After building my deck and enjoying it for a while, I began to wonder how I could go about making it even better. Since my deck has plenty of space, I naturally thought about a hot tub. It would be a great way to unwind after a long day, and it meant I could use my deck even when it got cold. But I wondered how can you put a hot tub on a deck?
A hot tub on a deck is entirely possible, and it is possible your deck is already equipped to handle one. A deck designed to hold at least 100 pounds per square foot will support nearly any type of hot tub. However, many decks are designed for only 50 pounds of weight per square foot – this will not support some hot tubs and you’ll have to modify the supports beneath your deck.
If you are planning a new deck build, then you’ll first want to calculate the load-bearing capacity of your planned deck. This will depend on myriad factors such as joist spacing, joist overhang, footing size, soil type, and more. Then determine the overall weight of your desired hot tub at full capacity – humans included.
Already have a deck? No problem, because it is entirely possible to modify your deck supports to account for a new hot tub. Below we’ll go into detail about how to plan for a hot tub on a new deck and modify an existing deck to hold a hot tub.
- Types Of Hot Tubs for Decks
- Do You Need a Permit for a Hot Tub?
- How Much Does a Hot Tub Weigh?
- How Much Weight Can a Deck Hold
- How to Determine if Your Deck Can Support a Hot Tub
- How to Reinforce a Deck for a Hot Tub
- Designing a Deck to Hold a Hot Tub
- Composite and Cedar Decks and Hot Tubs
Types Of Hot Tubs for Decks
There are a wide variety of hot tubs, and even this is an understatement. You may have heard of portable hot tubs, vinyl, and even inflatable hot tubs.
We’ll also only be using the term “hot tub”, and not “jacuzzi” or “spa” because Jacuzzi is an actual brand and a spa often references a more advanced type of in-ground hot tub with more features.
Below we’ll clear up what is what when it comes to hot tubs so you know exactly what you need to buy – or not.
Portable hot tubs include everything from inflatable hot tubs to very hot tubs that can be moved as an individual unit. Many “portable” hot tubs are not actually very portable due to size and weight. However, they have that designation because all of the equipment required to operate the tub is contained within the hot tub unit.
Below is information about the various types of portable hot tubs.
Inflatable hot tubs are just that – they come in a (large) box and need to be inflated. Often they come with proprietary pumps, such as the Coleman inflatable line of hot tubs.
These hot tubs are anywhere from 60 – 100 pounds when deflated, making them a truly “portable” hot tub. Typically these are made from a multi-ply vinyl – a.k.a PVC. Imagine a giant, really, really sturdy inner tube – that’s an inflatable hot tub.
Inflatable hot tubs, of course, don’t come with a pump, filtration, or any other equipment within. There is a standalone unit that comes with inflatable hot tubs that connects to the tub, functioning as the pump, filter – if there is one – and other plumbing required for the inflatable hot tub to function.
Since the weight of these tubs is far less than the other tubs, you can put one on a deck. For instance, a four-person inflatable hot tub holds around 220 gallons of water. That’s around 1700 pounds without people. Add 4 medium-sized people, and you are looking at nearly 2500 pounds.
If you have 2500 pounds of hot tub and person on your deck, and your hot tub’s diameter is close to 7’, then you are looking at roughly 75 pounds per square foot on your deck. Most decks must be built to withstand at least 50 pounds per square foot. So there is a 25 pound per square foot discrepancy.
However, with some modifications to your deck frame and foundation, your deck can safely hold a fully inflated and occupied inflatable hot tub.
An acrylic hot tub has an inner shell made out of acrylic, with an outer shell made of another type of material that covers the insides of the hot tub. One of the most common types of “portable” hot tubs, these are popular because they come in copious amounts of different styles since the outside shell can be customized for a wide variety of looks.
The acrylic shells are often made with either fiberglass layers or ABS layers beneath for added reinforcement. Top of the line models has thin sheets of steel in areas of the tub that need extra-reinforcement.
Acrylic hot tubs can be heavy. It is not unusual for an empty hot tub to weigh close to 1000 pounds. A 7 or 8 person hot tub filled and occupied can reach upwards of 6000 pounds – that is no easy weight for a deck to hold.
Can a deck hold an acrylic hot tub? Absolutely. However, special considerations must be taken when framing and installing footings. The deck structure will need to be reinforced significantly before you plop a larger acrylic behemoth on your deck.
Also known as polyethylene, these types of hot tubs are all one unit of molded plastic. There is a mold filled with plastic powder, then the mold is turned as the exterior of the mold is heated. The powder melts and is evenly distributed throughout the mold.
In many aspects, a molded – or “roto-molded” – hot tub is similar to a giant plastic bin with jets. It is far more lightweight than an acrylic hot tub – anywhere from just under 200 pounds to over 400.
The portability of these tubs, combined with their toughness, makes a good option to place on a deck. Since these hot tubs are a fairly simple design, they are also cheap. While not quite as cheap as inflatable tubs, they can still check in at around $2000. Higher priced models are bigger and offer more features, but still don’t compare to the hefty price tag of an acrylic.
A roto-molded tub runs on a regular household, 15-volt outlet. That means they are not huge drains on your electrical bill. The downside is that it takes a long time to heat them because the pump and heater are designed to work on the said outlet. Also, they lose heat quickly due to their all-plastic body.
Do You Need a Permit for a Hot Tub?
Sometimes. A permit is fast becoming a requirement for many municipalities across North America. Check with your local building services department to find out if it is required where you live.
For instance, you do not need a permit for a hot tub if you live in Houston. In Tampa, you don’t need a permit if the hot tub is not hooked up to plumbing or hard-wired to your electrical system. However, you do need one if you live in Toronto or Los Angeles then you do need a permit for a hot tub.
Remember, you do not need to erect a fence around your hot tub if you have a cover that locks. This will ensure your hot tub passes code.
A deck with a railing over 6 ft. from the ground, with locking gates at all entry points, will also suffice for a hot tub on a deck without a locking cover.
Lastly, some jurisdictions only require permits for hot tubs that have an 8 foot or longer stretch of open water. Smaller hot tubs in those places do not require permits.
How Much Does a Hot Tub Weigh?
Luckily, determining the weight of your hot tub empty, filled, and fully occupied by a group of people is fairly simple. Since we know that water weighs about 8.3 pounds per gallon, we can accurately calculate hot tub loads.
Therefore, we’ll simply be taking the manufacturer’s specs for the dry weight of hot tubs and the average weight of the North American adult – 178 pounds. Combine those two factors with our weight of water per gallon, and we can easily discern if your deck can handle any type of hot tub.
Below we’ll take a look at the weights of several different types of the hot tub. All weights are in pounds (lb.)
|Type||Dry Weight (Empty)||Weight with Water||Total Weight (Water+People*)
*at full capacity
|Inflatable, 2-4 Person||70||1540||2250|
How Much Weight Can a Deck Hold
A deck’s load-bearing capacity can get confusing, so we’ll try to make this as clear as possible.
The construction of a deck is made easier with charts that outline the maximum lengths of your joists, posts, and beams. They also include variations for different joist spacing, lumber type, and footing type.
If you build your deck to code, abiding by all the structural requirements as outlined in your local building code, then you’ve only built your deck to support 50 pounds per square foot. Why? This is the default – and most common – standard for deck building, and it won’t be enough to support most hot tubs.
Since deck load charts only include loads of 50 pounds per square foot, decks will need reinforcement to hold a larger hot tub. Luckily, there are deck load calculators available online that can help you adjust your joist span and sizes to accommodate a heavier load.
Unfortunately, these are only helpful for new deck builds. Plus, you also have to know the maximum weight of your new hot tub.
Remember, a standard deck built to code is only rated for 50 pounds per square foot – that includes a 10 pound/square foot dead load (the weight of the actual structure) and a 40 pound/square foot live load (anything on the deck surface, such as people or a hot tub).
When you put a 4000-pound hot tub on a deck, your live load doubles, at least. Therefore 50 pounds per square foot will not work. Also, keep in mind that the weight of a hot tub is concentrated in one area, so it is likely that you’ll need even more reinforcement in that one area because the weight is not spread out and can skew your support calculations.
How to Determine if Your Deck Can Support a Hot Tub
The best way to explain if an existing deck can hold a hot tub or not is to compare an existing 10 x 10 deck built to code without a hot tub on it. Standard deck beam charts show acceptable spans with various types of lumber and plys, that will support a 50 pound per square foot load.
As I’ve already explained, that calculation will not work for a hot tub. Remember, it doesn’t matter how high off the ground your deck is or not. If the deck is off the ground by even an inch, the same thinking applies – you’ll need to reinforce your deck.
To determine the load-bearing capacity of your deck, you’ll want to know the tributary area of your deck posts. That’s how much weight each post can hold. Let’s say your 10×10 deck is supported by 3 posts plus a beam at one end, and a ledger board on the other with joists running perpendicular to your house.
To find the tributary load of a post, multiply half the length of the joist – including any distance the joist cantilevers over the beam – by half the distance of the beam on both sides of the post. If our beam is at the end of the deck, with no cantilever, then half the distance of the joist is 5’ and half the beam length on either side adds up to 5’, too.
So, if we multiply the two together, the tributary area of the middle post on our 10×10 deck beam is 25 square feet. Now, multiply that by 50 pounds/square foot and you get 1,250 pounds. If you were to place a 7-person hot tub in that tributary area, with a total weight exceeding 4,000 pounds, then you could risk structural failure and injury – or worse.
If you look at this tributary load chart, it will show that if you keep your tributary area low – meaning you include more beams and/or posts – then the maximum length of a post of any size will be quite high – 14 feet. This means that the most effective way to reinforce your deck is to add more posts and beams.
And then there is snow load to consider. However, if you’ve accounted for the total weight of your hot tub and reinforced your deck accordingly, then snow shouldn’t be an issue simply because a deck built to code will take into account snow load based on typical winter conditions for that specific geographic area.
Lastly, remember that the height of your deck isn’t as important as how far apart your posts are spaced and the size of your posts. If you have a deck close to the ground, you could still encounter issues if you don’t have enough posts.
How to Reinforce a Deck for a Hot Tub
Modifying an existing deck will require more posts, and perhaps another beam. But how do you accomplish this without tearing up your deck and starting fresh? There are several ways you can go about altering your deck without starting over – here are a few methods below:
Add A Beam
Adding a beam to fit between two existing beams – or a beam and a ledger board – is possible, and potentially easier than simply adding a post to an existing beam.
To add a beam, you’ll need to remove deck boards. Once removed, you’ll have to operate between your joists. If they are 16” apart or more, this is possible.
If you are installing patio stones with deck blocks on top, then your job is fairly easy. You can also install screw piles, working around the joists.
What you cannot do is dig a footing beneath an existing deck unless your deck is high enough off the ground for you to fit under. If you can, then digging is probably your best option to support a post.
Add a Post
Adding a post beneath an existing beam is tricky, simply because if your deck is within 5’ of the ground, then getting underneath the beam and digging isn’t an option. At best, digging in those circumstances is extraordinarily uncomfortable. Therefore, you need to find another way to support the beam.
One way is to level the earth beneath the existing beam for a patio slab, deck block, and adjustable post holder or post.
This does not give the same amount of added capacity that a new beam would, but adding several to a beam can reduce the tributary load tremendously and increase the deck’s load bearing capacity at the same time.
Designing a Deck to Hold a Hot Tub
Keep in mind that when designing a new deck with a hot tub on top, you’ll only need to add extra reinforcement to the area right below the hot tub. So instead of overbuilding the entire deck to account for the added weight of the hot tub, you build a deck to standard code and reinforce the area beneath the hot tub.
On the other hand, it may be easier to add another beam to your new deck, even if it spans beyond the footprint of the hot tub, just for peace of mind and consistency in design.
Whichever method you choose, you’ll need to consult with the calculators linked above from the AWC, as well as the span tables, to see how far apart your joists need to be, how many posts you’ll need, and how to size your deck beam.
Overall, the best way to hold a hot tub is a concrete pad. A pad with a deck built around the hot tub will let you rest easy at night because this is by far the best way to support a hot tub, particularly a larger one that gets experience loads beyond 5,000 pounds.
Composite and Cedar Decks and Hot Tubs
If you are building a deck with Trex composite lumber, then you’ll have to keep in mind that a standard 12’ Trex deck board is almost double the weight of a standard treated deck board. Be sure to reference a Trex-specific beam span chart when planning a deck and hot tub using Trex lumber.
Cedar framing will have considerably less weight-bearing capacity compared to SYP structural lumber and somewhat less than SPF – reference this load bearing chart. This will have to be considered when adding a hot tub to a deck made completely from cedar lumber.
Sizing a new deck or adapting an existing deck for a hot tub can get complicated and involve lots of math. Above I’ve shown you some tools and resources you can use to help you figure out how to safely install a hot tub on your deck.
If at any time you are unsure about whether your deck can handle a hot tub, then call a certified structural engineer instead. Accidents involving decks and heavy loads are more common than you’d think, so having a professional stamp of approval is always worthwhile.
Thanks again for taking the time to read this post. If you have any questions or concerns then feel free to drop me a line – I’d love to hear about your next deck and hot tub project!