How to Determine if a Deck Can Support a Hot Tub

Congratulations on deciding to buy yourself a hot tub!  You can look forward to many relaxing moments with your friends and family in warm, bubbling waters that will soothe away your aches, pains, and worries.  But before you get to that point, you’ll need to decide where to install the hot tub.  Most people envision a hot tub surrounded by a deck, furnished with outdoor furniture and a barbecue.  But will your deck be able to support the weight of a newly installed hot tub?  In this article, we’ll go over some of the calculations necessary for how to determine if a deck can support a hot tub.

That said, we strongly suggest that you get the help of a structural engineer to ensure the proper measurements are made.  If done improperly, the consequences could be potentially fatal.  For that reason, it’s imperative that the right decisions have been made.  But we also believe it’s important to understand the fundamentals of hot tub installation, so in this article, we’re providing an easy way to calculate what kind of weight your deck should be able to support.

The Base

Hot tubs need a level, stable and flat surface on which to rest.  Concrete pads are usually used for this purpose.  But making sure the pad is thick enough to support the hot tub is also important.  For most hot tubs a 4-inch thick concrete pad is sufficient to support an average sized hot tub.  However, if your hot tub is larger than normal, you may be required to use a thicker base.

The Problem with Your Existing Deck

You might already have an existing deck and think you’ll just be able to plonk your new hot tub onto it and be ready to soak.  However, the fact is that most decks aren’t designed to bear the weight of a hot tub that’s full of people and water.  Your average deck typically takes into account the weight of some patio furniture, your family and your friends.  Hot tubs typically weigh many thousands of pounds and could instantly crush your deck when filled.

Measurements Needed for Calculations

To find out how much weight your deck needs to withstand, you’ll need to gather some basic measurements to use in your calculations.  You’ll need to know the dry weight of your hot tub, the amount of water it holds, the square footage of its base and the maximum weight of the people that will be using it at any one time.

Calculating the Necessary Load Bearing Capacity of Your Deck

Once you have all the required measurements, the formula for calculating the necessary load bearing capacity of your deck is actually quite simple.  First, figure out the total weight of the full hot tub.  As an example, we’ll use a 1000-pound hot tub that holds 420 gallons of water.  At 8.34 pounds per gallon, you’ll have just over 3500 pounds of water.  Add the weight of six large adults (better to overestimate than underestimate) at 1200 pounds and you’ll have a total of 5700 pounds.  Divide this total weight by the square footage of the tub and you’ll have the necessary load bearing capacity of the deck.  To make this calculation easy, we’ll assume the hot tub is 57 square feet which means that the deck must be able to withstand 100 pounds per square foot.

Deck Assessment

To ensure your deck is able to support 100 pounds per square foot, you’ll need to refer to beam-design charts, a load bearing capacity calculator or get the help of a structural engineer.  Having a sketch of how your deck is built, including the support beams, will help determine the need for extra support or buttressing.

To learn more about hot tub installation, download a hot tub buyer’s guide.