A solid flat surface is required for a hot tub.
Installing hot tub on roof deck.
Many builders recommend installing the hot tub so that its edge is 17 24 inches above the decking.
A deck may be able to support the hot tub as well.
This must be installed along with the concrete deck footings of your deck.
For most a slab four inches thick should suffice unless one decides to get a very large hot tub then something thicker should be poured.
Place additional piers or posts including foundations that are at a minimum 1 foot below the frost line at distances of less than 30 inches from the center of one post or pier to the center of the next post or pier below the foot print of the spa or hot tub to be added.
Costs of installing a hot tub.
A concrete slab is effective at supporting a hot tub.
When installing the hot tub it may end up being more expensive to have it placed in a difficult location.
Install decking up to from hot tub to leave room for expansion contraction and slight shifting of both the deck and the hot tub.
Tall decks and hot tubs if the deck level is higher than the top of the hot tub or the deck is built on uneven ground the hot tub is placed on top of the deck.
For spas located on top of a deck stairs are in order.
Most hot tub manufacturers recommend a concrete slab base over other types of bases.
This slab should be at least 4 inches thick and be fully supported from below.
Guests can sit on the rim and swing around into the water more easily.