Month of January, 1999

Installing A Portable Spa

Part III
Installing an energy efficient spa in the ground.

No matter what is written here, the final authority on construction is your local building officials. Many people want their spa down in the ground, sort of like a natural hot spring.

There are several problems with the old standard way of installing spas in the ground, the reasons I do not recommend installing them that way. The old way is to dig a hole in the ground, and place the plumbed shell (with a layer of foam) directly in the hole.

The problems with it are lack of energy efficiency, and extremely difficult plumbing repairs. The spa tends to float out of the ground after a few years. This style of spa is usually a custom made spa, and is much more expensive per feature than a factory made portable spa.

Because of the moisture in the ground, eventually the (insulation) foam becomes wet, and is useless for insulation. The heat gets rapidly drawn out of the spa vessel.

Any plumbing problems require that the spa be extracted from the ground and this is an all day job for two or three people.

The best way, that I know of, is to install the spa in a vault. This is simply an underground room that is easy to build. It does require a little extra digging and some basic concrete, plumbing, and masonry skills.

You have to plan for drainage inside the vault, similar to the drainage system used in basements.

The proceedure goes like this:

1/ Dig out a vaulted room in the ground, make it at least six inches deeper than the height required for the spa (This is for the concrete floor.) and at least 48 inches bigger than the sides of the spa. If you have a 91 inches by 91 inches by 38 inches high. The hole would be 139 inches by 139 inches by 40 inches deep, figuring on a six inch acrylic rise out of the ground.

2/ Dig out and install the drainage system, either attach it to the house sewer system, or create a drainage system similar to the leaching field used in septic systems. You will need some expert help designing it. Call your building department. Different soils require different length of piping and different sizes of pipe and diferen leach field requirements. The point is to never allow water to build up inside the vault. Put the plumbing for the drain in the corner of the vault.

3/ Dig out for the electrical to be installed, either under the spa or just outside the spa perimeter. Install the conduit, just above the level of the floor 9about 6 inches.
4/ Place a retaining wall made from concrete reinforced blocks (cinder blocks). Use rebar inside the blocks. Because the blocks are 8 inches thick, the room now is 123 inches square. This is 32 inches bigger than the outside of the spa. This allows 16 inches all around the spa for access to the equipment and plumbing.

5/ Using the retaining wall as a concrete form, mark the exact depth of the floor concrete on the wall all the way around the room. Use a laser level or a transit or a hose level to get it perfect. The floor must be level.

6/ Place the drain in position about 2 inches below the level of the floor.

7/ Install a string layout the exact size of the spa at the exact level of the floor, using the concrete wall with anchors to hold the string.

8/ Pour the concrete starting in the center making the area of the spa perfectly level, and the area outside the spa run into the drain, with a 1/4 inch per foot run-off. (If necessary make two forms and pour in two concrete sections. One form for the spa area, and another for the drain area.

9/ After the concrete is cured, place the spa in the vault and have your electricity hooked up. A crane or boom truck works well for lowering the spa in place.

10/ Now build a removable ground level floor decking out of pressure treated and redwood. If you want a planted area around the spa top, you use a 6 inch planters with a plastic liner and place it on a six inch lower decking. Make sure the decking can support the dirt. You can be creative with this. Make it so the planters can be lifted out without harming the plants.

Make an easily accessible door for access to the equipment side of the spa.

By installing your spa this way, you will have a very efficient and much easier to live with spa. If the spa ever has a problem it can be repaired without tremendous effort. The spa will have more efficiency than an above the ground spa. The vault creates another level of insulation, and keeps water off the spas insulation. This is the best in-ground spa installation I know of.