How to Reinforce a Deck for a Spa / Hot Tub


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When you add a spa or hot tub to a deck you are adding a lot of weight. This "How to Guide" is to show one possibility of reinforcing your deck so that it can properly support the added weight from your spa or hot tub. Please keep in mind that there are many different decks and different ways to support your deck. This is one way that my engineer provided to reinforce my deck for my spa. Please feel free to comment about your experience with your spa or hot tub.

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Step by Step


Step 1

The first step is to talk to an engineer. After adding a spa, plus water, plus people in the hot tub you can add around 6000 lbs to your deck. My spa started off at 600 lbs. The spa filled has 320 gallons or 2672 lbs. (8.35 lbs / gallon). If 7 people sit in my hot tub that is an additional 1050 lbs. (average 150 lbs). That is a total of 4,322 lbs. My engineer informed me that my current deck needed more support even before adding a spa or hot tub. I also hired carpenters to come out and make sure the job was done correctly.

Step 2

My engineer recommended to add an additional joist to each of the existing joist on the deck where the spa would be sitting. He also recommended to add additional Ledger board fasteners to the ledger. Our first step was to knock out the nailed in blocks so we could add the additional beams to the deck.

Step 3

We then added ledger board fasteners to the existing deck ledger. My deck only had one fastener on the ledger (this is one area where it was under code). We added an additional 4 fasteners to each area between the deck joists. Each fastener was 3 - 5/8" long. This was to help support the weight of the new spa.

Step 4

We next placed a new joist butt up against the existing joist. We held the joist in place with a clamp before fastening them together. Adding joists will help distribute the weight for the addition of a spa.

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Step 5

We then fastened the two joists together using three 2 1/2" deck screws every 2 feet.

Step 6

Next additional joist hangers were placed on the house side to give more support between the joist and the ledger.

Step 7

We finally nailed the blocks we took out back in place. The blocks needed to be modified due to the addition of the joist.


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 Posted: 7/21/2019 

What did it cost you?

InyoPools Product Specialist  Posted: 9/3/2013 

decking support - Reinforced deck is working great- three years now. I would double your joists and add extra footing supports. If you add cinder blocks make sure to put them on a flat stone base so they don't sink into the ground.

Anonymous  Posted: 9/2/2013 

Thank you for this information. I am about to undertake the same project. How has this worked for you? I have a five person Gatsby spa. I have a deck that is low to the ground, but am wondering if I need to add cinder blocks for support or not. Maybe I need to double up my joists too - mine are 16" on center 2x10s. The deck is on concrete footings. Any suggestions? Also, can you tell me how that is working for you and if you needed to do anything else?? Thanks!

Anonymous  Posted: 3/4/2020 

2x10? I dont think you need to do anything