A hot tub is a great way to relax or entertain any time, any season. Having one on your deck means you can enjoy it when you want. However, hot tub deck framing has to support much more weight than regular deck framing.
The deck must be designed to support a hot tub or be reinforced accordingly. Closer spaced footings, support posts, and narrower joist span and spacing under the spa are common solutions. Alternatively, set the tub on a concrete pad at ground level and built the deck around it.
In this guide, we’ll look at how a hot tub deck differs from a regular deck, different types of decks for a tub, and framing considerations. We’ll make some recommendations and discuss what to consider when building a deck for an outdoor spa. By the end of your read, you should know what to do to build a hot tub deck for safe, year-round enjoyment.
- Can a Wood Deck Support a Hot Tub?
- Types of Decks where Hot Tubs can be Installed
- Hot Tub Deck Framing Considerations
- Practical Recommendations for Spa Deck Framing
- Building a Deck for a Hot Tub
Can a Wood Deck Support a Hot Tub?
A wood deck needs to be designed or reinforced to support the weight of a hot tub. An 8’x8’ tub full of water and people can exceed 7,300-pounds and an inflatable 4-person one about 3,700-pounds. Wooden decks don’t commonly need to carry that additional weight and aren’t designed to. Building a deck for or adding a hot tub to a deck requires a building permit in most areas.
Most wooden decks are built to support between 40 and 50 pounds per square foot. The weight is made up of the dead-load or building material, and the live-load is made up of people and furniture or snow. Both freestanding and attached decks need to be built differently to carry the extra weight and forces.
Types of Decks where Hot Tubs can be Installed
Hot tub installation can be at ground level or raised decks – wooden, concrete, or steel structures, or on pavers or patio stones. They can be sunk fully or partially below the deck surface, or have a raised section built partially around them. Deck design choices are almost limitless and only constrained by the budget.
Ground and Low-Level Decks
Decks built within three feet of the ground can be built to carry a hot tub, or alternatively, built around or beside a concrete pad on which the hot tub sits. Pouring a Code-compliant concrete slab for the spa allows for standard deck construction. Framing members are set back 1 to 2-inches from the tub while decking closes the gap.
The deck can be built flush with the top of the tub, or lower to provide a step up. Tiered or step decking is also an option and provides a variety of access heights into the water.
On the Top of the Deck
Placing a hot tub on a reinforced, Code-compliant wood deck is a common practice. The deck boards are water-resistant and provide a level or near level surface. It is also the outdoor living space that places the spa front and center – or off in a corner – as part of your entertainment options. The deck area that supports the tub is usually framed separately to carry the additional weight, while the rest of the deck frame is for lighter loads.
Getting the Hot Tub onto the Deck
The size and fabrication of a hot tub determine its empty or dry weight. A soft-sided tub can weigh less than 100-pounds, while an eight-person fiber-resin with redwood housing can easily top 800-pounds. Most dealers deliver and install their products, which makes getting the tub onto the deck their problem.
Removing a section of railing and installing diagonal rails from the ground to deck level and relying on muscle power are common install practices, especially for DIYers. The higher the deck level the greater the need for lifting power and safety. Renting a boom truck or small crane can prevent damage and injury and isn’t overly expensive.
Build Deck Around the Hot Tub
Building a deck around a hot tub is a common practice for decks close to the ground and even those further up too. Whether the tub sits on a concrete slab or pavers on the ground, or on a structurally strengthened deck, the main deck can be built around it. Building around the spa allows for standard deck construction and adjusting the height between the deck surface and the top of the tub.
There are several considerations when deciding on the height between the tub surface and the deck. Access to mechanical systems needs to be planned for as maintenance will be necessary. Additionally, the anchor system for many cover lift arms often drops down 20-inches or more, so deck construction needs to address the cover mechanism too. Ease of access and safety also need to be considered.
Trip and fall hazards are more common when the tub surface is slightly lower than the deck surface or several inches higher than the deck. Stepping down into the spa or over a slight elevation can result in or aggravate injuries.
The distance between the spa and railings, railing heights, privacy fences, and connection to utilities also need to be considered. It should be noted too, that the standard height of many tubs is ideal for easy access by sitting on the edge and swinging feet in or out, minimizing risk. It is also easier for older or injured bodies.
Hot Tub Deck Framing Considerations
There are a number of framing considerations that need to be factored into constructing a deck for a spa. Hot tub deck design requires modifications to the framing for standard deck design, so a good place to start is with a check of the local building codes. Identify any structural needs like post and footing size and location, beam size and spacing, joist dimensions, span and spacing, and any alterations to the ledger board.
Know Exact Hot tub Dimensions
The size and water capacity of the tub need to be available for load calculations when designing the deck, especially if the tub sits on a deck. Purchasing the unit beforehand ensures exact dimensions and weight specifications are available for design. It also means there are no surprises with availability, hook-up requirements, or location of access panels.
Take in Account all Hot Tub Clearances
When determining the location of the hot tub, keep in mind that all things mechanical will need maintenance. Some products have access panels on one side, others on multiple sides, so unless you plan to move the tub every time it needs to be drained or serviced, plan ahead. There may also be local ordinances regarding clearances that should be addressed too.
Service panels should have 18-inches of clearance and don’t forget the head and shoulder room if it is under a deck. Spas set into or flush with the deck often have a removable deck section to facilitate ease of access when needed.
Clearances are also needed for mechanical lift arm movement and expansion and contraction due to seasonal temperature extremes. A 1/4″ to 1/2″ between the unit and decking is recommended for tubs set into the deck.
Plan Hot Tub Location
The location of the hot tub is arguably as important as the deck construction. Its location determines where and how the deck will be built, and once placed, most spas aren’t relocated. Access to removable panels for service and space for the mechanical lift arm for the insulated cover to operate also needs to be factored into the placement.
The location of hook-ups to power the pump and heater may affect the tub location and orientation. Shorter distances tend to be more cost-friendly. Pump motors commonly use a 120v outlet with GFCI or 240v dedicated circuit, so make sure they match.
Heat is provided by an electrical or gas heater, by radiant heat lines, or wood-burning stove. Running a new circuit and gas or radiant lines to a new location adds to the cost, so plan accordingly.
Locate the spa to take advantage of the views, trees, and the sun without obstructing views from inside the house. Air circulation is also important to minimize moisture build-up and dissipate any chemical fumes. Access to the home for cold weather use and lighting are important too.
Neighbors may be welcome guests, but privacy is nice too. Hot tub location and deck design may include privacy screens, an enclosure, pergola, or other considerations.
Prevailing winds are another consideration when locating a spa. Chilly winds circulate around building corners and can decrease enjoyment and increase heating costs. Tubs near the middle of the house tend to feel less wind. Alternatively, privacy structures also act as windbreaks.
Many Building Inspectors and even contractors recognize that small hot tubs tend to be replaced with larger ones. They often encourage homeowners to build reinforced decks to meet larger loads. The load hot tub decks support includes the empty or dry weight of the model selected, the weight of the water, and the weight of the occupants.
The height and diameter or length and width affect the water capacity and the number of people a spa can accommodate. A 29” high by 4’ square tub may hold 165 US gallons, while a 42” high by 8’ can hold 1,075 US gallons. At 8.34-pounds per gallon, that’s 1,371 pounds vs 8,965.5 pounds respectively; an enormous difference when building a deck.
To calculate the load the deck will need to support, add the weight of the empty unit with the water weight and the weight of the rated number of occupants with an average weight of 185-pounds per person. Determine the square footage the spa occupies and divide the total weight by the area to identify the live-load weight factor per square foot. A deck is often built for live-loads of 40 to 50psf, a hot tub can significantly increase that load.
Here are two examples:
A 4-person 29” high by 4’ square spa holding 165 US gallons, occupies 16 square feet
- Empty weight = 120 lbs
- I65 gallons x 8.34 lbs/gallon = 1,371 lbs
- 4 people x 185 lbs = 740 lbs
- Total weight = 120 + 1,371 + 740 = 2,231 pounds
- Load calculation: 2,231 ÷ 16 = 139.4psf
An 8-person 42” high by 8’ square spa holding 1,075 US gallons, occupies 64 square feet
- Empty weight = 1,120 lbs
- 1075 gallons x 8.34 lbs/gallon = 8,965.5 lbs
- 8 people x 185 lbs = 1,480 lbs
- Total weight = 1,120 + 8,965.5 + 1,480 = 11,565.5 lbs
- Load calculation: 11,565.5 ÷ 64 = 180.7psf
The Height of the Deck
The deck height determines the size of posts required to support the deck and other structural requirements identified in the building codes. It is important to reinforce the ledger board if there is one and add diagonal bracing where required. Another impact of the height is getting the tub up onto an elevated deck. Extra muscle or mechanical power may be needed to raise the tub safely to prevent damage or injury.
Deck Framing Expansion and Contraction
Temperature extremes and moisture not only affect people; they impact structures too. The expansion and contraction of wood, plastic, and metal are well known and need to be considered when building a deck. Hot tub deck framing needs to address the issue of potential shifting due to temperature fluctuations to prevent damage or structural failure.
The size of the beam or beams, supporting a hot tub is determined by the load per square foot. A 2 or 3 ply 2×8 beam can support the load if supported every 30-inches, however, a thicker dimensional beam or steel beam will require fewer support posts and footings. Check the local Building codes or with a structural engineer to make sure the design will carry the load.
Joist Size and Spacing
Joist size and spacing for non-hot tub decks commonly are 2x6s spaced on 16” centers. The spacing to support a spa is usually 12” centers and joists may increase to 2x8s or greater. If attached to the house with a ledger board and using joist hangers, additional lag screws are necessary, and possibly a wider ledger and bigger hangers too. It is recommended that a structural engineer be consulted when designing, or redesigning a deck for a hot tub.
While a 4×4 may be acceptable, 6x6s are recommended for decks up to 6 feet off the ground and 8x8s for heights greater than that to carry the additional load of a hot tub. The posts support the beam and transfer the load to the footings.
Reinforced concrete footings need to go to bedrock or 1-foot below frost level, whichever occurs first. The size and spacing between footings depends on the beam dimensions, joist span and spacing, and the load. Deck builders frequently access a structural engineer for specifications and drawings. Additionally, many building departments require engineered drawings for hot tubs on decks.
How to Get a Hot Tub on a Deck
Getting a hot tub onto a deck can take some imagination and a lot of muscle, or the outlay of cash for some mechanical assistance. Empty spas range from less than 100-pounds to more than 1000-pounds, with some closer to 1800-pounds! Moving a unit to a ground-level deck or pad, or near-ground decks may be done with trollies or rollers depending on the landscape.
When installing a hot tub on a raised deck or moving it over uneven or sloped ground, we recommend relying on professional installers. They have the equipment and know-how to get the job done without damage to the unit or causing injury. They will use a boom truck, forklift, crane, or other means to safely install the spa.
Practical Recommendations for Spa Deck Framing
Hot tub deck framing recommendations are many and can range from leaving it to the professionals to just add some extra support posts and a few more joists – Not very helpful. Most building departments require engineered drawings for hot tub decks, especially elevated decks, which identify post location and size, beam dimensions, joist size, span and spacing, and even decking – Very helpful. So, for us, practical recommendations need to be useful.
Ground Level Deck
Ground-level decks or those no higher than the top of the hot tub, don’t need the spa on them. It may be more practical – and less expensive – to leave the tub on the ground and build next to or around the tub.
Building the deck so the top of the spa is 16” to 18” above the deck boards is common. It leaves access panels accessible and makes it easier to get in or out of the tub.
Pour a 6” reinforced concrete slab on a gravel base with the finished concrete surface several inches above grade. The slab should be 6” wider than the tub for repositioning and to support accessories. Although a 3-1/2” pad is acceptable for small spas, the thicker pad or footing handles the weight and seasonal temperature fluctuations better.
When building around or next to the spa it is best to have it in place first. Exact measurements for the tub are essential. Keep the joists and beams an inch from the sides of the tub to allow for some movement and removal if necessary.
Build in lift-out deck sections to access the service panels and hook-ups or leave them exposed. Mechanical lift arms for insulated covers also require space to move. Check the required clearances and build in space for them. It’s easier to build for them than to retro-fit afterward.
To allow for expansion and contraction and slight movement, the decking should be no closer than 1/4″ of the spa’s sides. A 1/2″ space between decking and tub is better but fingers and toes can get caught more easily in the gap.
For uneven ground or decks higher than 3-feet – the top of the spa on a concrete pad – or if a slab isn’t possible, it is more practical to place the hot tub on a deck. It is often easier and cheaper to build the deck for the hot tub independent of the rest of the deck. Always check the local Building Codes for requirements.
Build a freestanding hot tub platform. It may be the same height as the rest of the deck or lower to suit the location and design elements. It should be independent with its own footings, posts, and beams. Joists are commonly independent too but do not need to be if the decking is all the same height.
Ledger boards, joist hangers, 2×8 joist, and 4×4 posts may meet the minimum requirement – BUT – when the safety of family and friends is involved, go big or go home. The cost factor for using larger dimensions when framing a 6’x6’ or 8’x8’ hot tub deck is marginal when compared to the structural integrity it provides.
Begin with 20” footings that reach 12” below frost level or to bedrock. Use 6×6 posts and notch them to support at least two double 2×12 beams.
Don’t use a ledger board or joist hangers when building a hot tub deck. Super-size to 2×10 joists installed on top of the beams and spaced at 12”o.c., 8”o.c. is preferable, though. Use brackets to maintain location on the beam and intermediate blocking for spacing and to prevent twisting.
Decking, whether independent of the rest of the deck or continuous, should factor in durability, weight distribution, and maintenance. Thicker 2×6 decking is more durable and stronger than most other decking, and shouldn’t require painting or staining under the spa enclosure once it’s in place.
Building a Deck for a Hot Tub
Building a hot tub deck is much like building other decks, it just requires more support structure for the additional weight. Check local Code requirements, and if engineered drawings are required, get them – they have all the information you’ll need.
Buy the Hot Tub and Take Exact Dimensions
The exact dimensions are VERY helpful when framing a deck for a hot tub. Buying the tub ensures you have the model you want, and for which the deck is constructed – no surprises. Knowing where all access panels on the spa are located and their dimensions and the location of hook-ups is necessary when planning and framing, especially if the tub will be inset into the deck.
Calculate How Much Your Hot Tub Weighs
The deck needs to support the real load of the hot tub. To determine the pounds-per-square-foot (psf) the deck must support, add the weight of the empty tub with the weight of the water and people it is rated for, and then divide it by the area the spa covers.
A 6 person spa 36” high and 6’ square may have a dry weight of 872 lbs and a water capacity of 495 US gallons.
- weight of water: 495 lbs x 8.34 lbs/US gallon = 4,128. 3 lbs
- weight of people: 6 people x 185 lbs (average weight) = 1,110 lbs
- total weight: 872 + 4,128.3 + 1,110 = 6,110.3 lbs
- hot tub footprint: 6’ x 6’ = 36sqft
- load: 6,110.3 ÷ 36 = 169.7psf
The load the deck under the hot tub needs to support 3 to 5 times the regular load rating for a deck. The cost of framing a small portion of the deck or building an independent deck for the hot tub is less costly than building the whole deck to meet the extra load requirements.
Check Local Guidelines
A review of the local building codes or a call to the building department will often clarify structural requirements. Footing, post, beam, and joist sizing, span, and spacing are required structural information for building a hot tub deck.
Regular decks commonly have joist spacing of 16”o.c., local codes may require 8”o.c. spacing for hot tub decks, doubling the cost of joist and hardware. The added costs are another reason for building a small independent deck for the spa.
Ground Level Hot Tub Deck Framing
Ground-level decks are on or near the ground and offer several options for deck construction.
- Building the whole deck to carry the weight of the hot tub offers greater flexibility when placing the tub but is much more expensive. If planning to upgrade to a larger tub in a few years, the whole deck would need to be built for the future deck load, not the current one.
- Construct a small independent deck that integrates with the rest of the deck. Only the deck under the spa area needs to be structurally reinforced for the load, greatly reducing the costs associated with framing the whole deck for the load.
- Consider placing the hot tub on a concrete slab and building the deck next to, or around the tub. The costs of material and labor for a small deck exceed that of a similar-sized 6-inch thick concrete pad. (Four 20” diameter 4’ deep footings use about 34.9 cubic feet of concrete, a 6-inch thick 6’x6’ concrete pad uses 18 cubic feet of concrete.)
Elevated Deck Framing
An elevated deck commonly refers to one that requires railings and is 30-inches or more above grade. Hot tubs range from 29’ to 42” high with 36” being the most common height. The elevation of the deck could still allow the hot tub to sit on a concrete slab with the deck built beside or around it. If the ground is uneven or a pad won’t work, there are other options.
With the Spa on the Top
- Build the whole deck to the specifications required to support the hot tub. Although that allows flexibility when placing the tub, it’s expensive. Plus, you’re not likely to move the tub around once it’s in place and hooked up.
- Frame the section of the deck where the spa will sit to support the greater load. Install additional concrete footings and posts or piers to support the number of required beams under the tub. Place the joists on the beams, don’t rely on a ledger board or joist hangers. The joists should be level with the joists on the rest of the deck, and may even extend and be part of that deck.
- Construct an independent deck for the hot tub at the same level as the main deck. Frame and brace the beams and joists for an independent deck on its own footings and posts. The joists are independent of the rest of the deck, as are the deck boards. However, the decking may extend and be part of the main deck.
Building a Deck Around the Hot Tub
- Build the deck for the hot tub at a lower level independent of the main deck. The deck will need its own footings, posts, beams, joists, and decking. It may have stairs connecting the two decks, or abut at one or more sides.
- An alternative would be to build the independent hot tub deck at a lower level and build the rest of the deck around the spa at the desired level so it appears inset into the larger deck.
Note: When building a deck around a hot tub, build in lift-out sections or hatches for access to service panels, pumps, and other mechanical components. Additionally, access under the hot tub deck should be fenced off to prevent the risk of injury.
Check the Joist Deflection Under the Tub
One last step when building a hot tub deck is to check the joist deflection under the spa. Joists should always be crown up. As the tub fills with water, monitor the joists – flattening out is acceptable, too much deflection means not enough support.
A hot tub full of water and people can easily exceed 3 to 5 times the load rating of a regular deck. It’s less expensive and often easier to build a concrete slab for a spa and build the deck next to or around the tub sides. If a deck must be constructed, build it independently of the rest of the deck, or as a blend. Reinforcing only the area where the tub will sit will save on material and labor.
I hope you have a better understanding of how to build a deck for a hot tub. If you found this guide helpful, please share it with others. Your comments and suggestions, as always, are appreciated.