To install a hot tub on a raised deck, ensure the deck has the right level of support for the weight of the hot tub. The higher the deck, the more reinforcement is needed. But a ground-level deck may not need any added support.
In this step-by-step guide, I will show you what you must do to strengthen your decking.
But we’ll look at how to protect it against the elements, where to position it for the best results, and how to get the hot tub onto the deck, especially if you don’t have a lot of help or if it’s a really tall deck.
Let’s get started.
Table of Contents:
- Step-by-Step Guide to Strengthening Your Deck
- Can a wooden deck support a hot tub?
- Do I need to reinforce my deck for a hot tub?
- How heavy is a 6-person hot tub?
- Where do you put a hot tub on a deck?
- Will joist hangers support a hot tub?
- Does composite decking hold up better under a hot tub?
- Do you have to remove the deck railings before installing a hot tub?
- Does the age of my deck matter when holding a hot tub?
- How do you prep an existing deck for a hot tub installation?
Step-by-Step Guide to Strengthening Your Deck
Key factors in determining the strength of your deck:
- Span of the joists
- Spacing of the joists
- The size, especially the depth of the joist
- The type and grade of lumber
If you are starting from scratch, size the joists to suit the weight of the hot tub. But as you already have a deck, only the first two factors can be changed – you can reduce the span or reduce the spacing. My advice – do both.
Remove the decking boards in the area where the hot tub is to go.
You will have to remove an area slightly bigger than the tub to expose the main support beams. Even if you can get underneath, you will find it easier to work from above than below.
Inspect the ground beneath the deck. Is it concrete or just dirt? How firm is it? Will you have to dig out to form pads for the additional supports?
Measure the size of the joists and the spacing.
We work center to center, so measure from the outside edge to the inside edge, or the space between plus the thickness. Common spacings used in deck construction are 18” and 24”.
Also, measure the span, that is the distance between the supports for the joists.
A header joist is usually attached to the ends of the joists to form a rigid frame and cap off the joist ends. Look at how these are connected. Are they nailed? If so, are the nails tight for the job? Rusted nails or nails that appear too short should be replaced.
Select your lumber wisely. Normally, joists for decking are grade #1, which allows for some defects but not enough to cause any structural issues.
From Step 2, you will have an idea of the size and length you need. Lumber comes in standard lengths of 8’, 10’, 12’, 14’, and 16’, but you can have it cut to length at most lumberyards.
You need to work out for yourself what works best for you but remember, offcuts can be used for support posts.
Although it isn’t important for the new joists to be the exact same size as the existing ones, they should at least be the same depth. Use this depth to mark the underside of the hanger on the header joists.
All new joists must be treated with preservatives, with the cut ends being further treated using a water-resistant seal.
Mark out the midpoint between the existing joists and fix the new hangers in this position. Nail the hanger into the header beam using 3” galvanized nails. Alternatively, if you don’t have a nail gun, use decking screws – one per 2-inch of joist depth on each side.
Slot the new joist into the hanger. It should be a snug fit without any significant lateral movement, and the top should be flush with the existing joist.
Screw or nail through the holes in the hanger into the joist at a slight angle to stop them from pulling out.
— JACK FOUR MAFIA (@StokersPoker) November 19, 2022
Now for the support posts. It is no use strengthening the deck without strengthening the supporting frame, so you need to introduce posts to break the span of the headers.
If the ground is firm enough, you can sit the posts directly onto it, but the chances are you will have to spread the load a little.
For this, you will need a sheet of marine-grade plywood, ½” thick cut to a size of 12”x12”. Nail this to the underside of the post. If the ground is likely to get wet, this should be wrapped in polyethylene.
You may be able to use offcuts from the new joists, but if not, you will need to cut 4”x2” posts to suit the measurement from the top of the header to the ground or baseplate.
The aim is to reduce the span of the header joists to a third of the existing span, so you will need 2 posts to each header, four in total.
Fix the new support post to the header beam using framing anchors on each side. Make sure the top of the post is flush or slightly below the top of the header joist.
On sloping ground, you will need to dig out to provide a level seating for the base plate.
With all the additional joists and posts in place and firmly fixed, carry out one last check on the fixings before replacing the decking. You can use deck joist flashing tape to give greater protection against water penetration.
If you had to cut any of the boards, make sure the ends are properly treated before fixing them back in place. Screw the decking down using new screws, don’t be tempted to use the old ones as these will likely work loose.
Before placing your hot tub on the deck, you should use this opportunity to give the decking a fresh coat of waterproofing sealant. There are many wood stains on the market, but as you will be treating the wood under a hot tub, you shouldn’t scrimp on this.
Place the hot tub on the deck.
In most cases, sheer manpower is all that is needed, and two strong people can do this using the right technique.
If your decking is raised 3 feet or more off the ground, you probably have a balustrade around it, and this will have to be removed to pass the hot tub through.
Protect the edge of the decking using sheets of cardboard, bath towels, old rugs, anything you can find. That edge is going to take the full weight of the tub as you lift it onto the deck.
You’re not going to physically lift the tub, just onto its edge, and then you can tip it onto the deck, using its own weight to maneuver it.
To get the tub into its final resting place, position rollers under it before you lay it flat on the deck.
Frequently Asked Questions
Can a wooden deck support a hot tub?
A wooden deck that was built at ground level or just above ground level can support the weight of a fully-loaded hot tub. However, if it is more than 2 feet off the ground, ensure that the support posts are not further apart than 30 inches, and add more if needed.
As I said above, the taller the deck is off the ground, the more support is needed.
This is the key question, and the simple answer is yes, a wooden deck can support a hot tub if the frame has sufficient strength.
If the wooden deck is built on solid ground, you should have nothing to worry about because the joists to which the decking is fixed are continuously supported along their length.
However, if the deck is raised, you will have to do some investigation.
Many recommend placing a hot tub on concrete, and there are good reasons for this, but in a recent article, I explained the various options for providing a solid, stable base other than concrete.
Read it here on my website by clicking on the link.
So, let’s assume the hot tub, when full of water and people, weighs around 4,000 pounds (see my example below).
We need to work this out in terms of pounds per square foot or psf. The reason we do this is that the load capacity of your deck, just like the floors in your home, is measured in psf.
Hot tubs are usually measured in inches, so to get the area in square feet, you need to divide the length x width by 144.
Assuming our 4,000 lb hot tub measures 80” x 80”, this equals 6,400 square inches, ÷ 144 = 44.44 square feet, and 4,000 lb ÷ 44.44 = 90 psf. To give you some perspective, most floors in your home are designed to take 30 to 40 psf.
So, this leads us on to the next question.
Reinforcing deck supports pic.twitter.com/y8xy7MUfAA
— Gross Ridge Outdoors (@GrossRidge1) October 8, 2014
Do I need to reinforce my deck for a hot tub?
A deck that is more than 2 feet off the ground will need to be reinforced to support the weight of a fully-loaded hot tub. But a deck built at or slightly above ground level should be fine to support the weight of a hot tub.
But to be safe, always consult an engineer or building contractor.
If you already have a deck you will want to know if it’s strong enough to take a hot tub. In a recent article, I explained how to determine if a deck can support a tub filled with water and people, and you can read that here on my website by clicking on the link.
Before going any further, there is a number I want you to remember. It is 720, and if you work out the size of your tub in cubic inches and divide by this number, you get the amount of water in gallons.
This will come in useful in all kinds of ways going forward.
So, back to the question, assuming you have a raised deck, you will almost certainly have to reinforce it to take the weight of your hot tub.
You may think that a smaller hot tub is ok, but let’s look at this.
An average 4-person tub measures 60″ x 70″ x 30″ so divide this by 720, and you get 175 gallons. A gallon of water weighs 8.35 lb, so the total weight of water alone is 1,461 lb.
Add the weight of the tub at 375lb and 4 adults at, say, 740 lb, and you have a grand total of 2,576 lb. Divide this by the area in square feet (60×70/144), and you get 88 psf.
That’s about the same psf as the 6-person hot tub. The reason for this is that, although the 6-person tub is heavier, it is spread over a greater area, and it is this that matters.
So, to answer the question, yes, if the deck is raised off the ground by more than 2 feet, you will have to reinforce it.
For how to do this, read on.
How heavy is a 6-person hot tub?
The average weight of a 6-person hot tub, including water and occupants, is just under 4,000 pounds. Empty, the tub will be approximately 675 lbs.
Working out the weight of your hot tub is a simple enough matter, and you can get some general advice on this from a recent article here on my website.
Just click on the link to read it.
You can look at the quick guides in that article, but if you’re looking at a particular tub, it’s best to work out the weight yourself.
There are three elements governing the weight of the tub when full:
- The weight of the tub when empty
- The weight of the water (dependent on the number of gallons at full capacity)
- The weight of the people using it
The first two are standard for each model, but the third is a bit of guesswork.
The weight of the tub when empty is usually provided by the manufacturer, but let’s take an average acrylic tub at 80” x 80” x 34” with a weight of 675 lb.
The number of gallons this will hold may also be provided by the manufacturer, but if not, use this simple formula:
L” x W” x D” ÷ 720 = Volume of water in gallons
Try this using 8.35 lb as the weight of water per gallon: 80 x 80 x 34 ÷ 720 x 8.35 = 2,523lb
Next comes the tricky part—the weight of the people in the tub.
Let’s assume you’re an average-sized family of six weighing in at 200 lb for a male adult, 170 lb for a female adult, a couple of teenagers at 100 lb each, and a couple of smaller kids at 50 lb each, making a total of 670 lb.
Add this to the weight of the full hot tub, and you get 3,868 pounds.
Where do you put a hot tub on a deck?
A hot tub can be placed anywhere on a deck but may need reinforcements underneath. But ideally, ensure that the outer edges of the hot tub sit over the support beams underneath.
As additional supports will almost certainly be needed for a raised deck, this gives you scope to position the hot tub pretty much where you like.
When selecting the best position to suit you, think about the layout and what you want around your hot tub.
- Do you need access all around?
- Do you want space to store the lid?
- Will you be using a cover-lifter?
- You may also want the best orientation for a great view across your yard or to catch those sunsets
Another consideration is where you can physically place the additional supports. On sloping ground, it may be easier to install supports at one end rather than the other.
You should also think about how you’re going to get the hot tub onto the deck.
A 675 lb tub will take some lifting, but two fit adults should manage to get it onto the deck at the lowest edge, and from there, you can slide it into position.
Joist hangers and coffee…my Tuesday morning pic.twitter.com/6FuSFE8bax
— big chief (@wjmarshall73) March 20, 2018
Will joist hangers support a hot tub?
For supporting a hot tub, joist hangers work on the ones that can be nailed through into the joist. The number of nails into the joist depends on the depth – as a guide, 1 per 2” of depth on each side, so for a 6” deep joist, you need 3 nails on each side.
There are two types of hangers. One sits on top of the joist (top fix) like a saddle, and the other type is fixed to the face of the main support beam or post.
You can use 3” decking screws if you prefer these than nails.
Joist hangers are metal straps that fix to the frame, and the joists sit inside these. Some people use framing anchors in much the same way.
If you don’t nail your joists through the hangers, you have what they call a simply supported joist. If you put weight in the center of that joist, it will deflect or bend, and because the ends are free, they will lift slightly.
If they lift too much, they will become unseated, and the deck will collapse!
If the joists are nailed to the hangers, this stops the ends from lifting, which in turn limits the amount of deflection. This makes the floor much stronger and able to take greater loads.
— West Coast Deck Waterproofing (@WestCoastDeck) July 25, 2016
Does composite decking hold up better under a hot tub?
Composite decking is a great way to provide a durable and attractive deck surface for an existing deck or a new deck installation.
It is the most common type of decking material used today, and it can hold up well under the weight of a hot tub.
The composite material is designed to be resistant to moisture, which helps it stand up to the heat and humidity that comes with having a hot tub on the deck.
Additionally, composite deck boards are less likely to warp or splinter than other types of wood decks, making them an ideal choice for supporting a hot tub.
The composite material also resists fading from UV rays, so it will look great for years even when exposed to direct sunlight from the hot tub. With proper installation and regular maintenance, composite decks can provide a safe and attractive surface for your new hot tub.
Do you have to remove the deck railings before installing a hot tub?
Removing deck railing before installing a hot tub is a good idea for several reasons.
First, it allows for easy access to the hot tub during installation. This makes it easier for the installer to move around and get the job done quickly and efficiently.
Additionally, removing the railing gives you enough room to maneuver the hot tub into place without having to worry about damaging the railing or other parts of your deck.
Another benefit of removing deck railing before installing a hot tub is that it allows you to make any necessary adjustments or additions to your deck in order to accommodate the addition of a hot tub.
This could include adding additional support beams or reinforcing existing ones in order to ensure that your deck can handle the weight of a full-sized hot tub.
Finally, removing deck railing before installing a hot tub is often the best option if you want to ensure that your hot tub installation goes smoothly and without any issues. By taking this precautionary step, you can rest assured that your hot tub will be properly installed and ready for use as soon as possible.
Also, before you put those deck railings back on, make sure they don’t block the access panels or make it difficult to install a cover lifter for your hot tub cover.
Does the age of my deck matter when holding a hot tub?
The age of your deck does matter when holding a hot tub.
The best way to determine if your deck is suitable for a hot tub is to inspect it for structural integrity. If the wood deck is more than 10 years old, it may not be able to support that much weight.
You should also check the joist spacing and make sure it meets the manufacturer’s requirements for the weight of your spa. If you have any doubts about the strength of your back deck, you should consult a structural engineer before installing a hot tub.
The last thing you want is for your deck to collapse under the weight of your spa.
New deck builds are obviously better as they can be built to hold the weight of portable hot tubs from the get go. But with the right inspection and adjustments, an older wooden deck can work just fine.
Currently have a crane lifting our hot tub into our deck!! FINALLY 😍 pic.twitter.com/Uht0PN8TX7
— Olivia Daumueller (@daumueller) February 13, 2015
How do you prep an existing deck for a hot tub installation?
Preparing an existing deck for a hot tub installation is an important step in the process of adding a hot tub to your outdoor space.
It is important to ensure that the deck is structurally sound and able to support the weight of the hot tub and its occupants. Here are some tips for prepping an existing deck for a hot tub installation:
First, inspect the deck for any signs of rot or damage.
If there are any weak spots, they should be repaired before proceeding with the installation. Make sure that all nails and screws are securely fastened and that all boards are properly aligned. If necessary, reinforce any weak spots with additional supports or bracing.
Next, check to make sure that the deck can support the weight of the hot tub and its occupants.
In the above sections, I cover both weights of various hot tubs as well as how to gauge if additional support is needed. Generally speaking, the higher the deck is off the ground, the more likely it will need additional reinforcement.
If necessary, add additional supports or bracing to ensure that it can handle the load.
Third, make sure that there is adequate drainage around the hot tub area. This will help prevent water from pooling around it and causing damage to both the deck and hot tub over time. Deck boards are typically placed with small gaps in between, and this is usually sufficient for water to drip down in between.
Finally, clean and seal any exposed wood on the deck before installing your hot tub.
This will help protect it from moisture damage over time and keep it looking great for years to come. Make sure to use a sealant specifically designed for outdoor use so that it won’t be damaged by UV rays or other elements in your environment.
By following these steps, you can ensure that your existing deck is properly prepped for a hot tub installation so you can enjoy your new outdoor oasis without worry!
So, now you know what you have to do to place your hot tub onto your raised deck.
Big or small, you will almost certainly have to reinforce the framework of your decking before you do anything else. But once it’s done, you will have years of enjoyment.
Of course, nothing is quite as secure for holding a hot tub as a concrete slab, but with the right preparation and additional support, there’s no reason a wooden deck can’t support a hot tub just fine.
Thinking an inflatable hot tub might be less weight on your existing deck?
You might want to think again! In a recent article, I cover exactly how much weight inflatable hot tubs produce, and the answer might surprise you!
Just click that link to read it on my site.
It’s worth pointing out that while I have owned 4 hot tubs and had 2 of those 4 installed, including having 3 of them on a wooden deck, I am not a structural engineer or general contractor. So my article, while I believe to be thorough, accurate, and well-researched, should not be construed as professional advice. If you need professional advice on the local business code and structural limits of your deck for the installation of a hot tub, you should seek out a qualified professional in your area.
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