How to Reinforce a Deck for a Hot Tub

A deck is a great way to expand your outdoor space and enjoy the outdoors. Adding a hot tub to your deck can bring a new dynamic to your enjoyment and entertainment. If you’re wondering how to reinforce a deck for a hot tub, we’re here to help!

Most decks will need to be strengthened with additional joists, an extra beam or two, support posts, and concrete footings to support a hot tub. Add proper brackets and hangers if the existing structure relies on toenailing. Also, don’t rely on the ledger to carry the extra weight, or you may damage your home.

In this guide, we’ll explain how to determine if your deck can support a hot tub and what the deck requirements are. We’ll discuss different ways to reinforce a deck for a hot tub, and look at the costs involved. Our aim is to provide you with the information necessary to reinforce a deck for a hot tub.

Can My Deck Support a Hot Tub?

Determining if your deck can support a hot tub involves some calculations. Most decks are rated for a live load or snow load of 40psf (pounds per square foot) and a structural weight typically of 10psf.

So, the support posts and footings are usually designed to carry the combined load of 50psf (40+10). It should be noted, that the age of the deck may affect its strength, so replacing a 15-year or older deck may be advisable before adding a hot tub.

Multiplying the length of the deck by its width identifies the deck area. Multiplying the area by the live load rating provides the design load limit as identified by most building codes. A deck that is 20’ by 10’ has an area of 200sqft.

Multiplying the area by a live load of 40psf, identifies that the deck can support 8,000 pounds spread across its surface. Unfortunately, that only identifies how much weight your deck is rated to support, not necessarily its maximum load capacity.

The problem with the hot tub is that it concentrates the load in a smaller area. A hot tub can weigh between 85 and 800 pounds empty, but filled with water it can weigh between 1,800 and 4,500 pounds or more.

Adding people increases that load even more. Hot tubs range in size from 5’ in diameter for a 2-person tub to 8’x8’ for an 8-person. All that weight is placed in an area ranging from 20sqft to 64sqft, not spread across the whole deck.

Don’t worry, there are ways to calculate if your deck was overbuilt and can support more weight, or if the tributary strength will carry it. Check out my article, How Much Weight Can a Deck Hold to learn how to make those calculations.

It might be easier, though, to consider reinforcing your deck. The great part is that you’re only looking at reinforcing a small area, not the whole deck! However, adding a hot tub to a deck usually requires a building permit, so check with your local Building Department for regulations and guidelines.

Deck Requirements for Hot Tub

Adding a hot tub to a deck isn’t usually a one-step process. The extra weight of a filled hot tub, equipment, and its occupants may exceed what the deck can support. So, the deck may need to be reinforced or the plan altered.

Decks 20” or closer to the ground will often support greater loads than those higher off the ground. The higher off the ground, the more support and bracing required.

The deck should also be stable and level, able to accommodate drainage, access to utility hook-ups, and offer clearance to service motors and other equipment. Wind and seismic concerns may also need to be addressed. You can hire a professional to identify what needs to be done, and then decide if you want to do it yourself or let a pro handle it.

The weight of the filled hot tub and a full load of people, divided by the area of the hot tub’s footprint, identifies the load per square foot. A 2-person hot tub with two average 200-pound adult males in it will have a load of around 110psf while an 8-person with eight 200-pound males in it will add about 95psf to the deck load. The concentrated load is what needs to be supported.

Some solutions are easier and less expensive than others, but even simple solutions can be very difficult. It may be as ‘simple’ as adding extra joists to spread the load or a couple of extra footings, support posts, and a beam under where the hot tub will go to distribute the weight. Sounds simple, but often involves crawling around under the deck and even removing some deck boards. For more information, check out our Hot Tub Deck Framing: The Ultimate Guide.

How to Reinforce a Deck for a Hot Tub

Strengthening an existing deck structure is often cheaper than replacing the whole deck. Adding metal post and beam brackets and connecting joists to beams with hurricane brackets or joist hangers improve its load-bearing capacity.

Identify the type and number of screws or fasteners used to hold structural components together, they can greatly affect load strength. Also, if there is a ledger, ensure it is mounted properly and joist hangers are used.

Consider adding a beam and support posts with footings to carry the additional load instead of the ledger.

Adding an extra joist between existing joists spaced 16” or 24” O.C. is a common way of strengthening a deck. Identify where the tub will be positioned and determine the existing joist spacing and span.

Measure the size and location of existing beams, support posts, and footings in relation to tub location. The dimensions of the tub often determine the length of the additional joists. The other information identifies if more support is required and where to place it.

Check the Deck’s Current Structure

Check the footing size and determine the type of soil and its bearing capacity, this will tell you if you have strong sturdy footings. Soil bearing capacity will range from 2,000psf to 12,000psf, and the diameter of the footing and concrete strength is also important. The depth of the footing should be below the frost line, on solid bedrock, or at least 12” below the top of undisturbed soil.

Check the number of posts and their dimensions – 6×6 posts are stronger than 4x4s. Determine the beam size, span, and location, free-standing or attached, joist span and spacing, use of metal brackets or connectors vs toenailing, type of fasteners used, and species of lumber. All this information will help determine the load capacity of the deck and how best to reinforce it.

Add Additional Support Posts

 

Many factors determine the beam span between support posts. The wood species and dimensions, the number of plys forming the beam, as well as the joist size, span, and spacing influence the location of posts. Adding a post or two between existing posts increases the load-bearing capacity of the beam, which may be all that is necessary.

The tributary area is also affected by the spacing between support posts. Adding intermediary posts decreases the tributary area and increases the load-bearing capacity. However, depending on where the hot tub will be located, this may add too much weight to other support components like a ledger board. Thus, requiring the installation of an additional beam and posts.

Add a Beam

 

Depending on the location of the hot tub in relation to the existing beams, it may be prudent to add one or two shorter beams to carry the weight of the hot tub. The footprint of a hot tub ranges from 5 to 8 feet, so the beam doesn’t need to extend the full length or width of the deck.

It may be necessary to remove some deck boards to facilitate digging and pouring support footings. 6×6 posts with adjustable screw bases will make beam installation and adjustment easier.

An alternative may be to increase the width of the existing beam(s) by adding one or more plys of dimensional lumber. This increased width will increase to load potential of the beam and the related area of the deck. The additional width, however, needs to be fully supported and fastened properly.

Install Additional Joists

Installing additional joists between existing joists spaced at 16” or 24” centers helps distribute the concentrated load of a hot tub. This usually only needs to be done where the hot tub will sit, so will only require the addition of 6 or 7 joists for an 8’ footprint and 3 or 4 for a 5’ hot tub. If joists are at 12” centers, consider sistering instead of splitting the space.

The joists don’t need to be full-length, just long enough to reach support beams and carry the tub. To install the joists, it may be necessary to remove some deck boards, especially if there’s blocking in the way. Alternatively, you may be able to slide them in from one end or another depending on space and access.

The joists should be blocked to prevent twisting under the heavy load and supported by beams, not the ledger board. So, while adding joists will improve weight distribution, one or two beams often need to be added, along with additional support posts and footings. The joists should also be properly attached to the beams with hangers or brackets.

Use Metal Brackets

Use metal brackets like joist hangers, hurricane brackets, post-to-beam brackets, and adjustable screw bases to connect footings to posts. The metal connectors are made of thick galvanized or stainless steel and improve the connection between different support components. The brackets require more fasteners, making them stronger and more supportive, plus the added strength of the steel.

Metal brackets also help prevent twisting and splitting, and help combat uplift forces. They make the deck stronger, more stable, and more durable than toenailing. So, if your deck doesn’t have them, consider adding them or at least use them to reinforce any new components added to support the hot tub.

Use Concrete Footings

Concrete footings provide a strong, sturdy base for a deck. Freestanding decks within 20” of the ground can be supported by concrete deck-post blocks. While the blocks make for a reasonably stable deck, they aren’t as stable, solid, or strong as a concrete footing. Attached decks or freestanding decks higher than 20” off the ground or greater than 160sqft in size, must have concrete or other approved footings.

The size or diameter of the footing depends on the soil strength, the live or snow load requirements, as well as the tributary area. The depth or thickness of the concrete footing depends upon the depth of undisturbed soil as well as the frost line.

Concrete footings must be 12” below the level of undisturbed ground strata, sit on bedrock, or be at least 6” below the local frost level. Footings also usually extend above the grade level by 6”. Additionally, support posts must be centered on the concrete footing.

Use a Hot Tub Pad

An alternative to reinforcing the deck is to use a hot tub pad. The pad may be made of 2” thick interlocking squares of impact plastic, a thick neoprene mat, or another material. They can be placed directly on concrete, gravel, pavers, decking, grass, or even dirt. The base needs to be level and stable, but may be cheaper and easier than reinforcing or building a deck.

The pad can be placed next to an existing deck so it is still accessible from the deck. Depending on the elevation of the deck, the tub may be level with the decking, slightly raised, or lower, but may make access easier.

A hot tub pad protects the hot tub from damage, isn’t permanent, and is easy to install. For more information on hot tub pads and other options, check out my article, Hot Tub Base and Foundation Ideas.

Consider a Separate Platform

Depending on the age and amount of reinforcing necessary to prepare an existing deck for a hot tub, it might be easier to build a separate platform. Remember, the platform only needs to be as large as the base of the tub, so it doesn’t need to be a huge deck. In most situations, only 4 footings need to be dug and poured, plus 4 posts, 2 beams, 6 to 9 joists set, and 10 to 16 deck boards connected together.

Considering that all of those materials, except for the decking, would be required to reinforce most existing decks, the decking is the only extra material. Additionally, 10’, 12’ 14’, or 16’ lumber could be purchased and cut in half, decreasing the amount of lumber and waste.

Most decks are built with a slight slope for drainage which must be adjusted when placing a hot tub. A separate platform could be built level, placed wherever you want it, and valuable deck space wouldn’t be lost.

Cost to Reinforce Deck for Hot Tub

The cost to reinforce a deck for a hot tub depends on several factors including ZIP code. The size and condition of the existing deck, its height off the ground, as well as the size and type of hot tub being installed need to be considered.

Reinforcing all existing connections with steel brackets can add up, as can extra footings, posts, beams, and joists. Replacing damaged or rotting timbers can add to the cost too.

A two-person tub with a round footprint of 20sqft can bump the live load from 40psf to 110psf, while an 8-person tub covering 64sqft could increase it to 95psf. The different consolidated loads can impact the size of the footings, beams, and joists, as can soil strength and frost line depths.

Another big consideration is doing the work yourself vs hiring it out. The DIY costs to reinforce a deck for a hot tub could range from $200 or $300 to more than $2500. Hopefully, you have a better understanding of how to reinforce a deck for a hot tub.