On Ground installations

The first rule for on ground installations is that you do not want to just level a piece of ground and put the tub on it. Even with the 4 x 6 chine joists supplied, the tub is only a little over two inches off the ground. Water sloshing over the tub from getting in and out and rainwater runoff will cause dirt to splash up on the bottom of the tub as well as the staves.

The acids in the soil can cause the wood to rot. Most woods commonly used for hot tub construction (Western Red Cedar, Redwood, etc.) have properties that are highly resistant to rot caused by contact with water, but the acids in most soils will quickly deteriorate even the most rot resistant species.

Accordingly, you will want to design a supporting base that is, at minimum, one foot larger than the tub.  If there is room, a two foot buffer or more is even better as it will provide more room for access and walking around the tub. If there are additional cedar accessories like surrounds or stairs, you will want to design the base to include them along with the minimum one foot buffer area.

For on ground installations a concrete pad is ideal. If the bed is properly compacted and the surface level you should have a stable platform that will last the life of the tub. The pad itself should be at least 4” thick and reinforced with mesh to control (not prevent) cracking.

A 4″ thick reinforced concrete pad is a standard concrete driveway construction and is rated to hold 8,000 pounds.  You can certainly go with a thicker slab, but 4″ should be adequate for all except the very largest tubs.

If you will be putting in a concrete pad, give some thought to the need/desire for access and companion amenities such as chairs, a little table, etc. You may want to make the pad significantly larger than the basic footprint of the hot tub to accommodate such items.

There are many other types of satisfactory on ground bases that can be installed although they lack the permanent stability of the concrete pad. Many owners have opted for a gravel (crushed river rock) base, typically surrounded by railroad ties or other treated lumber. The basic approach is to dig a pit of appropriate size about 12-18 inches deep and fill it with medium size crushed river rock. A refinement is to use crushed rock in combination with sand to fill the pit, as it will compact better and be more stable.

This type of base will almost certainly settle over time, but it is easy to re-level and can conveniently be done when the tub is emptied for cleaning. Other on ground bases to consider are concrete pavers and patio blocks.