How to Reinforce a Deck for a Hot Tub: A Homeowner’s Guide

Do you want to add a hot tub to your deck? If so, then you’ll need to check the structure of your deck. They are really, really heavy! In fact, a fully loaded eight-seater hot tub can weigh up to four tons. If your deck is a little old or not reinforced properly, then it’s going to collapse. Not only would this crush your deck, but it could damage your house and injure anyone who is around.

So, let’s have a look at what you need to do to reinforce your deck. If you want a gorgeous deck with a new hot tub, here’s what you’ll need to do:

• Assess your current deck for its load capacity and age to see if it can work for you.
• Consult a professional if you can to review your existing structure and new deck plans.
• Add the correct foundation, braces, and waterproofing to make your deck solid.

That’s the short story. Now, let’s get into the details of each one of these steps. We’ll walk you through the process and you can decide whether to do it yourself or hire a builder.

Step 1: Assess the Current Deck

Before you begin any reinforcement work, it’s essential to thoroughly evaluate your existing deck. This assessment will help you understand the scope of work needed and identify any current issues that need addressing.

• Age of the deck: Determine how old your deck is. Older decks may require more extensive reinforcement or even complete rebuilding.This is especially true for the deck joists, which will bear most of the hot tub weight.
• Overall condition: Carefully inspect every part of your deck. Look for signs of wear, such as splintering wood, loose boards, or rusted hardware. If deck screws are starting to pull out of the wood or showing rust, this is a cause for concern.
• Damage or rot: Pay close attention to areas that are often exposed to moisture, like areas near the ground or around railings. Soft or discolored wood can indicate rot, which will need to be addressed before reinforcement.
• Existing support structure: Examine the underside of your deck. Note the size and spacing of joists (the horizontal supports under the decking), the size and location of support beams, and the number and placement of posts.
• Attachment to the house: If your deck is attached to your house, inspect this connection carefully. Look for a properly installed deck ledger board (the board that connects the deck to the house) and flashing (material that prevents water from seeping between the deck and house).

This initial assessment will give you a clear picture of your deck’s current state and help inform the reinforcement process.

Old deck looking tired? Check out these hot tub deck ideas for some fresh inspiration.

Step 2: Consult Professionals

While this guide provides a comprehensive overview, reinforcing a deck for a hot tub is a complex project that often requires professional expertise to ensure safety and compliance with local building codes.

• Structural Engineer: Hire a structural engineer to evaluate your deck and provide specific recommendations. They will use their expertise and various formulas to calculate the exact reinforcements needed for your specific situation. Their input is invaluable in ensuring your deck will safely support the hot tub.
• Local Building Department: Contact your local building department to understand the permitting requirements for your project. Most jurisdictions require permits for this type of work due to the structural changes and safety considerations involved.
• Licensed Contractor: Consider hiring a licensed contractor experienced in deck reinforcement and hot tub installations. They can help interpret the engineer’s recommendations and ensure the work is done correctly.

Remember, the cost of professional consultation is a worthwhile investment in the safety and longevity of your project.

To properly reinforce your deck, you need to know exactly what it will be supporting. If you already know your hot tub model, then you should be able to find this information easily. Still looking? Make plans for what your deck can support.

• Dimensions: Measure the length, width, and height of the hot tub. This will help determine where it can be placed on the deck and how much area needs reinforcement.
• Weight: You need two weight measurements:
  1. Dry weight (empty hot tub)
  2. Filled weight (including water and the maximum number of occupants)
• Point load requirements: This refers to how the hot tub’s weight is distributed. Some hot tubs have feet or a base that concentrates the weight in specific areas.

With this information, you can calculate the total load your deck needs to support. Here’s a simple version of the deck load calculation formula:

Total load = Weight of deck structure + Weight of empty hot tub + Weight of water + Weight of maximum occupancy

For example, if your deck weighs 1,000 lbs, your empty hot tub weighs 800 lbs, it holds 2,000 lbs of water, and can seat 6 people at 200 lbs each:

Total load = 1,000 + 800 + 2,000 + (6 × 200) = 5,000 lbs

How can you estimate the weight of your deck? A deck can weigh between 10 and 30 pounds per square foot. The best thing to do is consult the deck plans or the builder.

This total load is what your reinforced deck will need to safely support.

For more information, have a look at our article How to Determine if a Deck can Support a Hot Tub.

Step 4: Reinforce the Foundation

Step 3: Determine Hot Tub Specifications

A strong foundation is crucial for supporting the added weight of a hot tub. This often means adding or upgrading the footings – the concrete bases that support your deck posts.

• Evaluate current footings: Check the size and depth of your existing footings. They may need to be enlarged or deepened.
• Add new footings: You may need to add new footings to support additional posts. The number and placement will depend on your deck’s design and the hot tub’s location.
• Ensure proper depth: Footings must extend below the frost line (the depth to which the ground freezes in winter) to prevent shifting due to freeze-thaw cycles. This depth varies by region, so check local building codes.
• Size the footings correctly: The size of your footings depends on the weight they need to support and your soil’s bearing capacity. Here’s a simplified version of the footing size calculation: Footing area = Total load ÷ Soil bearing capacity For example, if your total load is 5,000 lbs and your soil can bear 1,500 lbs per square foot: Footing area = 5,000 ÷ 1,500 = 3.33 square feet This might translate to a square footing about 22 inches on each side (22 × 22 ≈ 3.33 square feet).

Remember, this is a simplified explanation. A structural engineer will provide exact specifications for your situation.

Step 5: Strengthen Support Beams

Support beams are the backbone of your deck’s structure. They transfer the load from the joists to the posts and ultimately to the footings.

• Evaluate existing beams: Check the size and span of your current support beams. They may need to be upgraded to larger dimensions or reinforced.
• Add new beams: You might need to add additional beams to better distribute the hot tub’s weight.
• Use appropriate beam sizes: The size of your beams depends on the load they need to support and how far they span. A structural engineer will use the beam sizing formula to determine the right size: Required section modulus = (w × L²) ÷ (8 × Fb) Where: w = Total load per linear foot L = Span of the beam in feet Fb = Allowable bending stress of the wood

This formula helps determine how thick and wide your beams need to be to safely support the weight without bending or breaking.

• Consider engineered lumber: Products like laminated veneer lumber (LVL) or parallel strand lumber (PSL) can provide greater strength than traditional dimensional lumber.

Step 6: Reinforce Joists

Joists are the horizontal framing members that support your decking boards. They’ll need to be reinforced to handle the increased load.

• Decrease joist spacing: You may need to add more joists to decrease the space between them. This distributes the weight more evenly across the deck.
• Use larger joists: Upgrading to thicker joists can increase the load-bearing capacity of your deck.
• Add blocking: Install blocking (short pieces of lumber) between joists to provide additional support and prevent twisting.
• Use joist hangers: These metal brackets provide a stronger connection between joists and beams.

The joist spacing formula helps determine how far apart your joists should be.

To use this chart:

1. Calculate your total load per square foot: Total load per sq ft = (Deck weight + Hot tub weight) ÷ Deck area
2. Find your joist size in the left column.
3. Move across the row to find the load range that includes your calculated load per square foot.
4. The right column shows the maximum joist spacing for that load range.

Remember to always round down to the next closer spacing for safety, and consult with a professional before making final decisions on your deck reinforcement project.

Step 7: Upgrade Decking Boards

While the underlying structure is most critical, your decking boards also play a role in supporting the hot tub and resisting moisture.

• Consider thicker boards: Upgrading to 2-inch thick decking boards can provide additional strength.
• Choose moisture-resistant materials: Consider composite decking or pressure-treated lumber for better water resistance.
• Ensure proper fastening: Use corrosion-resistant screws and ensure they’re long enough to penetrate well into the joists.
• Plan for drainage: Slight gaps between decking boards allow for water drainage and air circulation.

In addition to making your deck stronger, consider the use of boards. You might want to upgrade to manufactured lumber or think about non-slip boards.

Step 8: Install a Waterproof Membrane

A waterproof membrane is crucial for protecting your deck’s structure from water damage. 

• Choose the right product: Look for a high-quality deck waterproofing membrane designed for use under hot tubs.
• Cover the entire area: Apply the membrane over the full area where the hot tub will sit, extending a bit beyond its footprint.
• Ensure proper installation: Follow the manufacturer’s instructions carefully. Proper installation is key to effective waterproofing.
• Create proper drainage: Ensure the membrane is sloped slightly to direct water away from your house and deck structure.

Decks are always outside, so the wood should be pressure treated and waterproofed anyway. However, a hot tub will bring a source of persistent moisture. That makes a waterproof membrane especially useful.

Step 9: Create a Level Surface

A perfectly level surface is crucial for proper hot tub function and longevity. Hopefully your deck is already level! But if it’s not, then think through how to add shims and spacers to the installation points in your deck.

• Use a long level: Check for any high or low spots across the entire area where the hot tub will sit.
• Add shims: Use cedar shims to level out any uneven areas. Never use pressure-treated lumber for shims, as it can corrode the hot tub’s base.
• Consider a concrete pad: For maximum stability, some homeowners choose to pour a concrete pad on top of the reinforced deck structure. 

If you need a new concrete base or stronger footers, you can use temporary bracing to keep your deck in place while you pour the concrete. 

Step 10: Add Extra Bracing

Additional bracing can significantly increase your deck’s stability and load-bearing capacity.

• Install diagonal bracing: Add diagonal braces between posts to increase lateral (side-to-side) stability.
• Strengthen post connections: Use post caps and bases to create stronger connections between posts, beams, and footings.
• Consider knee braces: These angled braces between posts and beams can provide extra support.

Many decks are built with 4×4 lumber as supports. These are generally going to be more than strong enough. You’ll need them at each corner and in the middle of longer spans.

Step 11: Consider Access for Maintenance

Plan ahead for future maintenance needs of both your hot tub and the deck structure.

• Create an access hatch: Consider installing a removable section of decking near plumbing and electrical connections.
• Plan for pump and filter access: Ensure you can easily reach these components for regular maintenance.
• Allow for structural inspections: Make sure you can access and inspect key structural elements of your reinforced deck over time.

Maintenance can be a little boring, but it’s also really important. If you can’t inspect your deck because you built a wall around it, invisible problems might develop. 

Step 12: Final Inspection

Before installing your hot tub, it’s crucial to have your reinforced deck thoroughly inspected.

• Professional inspection: Have your structural engineer or licensed contractor perform a final inspection of all reinforcement work.
• Local building inspector: Schedule an inspection with your local building department to ensure all work meets code requirements.

Your local municipality could require a deck inspection. Check their regulations to avoid some uncomfortable and difficult conversations with a building inspector.

Regular Maintenance and Inspection

Maintaining the reinforced deck is essential to ensure its longevity and safety. Regular inspections will help identify any potential issues early on and allow you to address them before they become serious problems.

Periodic Checks for Structural Integrity

• Inspect the deck, including the joists, beams, and supports, every few months or after severe weather conditions. Look for any signs of wear, rot, or damage.
• Check the vertical support posts and footers to ensure they remain plumb and firmly in place. Any shifting or instability should be addressed immediately.
• Examine the decking boards for any warping, cracking, or loose screws. Replace any damaged boards and tighten any loose screws.

Tips for Maintaining the Reinforced Deck

• Clean the deck regularly to prevent the buildup of dirt, debris, and moisture, which can lead to rot and deterioration. Use a deck cleaner and a gentle brush to remove any grime.
• Apply a water-resistant sealant to the decking boards to protect them from moisture and UV damage. Reapply the sealant every few years or as recommended by the manufacturer.
• Trim any nearby vegetation to ensure good airflow around the deck. This helps prevent moisture buildup and extends the life of the wood.

By performing regular maintenance and inspections, you can ensure that your reinforced deck remains safe and functional for many years to come. Proper upkeep not only enhances the deck’s structural integrity but also preserves its aesthetic appeal.

Think Again! Maybe a Deck Isn’t Right for Your House

Decks seem like a natural choice. But there are good reasons why you might not want to add a deck to your home. Check out our article Why It’s a Bad Idea To Build a Deck Around Your New Hot Tub.

FAQ

Can my existing deck support a hot tub without reinforcement?

Most existing decks are not designed to support the substantial weight of a filled hot tub, which can range from 3,000 to 5,000 pounds. Without proper reinforcement, the deck could suffer from structural failure, posing significant safety risks. Reinforcing the deck with additional supports, footers, and joists is essential to safely accommodate a hot tub.

How much does it cost to reinforce a deck for a hot tub?

The cost of reinforcing a deck can vary depending on the size of the deck, the materials used, and whether you hire a professional. On average, you can expect to spend between $500 to $2,000 on materials. Hiring a contractor could add additional labor costs, ranging from $1,000 to $3,000. It’s advisable to get multiple quotes from professionals to ensure you get the best value for your investment.

Do I need a permit to reinforce my deck for a hot tub?

Permit requirements for deck reinforcement vary by location. It is important to check with your local building department to determine if you need a permit for your project. In many areas, any significant structural modifications, such as reinforcing a deck to support a hot tub, will require a permit to ensure the work meets safety and building code standards.

Wrap Up

Reinforcing your deck for a hot tub is a complex but rewarding project. By following these steps and working with professionals, you can create a safe, durable structure to support your new oasis of relaxation. Remember, while this guide provides a comprehensive overview, every deck is unique.

At Epic Hot Tubs, we’re here to support you beyond just providing top-quality hot tubs. Our team is always ready to answer your questions, offer advice on deck reinforcement, or connect you with trusted professionals in your area. With proper preparation and the right hot tub, you’ll soon be enjoying your backyard retreat with complete peace of mind.

Want more value? Look at our list of the best hot tubs for the money.

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About The Author:

Manny Brambila

Pool & Spa Expert

Manny has been in the Pool & Spa industry for over 15 years and is considered a pool, swim spa, & hot tub expert. He has been a Certified Pool & Spa Operator (CPO) since 2009 and worked 15 years in aquatic training and development for the largest pool chemical and customer care company. He also has been an outside consultant for the Pool and Spa industry in Chicago, New York and Los Angeles since 2018. In the past few years Manny has become Director of Operations for Epic Hot Tubs with a priority of providing customers with the most reliable information and best service possible.