How to Reinforce a Deck to Support a Hot Tub

A hot tub on a deck

Decks come in all shapes and sizes. From a small square landing pad outside the back slider to expansive multi-tiered, multi-functional space, one thing they all have in common is the welcoming draw for a hot tub. Hot tubs, however, are very heavy, especially when filled with water, and chances are that your existing deck can’t safely support it without additional reinforcement. Fortunately, reinforcing your deck in preparation for a hot tub is a relatively easy task. Here are some pointers to help you out.

Step 1 - Collect Your Materials

Wood plank with measuring tools

The size of your hot tub will determine the length of the 4x4s that you mount beneath the deck. Make sure you have enough boards for two supports the same size as the the diameter of the hot tub. You will also need 4x4 lengths long enough to connect the bottom of the deck to the ground. For flat ground you will want four foundation cinder blocks. For uneven ground, you may need to use bags of concrete instead.

Step 2 - Remove Decking Boards if Necessary

If your deck is low to the ground and you are unable to access the underside, you will need to remove the decking boards in the area you plan to place the hot tub. For elevated decks with access underneath you can skip this step.

Step 3 - Cut and Mount the Supports

Cut two lengths of 4x4 to the approximate length of the hot tub. Mount the 4x4s perpendicular to the existing joists beneath the deck. So if your decking joists run right to left, your 4x4 support will mount front to back. You can mount them using metal hangers made for this purpose.

Step 4 - Place the Footers

A deck with missing planks

Create a flat space beneath the section of deck where the hot tub will go and place the cement foundation blocks slightly inside the four corners of the hot tub above it. You will then run 4x4 posts from the 4x4 supports to the cinder blocks, cutting them to length. Mount the posts to the support with brackets. If your ground is uneven, use freshly mixed concrete instead of cinder blocks. Dig about a three-foot hole for each post and anchor the bottom into the cement, ensuring that it runs straight up to the decking support before it sets.

Step 5 - Put it Back Together

If you had to dismantle parts of your deck to add the supports, you can now screw them back into place as you finish up.

One alternative way to create support for a hot tub is to mount the deck to the house. Where it meets into the house, run additional posts from the decking to the ground, flush with the house, on both corners of where the hot tub will sit. This added support will keep the deck from pulling away from the house with the added weight of a hot tub.

Adding additional support to prepare for a hot tub is easy to do. Just keep in mind the main goal of ensuring the vertical posts sit flat on the ground and are plumb with the decking to bear the weight.