Deck support for spa tub

Do not get to many of these around here so any tips on how to figure proper support for a deck placed unit like in the pictures?
I have more if needed.


Ignoring the railing…:slight_smile:

I can only compare to what I know here Bob… it lacks proper lateral bracing as well as the hardware that would attach the posts to both the concrete piers and the beam. We would use post to beam and post to footing/pier hardware, with the hardware being embedded into the pier/post footing.

Look at page 2 for Pad footing detail and knee brace detail… probably not too much different that your req’s. .pdf link

I would have installed blocking above the beam as well. Spa’s are heavy. Whomever built the deck may not have had the spa in mind.

Bob, one area of deck issues is the connection to the wall and the flashing of same but I’m sure you know that. As an Inspector I would not give specks because you will own it.

From what I can see from these 2 pics I’m sure you can find enough issues to recommend repair and further evaluation by a carpenter that specializes in deck construction.

My concern is not all the obvious deck issues as yes I am schooled on that stuff but on the extra support required as water weighs what about 10 lbs per gallon?
Anyway there is some extra support however as even in this pic you can see it on the right side underneath.
The extra posts mid way towards the home however are outside the Unit .
The posts have been strengthened which I can provide as a closeup and the posts end at middle straight in the earth.
The dark stain was from them BQing down there (even have a built in shelf.)


I have 7 separate issues listed so far and have informed my client by phone that it may be above my skills to calculate this ,but will post my comments here for you guys once I can copy/paste off the final report as I need a PDF to do that in Java.
I am surprised no warm weather guys have responded so far.

Warm Weather guys?
Are you trying to calculate the load Bob?

That deck may be able to handle a typical 40lb live load plus it’s own 10lb build load…

Can it handle 5000lbs of water/spa (5-600 gal spa) and additional people… with the water sloshing around? I think not.

The deck lacks hardware, proper lateral bracing and blocking to begin with… forget the soil capacity and whether or not there are even footings under that “pony wall” to defer the load of the spa above it. As a matter of fact… if those 3 footings were 1sf and the soil capacity was 1500-2000psf (typical #'s) you’d be @ capacity anyway.

Would I endorse it… nope!

OK Tim sounds like you know something and he is going to rebuild it to be larger and two tier so where can I get more info on calculating this thing.
Hmmm lateral bracing? OK makes sense but where are you basing your knowledge from?

Longest home report record on this one.107 pages.
Anyway even though he intends to scratch it here is my comments.

• I recommend a skilled deck builder to calculate the extra load
requirements needed at approx 10 lbs per gallon for this deck.
• Issues that I found include middle support posts having earth to wood
• Posts need to be on footing and also secured with proper hardware to
prevent movement of center of the footings.
• The outside joist connections are toenailed in but I would recommend
hangers like at the ledger board side against the house.
• no flashing at ledger /house can cause Water Intrusion issues
• no risers are a safety issue at the stairs.
• Bottom of handrails should be secured with posts rather than just
balusters .

I’ve built homes apartments etc…

Basically, a hot tub on a deck requires some engineering IMO. The water sloshing about creates complex forces

There could be through-bolting from the ledger to the home and/or in conjunction with additional supports needed at the home and terminal (outer) end. The higher the deck and hot tub are from the ground the more stuff will be needed to be thrown at it.

Lateral bracing… Ok, imagine you are standing at the end of the deck farthest from the home… a poorly braced deck can be shook from side to side just from US dancing or shaking side to side… you’ve felt it on structures before I’m sure. Anyway, even a deck that is reasonably braced that we can not produce any appreciable movement on, is going to have a significant amount of those similar forces placed on it by additional “Live Loads” (people / variable loads / parties) at varying degrees. The movement and stress created by these “Live Loads” will place undue burden/stress on framing members… It’s not hard to imagine a Post that is not Physically connected via Hardware “Kicking Out” causing Collapse of the entire structure… this kind of stuff is what happens when we read about it in the papers.

Anyway, the example I made above (however silly) is COMPOUNDED by the weight and movement of water. Probably more than we can imagine for a small deck structure…

Your buyer should seek consult from a Professional or Structural Engineer.

Or… Put the Hot tub on the ground?

Makes sense as those posts were shifted over near edge of the footings and not bracketed in.
Not sure you can tell in the picture but the deck was shifted towards the side away from the tub.
Guess I will leave that calculation to the pro’s but I consider porches and decks a specialty in training.

You’ll get there! Ya did fine

I woulda made a bit different recommendation… You were certainly trying to and did do the right thing, I hope that is reflected in a positive way Bob, as it should! You didn’t just walk by it and ignore it, it’s a concern and you made light of it, good!

Personally, I would have indicated that the deck had substandard aspects based on it’s current use (addt’l weight) and recommended be further evaluated… You could let the Deck Guy make the call OR make mention of a structural engineer. I would have made mention that I recommend the consult of a Structural Engineer.

As a contractor… they (the engineer) dictate to me how something like this is going to be built.

Tim a typical homeowner likes plain talk and my language reflects that as I hate talking above people in my reports.
Sure I could add tons of code reference and make the reports look like a science paper but that would defeat my purpose of simply adding concerns.

Not sure how others work but everything in my reports actually gets discussed in great detail to my clients on site.
In this case the report is a bucket list for a guy bringing in a crew to remodel and I had detailed everything that should be worked on.
He is replacing the deck anyway but I still am throwing issues in as things for him to notice as contractors are working.

Am I wrong about the weight? I hope not but as for the rest I am not going to worry about the same kind of micro details in calculations as say you would.
The 10 LBS per gallon metaphor is enough to convey the weight(yuck,yuck) of the situation without need to teach deck building 101.

Please explain what you mean by you hope it is reflected in a positive way as that sentence sounds ominous and threatening.
Thanks as I know you mean to criticize in a nice way but I am confused by that statement non the less…

Nope… no spin!

You noted a defect, discussed it with the client so that they understood it and you reported it. That should reflect on you in a positive way.

OK some how I read the first couple sentences wrong.
Just wanted to know nobody thought I made a glaring mistake.


Any loading, span lengths, lumber sizing and connection details not prescribed in the code books will require an engineer for design calculations and details as spelled out in IRC 301.1. The entire deck can be designed with the code books using the standard 40 psf live load and 10 psf dead load except for the area supporting the tub. Water weights 62.4 lbs per cubic foot so 30 inches of water depth will result in 156 psf plus the weight of the tub and deck framework could approach 200 psf. The dead load in the tub area is now 20 times that of the rest of the deck. Basic engineering procedures require the actual dead loads to be multiplied by 1.2 and the actual live loads to be multiplied by 1.6 to provide the necessary safety factors.

I have oversimplified the design considerations to make a point, the liability issues with hot tubs and all other design issues that fall outside the code books is too great. I would recommend a structural engineer if they choose otherwise the liability is on them.

Guess I will disclaimer extra weight calculations from now on

I to will say to recommend a carpenter.
BOB water is 63 pounds per square foot.
A hot tub varies in sizes and normally above 15 SQ. feet.
Now you multiply the gallons by 8.3 if not mistaken and you get a patio that is under rated for that much load.
I see 6/6 that are 2 inches above the ground and surely get wet and wick water when the grass is high.
The center post is a 8/2 and almost off the cement pier or footing.
There is to much going on and I need not see any more photos but to say" recommend a carpenter ".

BOB we all make mistake and you make little.
You are always helpful BOB.
I know you will remember this.