Hi y’all – got the joist calc part okay for normal loads, but current prospective client wants to know if hot tub would be okay in future. Deck, 2×10’s, 12′ span, would/could it hold a hot tub in future? (Say 4 person tub). Thanx for any help.
Let’s not confuse the issue with facts!
Replies
Normal loads are one thing and a hot tub is not in that category. Your county will have codes for this and spending a day in the county office discussing this with an inspector will help ease your mind and pocket in the end.
How high off the ground will it be?
The hot tub manufacturer should be able to give you the installed/filled weight of the unit.
"manufacturer should be able to give you the installed/filled weight of the unit."
One would think so, eh?
But recently at a home show, I asked about that at a dispaly booth. I asked what sort of special support it would need...
He replied, "Oh it will be fine over any normally framed deck, as long as there are 2x8s"
Over any span or spacing apparantly.
Not being in a mood to argue, I rolled my eyes and walked off.
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Well, I didn't say to ask the salesman -- I said ask the manufacturer.
A manufacturer's rep is the manufacturer from a legal and practical standpoint.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Good God No! A hot tub requires a whole 'nother order of magnitude of support. Not only is it heavy (fresh water is 62.something pounds per cubic foot), it also moves, unlike a rain soaked snow pack on a roof. The inertial forces involved when shifting masses of liquid slop around inside a tank can be enough to capsize a full-sized ship (this is called 'Free surface effect', if you're curious). Imagine what it can do to a wood-framed deck.
The best installations provide a completely separate support structure for the tub itself, and the deck is built around it (unless it's a retrofit). I'd recommend steel. Get an engineer to design and sign off on it. Then find a good welder....
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Your right about the 62 lbs per cuft. There are 7.48 gals. per cuft and 8.34 lbs per gal which comes out to 62.3832 lbs. If the deck is only a few feet above the grade I would install footings and a beam system to support the hot tub separately. If they are thinking of adding it later it would be cheaper to install the footings now and frame it later.
Edited 4/12/2004 9:22 am ET by Jemcon
You using those undersized US gallons in that calculation there <G>?
Actually, my memory wasn't far off. According to Appendix D in my Merchant Marine Officers' Handbook, (Cornell University Press, 4th Ed., 1965), one US gallon is 231 cu. inches. One Imperial gallon is 277.274 cu. inches. An Imperial gallon of SEAWATER weighs 10 pounds, exactly (that may well be how the size of the Imperial gallon was originally fixed at that odd number of cubic inches). 1 cubic foot of seawater weighs exactly 64 pounds.
For FRESH water, which is most likely what you'd have in that hot-tub, the figures are lower (fresh water is lighter than salt water). One cubic foot of (distilled) fresh water weighs 62.35 lbs. It contains 6.232 gallons (US). A long ton (2240 lbs) of fresh water will occupy 1 cubic meter, or 35.84 cubic feet.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
I am in school for my New Jersey "S1" wastewater liscense and those are the number the University of California say are the weights and volumes of water. Thats the format most states follow for liscenseing. If those weights are wrong argue with the scientists in the University of California.
Not planning on arguing with anybody. If California has heavier water than the rest of the world, it ain't gonna ruin my day. Considering they have so little of it to start with, maybe they're just doing a little compensating to avoid psychological traumatization complex....
But when I wrote my license exams for the US Coast Guard for my Master's ticket, that's what water weighed. The figures are based on freshwater density of 1,000 oz. per cu. ft (1.000 specific gravity) and 1,025 oz. per cu. ft (1.025 specific gravity) for seawater.
Since I passed the exams and got my license, I tend to believe these figures are correct. I mean, the Coast Guard does deal with water on a daily basis, if you follow me....
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Let's not have an argument about the combined knowledge of the Coast Guard and the U of Cali.
Do I have to bring up the neither of you are taking into account the curvature of the earth? <g>
Jon Blakemore
Jon--
You ought to know better. It's got NOTHING to do with the curvature of the earth. The curvature of the earth is what makes it possible for you to plot a rhumb line on a flat paper chart. (C'mon, Sphere--jump on that one, LOL!)
The phenomenon you probably meant to mention is the effect of the flattening at the poles--the earth actually being an oblate spheroid instead of a globe--which, of course, causes all sorts of smooth functions to disfunction....
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Now the way I heard it you had to be at least 6' tall to be in the Coast Guard......
So if the ship sunk you could walk to shore..........
I was only 5'10" and had to join the Navy......
hehehee"Rather be a hammer than a nail"
Bob
Well, I'm actually six-one, so I supposed I could have joined the Coasties based on that criterion. But that's metric, of course. Nobody would have me except the Merchant Marine, where one chief mate has to do the work of thirty-seven petty officers, twelve j.g.'s, and a three-stripe commander....Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
>>where one chief mate has to do the work of thirty-seven petty officers, twelve j.g.'s, and a three-stripe commander....
I know you're not counting PO2's, cuz they have to be qualified to do all the above and then some.
SamT ex ETN2
Actually,at the end of my career in the navy, I had a RM1 and an ET1 working for me. And the POQRB wanted to bust me for incompetence. Go figure. ST
ROAR!!!Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Back in my distant past I spent 2 years installing spas for a local company. Spas in a wood deck were very common but we never even considered letting the joist carry the weight. We framed the deck as usual but with an opening for the spa. We then built a separate structure that bore directly on the ground to support the very substantial weight of the spa. We also made sure that the lip of the empty spa was about 1/2" above the deck so that when we filled it the lip wouldn't break.
At the very least, specs will cover empty weight and gallon capacity.
Mine weighs ~400 empty and holds ~350 gallons. 8.3 lbs per gallon gets us ~3300 lbs full, plus occupants and the rubber ducks. A bottle of beer weights a bit over a pound; cans a mere 13oz. :)
I have put it on the decks in two homes, but both had piers under all four corners of the hottub.
Edited 4/4/2004 11:16 am ET by snsteury
put up adeck last summer...attached hot tub room..span was 8' for 2x10's PT..12'' centers. Advantec then wonderboard then tile..tub w/o people was 500lbs empty..still ok as far as I know..
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Repairs, Remodeling, Restorations.
We put one up about four years ago. 2x12 on 12" centers under the tub area, but only about an 8 or 10' span. Works fine so far. Get a good beefy cross beam under the deck, and some extra posts and concrete under the tub area and you probably won't have a problem.
When you put these things on the ground, did you have to consider frost heave? Did you install drainage beneath?
Haha! Neither. I'm in south Florida where the only frost is in the freezer and the ground is sand.
Did I mention that I my next house will be on a Carribean island. Here in Maine we sometimes get frost SIX FEET into the ground! (The last two winters)
I don't like to install Hot tubs on decks for a few of reasons:
1. It weighs about 3500 pounds full of water
2. the circulating pump transmits a hum into the house
3. It is too tall 40" above the deck surface which means you have to eat up
more deck space for entry steps.
Here is a shot of how we support a hot tub....................
"Rather be a hammer than a nail"
Bob
Thanx for all your responses. Sometimes I just want someone else to belabour the obvious to make sure I don't have blinders on. Sure I can encourage them to go with a 'sunken' tub.Let's not confuse the issue with facts!
Nice looking work, there. What's the span and center-to-center distance on those supplemental joists?
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Dino- Those are 8' 6X6 incised pressure treated Doug fir joists 6' span inside to inside on the top.................."Railroad trestle" is what I like to call it"Rather be a hammer than a nail"
Bob
When I saw those pictures I thought a locomotive could sit on that. What are the post holders , 6x6 simpson they look like your weak point on the system? (:
ANDYSZ2I MAY DISAGREE WITH WHAT YOUR SAYING BUT I WILL DEFEND TO THE DEATH YOUR RIGHT TO SAY IT.
Remodeler/Punchout
The Post holders are Simpson PB66 but I would have rather used the CBSQ66 which has a 1" stand off plate underneath..........Right now you cannot get either with the heavy duty Galvanization required for todays ACQ lumber.
Right now I am awaiting an inspection on 22- 3' deep holes for 6x6 arbor posts because I could not get the CBSQ66 or the new G185 hot dipped galvanized bolts for the post bases.........
We are all going to experience difficulties in this transition period of change over to the new hardware for the new wood."Rather be a hammer than a nail"
Bob
Ahh, classic RR trestle design. Very Nice....that's not a mistake, it's rustic
I build railroad trestle forms for deck rails sometimes. There's an architectural detail in Québec that consists of X bars inside the box formed by two posts and the top and bottom rail. (The name doesn't translate well.) I also use the same form for the trusses I build to prevent docks from racking when the pilings can't be driven and are 12' apart sitting on concrete mud floats on the bottom of the lake. We float the trestle-truss out into the lake, sink it with a couple of concrete blocks, tack it in place between a set of legs with my old Senco III, then run 6" lag bolts through into the pilings. They are so strong the entire dock can be lifted 2' off the bottom by the ice at the outboard end and it will still stay bar straight. (60-foot long dock, too!)
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?