes. I believe that a lot can be achieved just with DYI and that’s why I started this blog.