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How to Determine if a Deck Can Support a Hot Tub?

For those planning on buying and installing a new hot tub, it’s necessary to put some thought into where it’s going to be installed.  Many people envision a deck surrounding the hot tub.  Some people may even want to place their new hot tub on their existing deck.  This, however, can pose some problems.  Your average deck isn’t designed to bear the weight of a hot tub full of water and people.  For this reason, it’s important to understand how to determine if a deck can support a hot tub. 

And while we strongly suggest that you enlist the help of a structural engineer to do this job, we also think it’s important to understand the basics of such a calculation.  So, we’ve come up with an article to help provide a basic understanding of how to calculate the necessary load bearing capacity of your deck.

Concrete Pad

Hot tubs need to rest on a stable, flat and level surface.  Freshly poured concrete pads are perfect for this kind of job.  However, the thickness of the pad is also important to consider.  For most hot tubs a four-inch concrete pad is sufficient, but extraordinarily large hot tubs may need something thicker.

Existing Decks

As mentioned in the introduction, most decks are not designed to bear the weight of a hot tub full of water and people.  For this reason, if you’re wanting to use an existing deck, it’s important that it’s stabilized and reinforced to be able to withstand its new role.  The fact is that a full hot tub weighs several thousand pounds – many more times than a few pieces of patio furniture and a barbecue.

Required Measurements

To calculate how much weight your deck must be able to support if you want to install a hot tub, you’ll need to know the amount of water the hot tub holds, it’s square footage, its weight and the weight of the maximum number of people you’ll be expecting to use it at any one time. 

Load Bearing Calculations

Getting the weight of your hot tub correct is an important starting point for calculating the load-bearing requirements of your deck.  It’s not good enough to simply use the manufacturer’s specifications as it will normally just give you the dry weight of the hot tub itself.  You’ll also have to factor in the weight of the water it holds and the people using it.  As an example, we’ll assume the hot tub itself weighs 1000 pounds.  If we assume the hot tub holds 420 gallons and a gallon of water weighs 8.34 pounds, your total weight so far would be just over 4500 pounds.  If the tub holds 6 people who weigh on average 200 pounds each (it’s better to overestimate than underestimate!) you’re looking at a total weight of 5700 pounds.  To make the calculation simple, we’ll say the hot tub’s area is 57 square feet.  This means that the deck must be able to support a minimum of 100 pounds per square foot.

Load Support Of Your Deck

To determine whether your deck has the ability to support 100 pounds per square foot you’ll need to enlist the expertise of a structural engineer or get access to the tools, charts, and calculators that allow them to determine the maximum load bearing weight of objects.  In your specific instance, you’ll also need to provide plans or a sketch of the existing deck to show its strengths and weaknesses and where the support beams lie.

Now that you know what to look for when considering installing a hot tub on your deck, download a hot tub buyer’s guide to learn more about installation.