Outdoor Spa Foundations

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One of the most important things to think about when considering a spa is what are you going to put it on. If you have chosen to place it outside there are many options.

In this article we will discuss these options, so that you will have a sturdy and level surface that is safe for your spa and yourself.

We will cover the options in order of cost and cover the pros and cons of each option as well as that foundation type’s affects on delivering a spa.

Pre Fabricated Pads

Smart Deck Pad

The least expensive option

A SmartDeck Spa Pad or other commercial pads are a great alternative to a concrete slab, and provide an attractive base.

The pads are speedy,  inexpensive, and generally maintenance free.

The pads interlock to make a solid base for a spa. Unlike poured concrete, the base can be easily removed later if desired.

Pads can be combined to make custom sizes. A typical box will create an 8 foot X 8 foot Pad with attractive trim.

Benefits of a Pre-Fabricated Pad

  • Lowest cost
  • Easy to assemble
  • Easy to move
  • Fastest setup time

Drawbacks of a Pre-Fabricated Pad

  • Not as permanent as concrete or stone
  • Ground must be level and compacted

Effects on Spa Delivery

As long as you have a gate wide enough for the spa to enter your yard either flat or on it’s side there should be no challenges with this foundation type.

Stone or Paver Foundations

Paver stones must be leveled and ground compacted to prevent settling.

2nd Least Expensive Option

The use of paver stones or bricks as a foundation can be used as a foundation. This type of decking allows  for many options such as colors, textures, and patterns.

Paver Stones are made by a large number of companies and ultimately give you a wide variety of choices.

Whether you have an existing pad, you have a contractor build one, or are a do-it-yourself person, these stones can make a stylish addition to any space.

The major concern with these is making sure they are properly leveled and that the ground has been packed tight to prevent damage from settling.

An advantage to using this type of foundation is that the rain water will soak through the decking and not pool at the base of the spa.

Make sure to use pavers and not standard bricks as standard bricks may crack and cause issues.

Benefits of a Paver Stones

  • Customizable color and configuration
  • Can be DIY
  • Can be stone or pavers

Drawbacks of Paver Stones

  • Must be leveled
  • May settle causing a loss of leveling if soil or sand isn’t properly compacted

Effects on Spa Delivery

As long as you have a gate wide enough for the spa to enter your yard either flat or on it’s side there should be no challenges with this foundation type.

Decks

Ground Level Deck

2nd Most Expensive Option

A spa can be easily placed on a patio deck or
elevated deck. Make sure the deck is set up to handle the weight of the spa. Especially if the spa is going to be placed on an elevated deck.

Benefits of a Decks

  • Can be a raised deck or ground level
  • Long lasting
  • Customizable shape, style, and color
  • Can run the spas electrical wiring underneath deck

Drawbacks of Decks

  • Must be level
  • Must be engineered to support the full weight of the spa, the water, and occupants.
  • If sunk into deck, the spas side panels must be accessible for repairs & maintenance

Effects on Spa Delivery

Spas placed on a raised deck and spas that are sunk into a deck may require the use of a crane to put into place. 

Sinking a Spa into a raised deck

Building an Elevated Deck
Spa Sunk in Raised Deck

A spa can also be sunk into a deck if you chose. People usually sink their spa into a deck to make them easier to step into.

If you decide to sink it into a deck, make sure that there is still access to the spa’s side panels.

The side panels of the spa may need to be removed in the future for any repairs/maintenance the spa needs.

Can my deck support a hot tub?

Before setting a hot tub on a deck make sure that it can support the weight. You will need a licensed contractor to check to make sure.

The contractor will need to know the outer dimensions of the spa and how much the spa weighs with the weight of the water included.

They can use this information to determine if there are enough supports under the deck and that supports are close enough together to support the weight.

Concrete Foundations

Stained Concrete Deck

Most Expensive Option

A concrete slab is the most durable, stable and most recommended foundation for a spa.

While it is the most expensive of the four options shown here it is by no means unaffordable.

It can be formed in many shapes, the minimum thickness we recommend is 4 inches with rebar reinforcements.

A 12 foot by 14 foot slab would be big enough for an 8 foot by 8 foot spa with steps and a coverlift.

If its a new slab your pouring you should consider sloping it to help water drain off of it.

If it is under a patio cover a slope of 1/8 inch per foot will work great.

If the slab is in the open speak with your contractor about a slope between 3/16 and 1/4 inch per foot.

Also be sure to plan the slope so the filter side of the spa is facing down the slope to help the spa maintain its water flow.

Also there are many colors of stains for concrete for decorative purposes that can be applied, an example of a stained pad is in the picture above.

Benefits of a Concrete Slab

  • Permanent and maintenance free
  • Permanently level or at a safe angle
  • Can run electrical through the concrete slab if its done before the concrete is poured
  • Safest foundation for your hot tub because it wont shift
  • Adds value to home as a “home Improvement”

Drawbacks of Concrete Slab

  • More expensive than other options if you need to pour a new slab.
  • Requires rebar for support

Effects on Spa Delivery

As long as you have a gate wide enough for the spa to enter your yard either flat or on it’s side there should be no challenges with this foundation type.

Other benefits of concrete slabs for hot tub foundations

Another benefit of a concrete slab is you can run the electrical conduits through the concrete before the concrete is poured.

This allows you set the hot tub over the electrical so no conduits or cables are visible outside the spa.

This is a benefit both in how it looks aesthetically and for safety.

You can ask us or your local dealer for your spa’s electrical drawing to determine where the optimal place is to bring the electrical wiring up through the concrete slab.

It is highly recommended to have the electrician run an extra 4 to 6 feet (1.2-1.8 Meters) of wire through the conduit to make sure the wiring can reach the spa’s electrical hook up points. 

This will make it easier during the installation and hook up of the spa.

Having additional wire run will also save you money from having to have the electrician run a new wire or add to the existing wire if it was too short to reach the connection points.

A final benefit is this will also help in case the spa needs to be moved or rotated later.

 
 
Stub Outs for electrical
Electrical Conduits & Rebar Being Placed Prior To Pouring The Slab

The pipes sticking up (Stub Out) in the above picture are conduits for electrical lines that will run through the concrete.

The grid on the ground is metal rebar that will reinforce the concrete increasing its strength.

Electrical Stub Out

Sinking a spa into a concrete foundations

Sinking your spa into a concrete slab can be done but it comes with large issues. We do not recommend doing this.

  1. You will need a submersible pump in the bottom of the hole to pump out rain water or in case the spa leaks.
  2. Expensive to Service: You may need to hire a crane to get it out of the hole to service the spa. If a crane is not used it will require a large number of people on site to lift it.

Adding Space To An Existing Patio

If you decide to add on to your patio to allow for additional space for a spa it is highly recommended that you dowel the two slabs together. This is done by drilling holes into the existing concrete slab.

Short lengths of rebar (dowels) are then inserted into the existing slab and tied onto the rebar for the new concrete slab.

This is important as over time the ground will settle and shift and without the dowels in place the two slabs will be at different heights from each other at the joints where they connect. 

Dowel hole drilled
Drilled Hole for Rebar Dowel
Dowels and Rebar
Dowel Rebar In Existing Slab Ready To Conect To New Rebar

Styling A Concrete Slab

Concrete slabs can be made in the traditional smooth style or several different ways. It does cost more but you can also stamp, stain, and seal the concrete.

You can do any combination of these options to alter the look of the concrete slab.

There are tons of stamp options to make the concrete look like stone, wood texture, pebbles, brick, and more.

You can even take the slab style a step further by staining the concrete.

This alters the color of the slab to match the look you are trying to achieve. Lastly if you are looking for a “wet stone look” you can seal the slab.

However, keep in mind the sealant will need to be re-applied periodically to keep the effect.

Smoothed Concrete Slab With Brown Stain
Stained and Stamped Concrete
Stained And Stamped Concrete With Sealant

A Foundation's Load Capacity

Hot tubs weigh a lot when filled. Each gallon of water weighs about 8 pounds.

Which ever foundation you end up choosing needs to be able to hold up the weight of the water, the weight of the spa itself, and a safety factor.

You can use the calculator below to get an estimate of how much your spa will weigh when filled.

Most 8 foot hot tubs hold about 300 gallons. Whereas a swim spa can hold up to 2500 gallons.

You can check online for your spa’s exact gallon specification.

If you choose a foundation type that requires a contractor such as a deck or slab they will be able to help you plan for the load requirement.

Hot Tub Weight Calculator

To determine the load of your spa, use the slider to select the number of gallons that your spa can hold.

Then enter the dry weight of your spa in the box below.

The calculator will then show the weight of your spa with water.

Use this weight to help plan your foundation requirements.

Accessibility For Spa Delivery

Crane lifting a spa

Wherever you decide to put your spa, it is always advisable to check the dimensions of your spa against the size of your gates or doors to see if the spa can be wheeled into place.

Should you decide to place your spa in a place such as: an elevated deck, a location that doesn’t have a gate wide enough to allow access, or in an obstructed area, you may need to use a crane to put the spa into place.

Many shy away from using a crane because of concerns over cost.

The good news is the use of cranes is less than you might think, mostly as low as a few hundred dollars depending upon the job.