Planning the proper hot tub pad is an important part of preparing your backyard getaway. If you’re investing in a beautiful, new outdoor spa, you want to make sure it will be well-supported through all its years of use.
We recommend a gravel base as the best all-around hot tub base, particularly if your hot tub will be installed in an area that doesn’t already have concrete or pavers. (Technically, your hot tub should be installed on crushed stone “gravel”, not actual river gravel, which won’t tamp down properly.)
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Can you put a hot tub on a gravel base?
Yes! Gravel makes an excellent base for a hot tub (also an excellent above-ground pool base material). Generally, gravel hot tub pads work best when using a combination of larger crushed rock for a supportive base and smaller landscaping gravel or pea gravel for a surface layer.
Can you put an inflatable hot tub on gravel? (Lay-Z-Spa™, SaluSpa™, Intex™, etc.)
Yes, if combined with a hot tub mat, spa pad, or flat pavers. Inflatable hot tubs should only be placed on a gravel base if there is an extra layer of protection, such as an insulating mat. The gravel provides good support and leveling for the hot tub, while the spa pad provides extra insulation and protects the surface material of the hot tub from damage.
What size of hot tub can a gravel base support?
A properly constructed gravel hot tub pad can support a hot tub of any size. (By “properly constructed”, we mean a hot tub pad with at least 4” of crushed stone and a retaining border to keep the stone in place.)
Gravel pads are one of the most popular shed foundation options. In that capacity, gravel pads regularly support large buildings (including prefab garages) weighing 5,000 to 10,000 lbs. or more! By comparison, most hot tubs only weigh about 2,000 to 6,000 lbs. when full.
What are the benefits of a gravel base for a hot tub?
Gravel hot tub pads have a number of strengths, but it’s the combination of all their benefits that really makes them the best all-around hot tub base.
Support
A gravel base with at least 4” of crushed stone can support nearly the same amount of weight as an equally thick concrete pad. (Plus, the concrete pad will require a layer of crushed stone under it anyway.) Placing stabilization fabric beneath the gravel (more on this below) improves the stability of the gravel hot tub pad even further. As mentioned above, gravel foundations are a popular shed base and they are more than capable of providing adequate support for a hot tub.
Drainage
A gravel base allows water to easily drain away from the hot tub. Whether it’s water splashed from inside the hot tub or rain water accumulated when the tub is not in use, it will all seep through a gravel pad. A well-drained base can also reduce the risk of slips and falls when stepping in or out of your hot tub.
Leveling
A gravel base is one of the easiest ways to level your hot tub. While pavers and synthetic hot tub pads require a pre-leveled area, a gravel base can be built to compensate for the slope at your hot tub site. Gravel pads can level out a variety of grades and be adjusted so the edge of the hot tub meets existing elements like decks or patios. (This also makes gravel pads a great option for other uses, such as gravel fire pit/patio areas in sloped backyards or even adding a gravel area under a deck.)
Cost
A gravel base is one of the most affordable hot tub pads available, especially if your site is sloped. In general, a gravel hot tub pad will cost about ½ or 1/3 the amount for a concrete pad of the same size.
Gravel vs. other hot tub pads
There are several other popular hot tub pads, each with its own set of strengths. Here’s how gravel hot tub pads compare to each of them.
Dirt vs. gravel for a hot tub base
“Can I put a hot tub on dirt?” is a surprisingly common question. The answer, in short, is “No”. A hot tub should not be placed directly onto bare dirt or in the grass.
If the hot tub is placed directly onto the soil, there is a high likelihood of the ground under it settling over time. Plus, the moisture held by the soil will tend to decrease the longevity of your hot tub.
In contrast, a gravel pad is tamped during installation to lock the stones into place. The locked stones will support the weight of the hot tub while still allowing excess moisture to drain away.
Synthetic hot tub pad vs. gravel for a hot tub base
A quick online search for “hot tub pad” returns a variety of rubber and plastic hot tub bases. These products come in a range of configurations, but are most often composed of interlocking plastic squares.
Synthetic hot tub pads can be easily moved, making them a great choice if you can’t make permanent property modifications (for instance, at a rented property). In some cases, they also provide some insulation for the bottom of your hot tub, meaning it can run more efficiently.
The downside of synthetic hot tub pads is that they can only be installed on a perfectly level site. If your preferred hot tub location has a slope, you’ll need to level the area in some way before adding the synthetic pad.
Gravel, on the other hand, allows you to level the site while installing your hot tub base. A gravel pad is also semi-permanent when compared to other options, like concrete.
Pavers vs. gravel for a hot tub base
If you already have a patio with pavers, you may be able to place your hot tub there. If you’re preparing a new site for your hot tub, pavers are a good option if the site is already level.
Pavers are also one of the most aesthetically pleasing hot tub bases. The variety of paver styles available today means you can find a design to match almost any backyard aesthetic.
Unlike a gravel pad, pavers require a perfectly level site. Pavers are not the best option if your hot tub location has a grade. Pavers also require some type of substrate, usually a gravel or sand mixture
Concrete vs. gravel for a hot tub base
Concrete is one of the most popular options for a hot tub pad. It’s super durable, can support a lot of weight, and can be used to compensate for a sloped site. Of course, if you already have a concrete patio, it makes a lot of sense to put the hot tub there.
The main downside of pouring a new concrete hot tub base is the labor and cost involved. Whether you pour the concrete yourself or hire a professional concrete pad installer, it will still be about 80%-200% more expensive than a gravel pad of the same size.
Additionally, you’ll need to make sure your concrete pad is properly reinforced so it doesn’t crack as the hot tub is used. In some locations, a concrete hot tub pad requires a permit since it’s considered a “permanent” change to the property.
Finally, if the concrete pad extends past the edge of the hot tub, drainage could be an issue. You’ll need to ensure that water is not puddling, increasing the risk of slipping and potentially affecting the longevity of your hot tub.
In general, we find that a gravel pad serves virtually all the same purposes as a concrete hot tub pad. And it makes a much smaller dent in the wallet!
Deck vs. gravel for a hot tub base
Whenever feasible, combining a hot tub with a deck is one of the most popular scenarios. In most cases, though, the deck itself does not actually support the hot tub. Usually, the hot tub is built on some other type of base and leveled so it meets the edge of the deck.
It is possible to build a deck to support a hot tub (on a second-floor deck, for instance), but this is a very expensive option. Building a hot tub into a deck requires special engineering of the deck structure and will most likely involve extra permits, inspections, and regulatory red tape.
A concrete or gravel base works well for leveling a hot tub to perfectly align with the edge of a deck.
Planning your gravel hot tub pad
Before diving into the installation of your gravel hot tub pad, it’s a good idea plan your strategy ahead of time. While the process is very similar to installing a shed foundation, we will cover a few hot-tub-specific questions here.
What gravel is best for a hot tub base?
¾” clean crushed stone is the best type of gravel for a hot tub base. ¾” stone is large enough that it will lock together tightly when compacted, providing solid support beneath your hot tub. Because it’s a “clean” stone, it also functions as a drainage bed to keep excess moisture away from the bottom of your hot tub.
Is pea gravel a good base for a hot tub?
Pea gravel alone is not a sufficient base for a hot tub. Because of its size and shape, pea gravel is prone to shifting and doesn’t make a good long-term support for a hot tub. In fact, some folks who have used pea gravel found that it even shifted out of place during the hot tub installation.
With that said, pea gravel can provide a very nice aesthetic finish on top of a larger structural gravel layer. If you enjoy the look of pea gravel, you can add 2”-3” of it on top of the primary stone base that supports the hot tub. Consider adding the pea gravel after the hot tub is placed.
Alternately, laying a border of pavers around the hot tub can provide a nice finish if you don’t like the look of plain crushed stone. You can even combine pavers with pea gravel to create a pathway around your hot tub.
How much gravel do I need for a hot tub base?
You will need 1 ton of crushed stone for an 8×8 gravel hot tub base on level ground. That does not include adding a layer of landscaping gravel or pea gravel on top.
You can use the following formulas to determine how much gravel you need, both in cubic yards and in tons. The formulas are based on measurements taken in feet.
(length x width x depth)/27 = cubic yards of gravel needed
cubic yards x 1.4 = tons of gravel needed
Using our example from above, an 8×8 pad with gravel 4” deep (0.33’), the formulas would look like this:
(8’ x 8’ x 0.33’)/27 = 0.78 cubic yards of gravel needed
0.78 cubic yards x 1.4 = 1.092 tons of gravel needed
Note: If your site is on a slope, measure the depth of gravel needed at the high side (minimum of 4”) and the depth of gravel needed at the low side. Add those numbers and divide by 2 to find the average gravel depth for the entire pad. (For example, if the high side needs 4” and the low side needs 12”, (4+12)/2 = 8” of gravel on average across the pad.
How deep should a gravel base be for a hot tub?
You will need at least 4” of crushed stone (gravel) to properly support a hot tub. With 4” of stone, there will be enough gravel to lock together to form a solid base under the spa. If your site is on a slope, you can certainly add more than 4” of stone to build up to level (more on that below).
How to build a gravel base for a hot tub
In general, building a gravel hot tub base is very similar to building a gravel shed base. We suggest following our step-by-step guide to building a gravel pad. The main points are as follows:
1. Determine the site slope
If the chosen location for your hot tub is on even a slight slope, you’ll need to build the gravel base to compensate for it. It’s extremely important that your hot tub is level!
That might leave you wondering, “How do I level the ground for a hot tub?”
Basically, you’ll take a measurement at the highest and lowest points of the site to find the difference. It’s easiest to do this with a laser level; you can find a more detailed explanation here.
There are two ways to level a gravel base for your hot tub:
- Build up the low end – This is the easiest option.
- Dig out the high end – This is more labor-intensive
You’ll want to plan ahead if you need the edge of the hot tub to end up at a particular height (for example, to meet an existing feature like a deck or patio). If required, you can even use a combination of digging out the high end and building up the low end.
2. Remove the topsoil
You should remove at least the top 2-4” of topsoil to prevent it from settling once the hot tub is in place. It’s up to you how far above ground you want the finished gravel pad to extend.
To prevent shifting in the future, it’s not a bad idea to tamp down the dirt inside the pad area after the topsoil is removed.
3. Build a lumber perimeter
To frame the gravel pad for your hot tub, we recommend using 4×6 pressure-treated lumber, rated for “ground contact”. This lumber perimeter is what you will use to level the gravel later, so it’s important to get it perfectly level when installing it.
We recommend drilling through the perimeter and running ½” rebar stakes through the wood and into the ground for long-term stability. We also like to fasten the corners with 4” exterior screws.
You can find an in-depth explanation of how to build a gravel pad perimeter here.
4. Add stabilization fabric
While this is an optional step, adding a heavy-duty stabilization fabric before adding the gravel will provide additional support. It will also keep weeds from sprouting up around your hot tub.
We use a woven stabilization fabric with a class 3 rating. More on the type of fabric here and the installation here.
5. Add the gravel
You should have a minimum of 4” of gravel at all parts of the hot tub pad. As mentioned above, we recommend ¾” clean crushed limestone. It should be easy to get it level if you leveled the lumber perimeter properly in the previous step.
Once the gravel is spread and leveled, be sure to tamp it down to lock it into place. You can use a power plate compactor or tamp it by hand. You can see suggestions on leveling and tamping the gravel here.
You can add 2”-3” of pea gravel to finish off the pad if you wish. Then your gravel base is ready for your new hot tub!
As mentioned above, we highly recommend our gravel shed foundation installation guide for a detailed step-by-step overview of the process. With a few minor tweaks, the same process can be used for your gravel hot tub pad.
If installing a base for your hot tub is more than you want to tackle, you can always hire a professional gravel pad company to do it for you! If you’re in our service area (roughly the Mid-Atlantic USA), we’d be happy to give you a free quote on your gravel hot tub base. You can see examples of other gravel pads we’ve built here.
Happy hot tub planning!
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