On 11/3/2016 2:06 PM, wtf wrote:
On 11/03/2016 01:59 PM, wrote:
I need to figure out how to reinforce the deck. Joists are 12 inches
apart. 4x4s are 15 feet a part one way and 100 foot the other.

You deck joist spanned 12 so figure 100 foot the other 4x4 apart by 15
inches OC plywood span reinforcements configured hot tub?


Not enough info to give you a definitive answer. Are the joists 2 x 6
or 2 x 8 or 2 x 12? What is the weight of the tub with water and naked
occupants?

Once you figure that out you can figure how many 4 x 4 to add, with
proper footings of course. At the minimum, I'd put one at each corner
and one in the center. You may need more.