There aren’t many people who don’t dream of having a fun and relaxing hot tub in their backyard, but not everyone has the perfect place to install one. In this brief post I want to go over what will, and will not work as a base for your new portable spa.
The Weight of Water:
Before we get into the materials we use for a hot tub base we need to first understand the characteristics of a portable spa filled with water.A hot tub dry just delivered to your house only ways a few hundred pounds and on its own could sit just about anywhere. The problem arises when you fill the vessel up with water, this makes a few hundred pound tub a few thousand pound tub…water is HEAVY!
The weight of the water is producing a lot of force onto that shell, thus the most important part of placing a tub is making sure it is 100% completely level. If the level of the spa is off the force of the water will cause the shell to stretch and warp over time, and this can cause serious damage to the unit.So how do we make sure our beautiful hot tub does not warp and crack? Use the proper materials and construction.
Placing a hot tub on a deck
Watch our new video: “Can I put a Hot Tub on a Deck?”
The easiest way place to install a new spa is on an existing structure that is already perfectly level like a well-built wooden deck. People often worry about the structural integrity of their deck and if it can support the tremendous weight a a full hot tub. It is a valid concern but what we have found is that most any built to code deck is plenty strong enough to support a hot tub.
If you have a standard wood deck with 2”x8”’ joists 12” off center with proper supports you are good to go. Even though the spa weighs up to 4,000lbs full when it is level the weight is evenly distributed over the bottom surface area of the tub at about 100lbs per square ft. This even weight distribution allows the deck to support the weight easily.
Existing Ground Level patios
A lot of times when we sell a hot tub the customer already has an existing ground level patio, made of concrete patio blocks. Just like a deck this works great for the customer as no additional construction is needed. Unfortunately a lot of these patios are pitched for drainage or have just buckled over the years and become un-level. If a slight pitch is found where the tubs is going you can get away with using some wooden shims to make sure the tub and water is level.
Paver Patio Installation
As we do a lot of paver patio installation we have recently been doing a few patio hot tub projects. Using a solid base material we install a complete concrete paver bloc patio using products from Techo-Bloc. Generally this patio is much larger than just the hot tub base and we make sure the area where the spa is placed is perfectly level and then pitch the patio of rain run off after the spa area.
Poured Concrete Spa Pad
When neither an existing deck or patio are useable for your new hot tub a lot of times the best option is a poured concrete pad. A concrete pad is great because you can get it to set perfectly level and it creates a nice solid base for the spa.
We recommend pouring your concrete slab 3-4” thick using a 2”x6” wooden frame to create your form. If it is not a project you want to take on yourself here at Precision we can provide the pad installation for you.
Placing a Hot Tub on Crushed Stone
A simple an inexpensive way to prep the ground for a new spa is by using a crushed stone base. While not the prettiest or the most solid base it can work if done properly. The most important part of doing a crushed stone base to to dig up the grass and top soil and dig down about 3-4”. Try to level the ground a much as possible but it does not need to be perfect at this stage.
You then want to run a couple of 4”x4” stringers completely level across the area spaced about 4’ apart. This will give you something solid to set you level. You can now fill the area with 4” of crushed stone, make sure the area is about 4-6” bigger than the spa itself. Pack the stone down and level it as much as possible.
When you set the tub on the crushed stone the weight should allow it to settle into a level position with the 4×4 stringers helping.
A Prefabricated Spa Pad
Finally another available option is a pre-made plastic spa pad. These usually come in kits that you buy to fit your size spa.
The misconception is that these pads require no site prep which is completely false. You need to prep the space just like you would the crushed stone pad above. Dig up the top soil and level it out before you put the pad down and place the spa.
It is very important to take your base into account when planning for a new hot tub at your home. The good news is we can help you every step of the way, even do a free at home consultation to help find the best place to put it and what material will work best for your yard and budget.
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I was given a hot tub by a friend who needed the space it was in. They were not using it and it was setting in the garage. I put it down on my concrete back porch. There is no roof over the porch and the concrete has some low spots where some water will stand. Do I need to get the base of the tub off of the concrete where water stands or will it be ok just setting on the concrete. The standing water is not deep. Maybe not standing water at all, just very wet.
If water is standing there than the pad is not level. If the pad is not level when you fill it with water the weight of the water over time can crack the acrylic shell. The most important thing is that it is perfectly level. If you need to shim it to make it work in that spot that is fine.
My tub is almost 2″ lower in the front than the back. Can I simply shim the front of the tub to make it level?
If you absolutely have no other option to redo the base then yes shim the low side, you do not want the shell warping or cracking.
Can I do cement blocks on the peripheral and gravel in the center for a temporary pad?
First off thanks for checking out the blog!
The MOST IMPORTANT THING about a hot tub base is that the ENTIRE base is supported and it is level. So, in your case what I would do is create a crushed stone box. Rather than put cinder blocks on the edges use 4×4 or 6×6 pressure treated posts. Create a box and add an additional post running down the middle. Then fill that box with 3/4 stone and pack it down as best you can. Make sure the compacted stone is at the same level as the wood posts.
Now you have a base that supports the whole spa equally and the stone won’t settle and be pushed out as you created a box to hold it in.
Hope that helps!
I have a pad from a previous owner’s hot tub, we are about to do a large Flagstone patio addition and are considering keeping the pad to put a hot tub on there down the road. My question is: would it be better to keep the unsightly pad vs putting in a 1.5-3″ flagstone patio in its place w/ ~6″ crushed stone base. Obvious concerns are the natural nature of the stone wont be as easy to level, but should I be concerned with the weight?
I definitely wouldn’t do flagstone under a hot tub. You are right, too hard to get perfectly level and smooth so the whole base is supported evenly. I would just keep the pad, do a decorative crushed stone around the perimeter of the spa to cover up the edges of the concrete pad, then do your flagstone.
Hi hope you can help me, I am just about to purchase a hot tub, originally I was going to have it on my patio which is block and beam. My
understanding is when the hot tub is full of water it will weigh about 2 tones , I don’t think my patio will take the weight. At the weekend I purchased some rubber square mats measuring 400 x 400 thickness 25mm.
Can I just level the grass area and then put the mats down – with the hot tub on top. ..I don’t want to put a concrete base in really. I would like to be able to move it if I want to.
Would you say otherwise it would be better using concrete slabs.
Your deck will probably support it. The spa displaces its weight evenly at about 60-70lbs per square ft. Most decks are built to hold 100lbs per square ft.
You can use a temporary base but it is IMPERATIVE that the ground is PERFECTLY LEVEL, and I mean DEAD ON level before you place the hot tub down. You do not want to risk cracking the shell.
Could you please advise me in Regards to Weight distribution ,I would like to know is Weight supported by the frame only or does the bottom (lowest part) rest on the floor surface ??
It does depend on the base of the spa but mostly you have an outer frame with cross supports the evenly distribute the weight. This is why the entire base of the spa needs to be supported.