I want to build a platform for a 400 gallon [about 3500lbs]. The platform will be 9x9ft. It will be 6′ above grade and freestanding.
The hot tub is 90″ square. The extra platform is to allow for maintenance access around the perimeter.
I used a programme at Lowes to design the platform. It suggests twelve [12] 6×6 posts. This is to cluttered for my liking.
How to design a support with Four posts? Or what is the minimum number of posts?
And how does this affect the dimensions of the other support members?
Thanks
Will
Edited 3/19/2005 10:03 am ET by will
Replies
I don't like the sounds of this, will. You say you're gonna have a hot tub elevated 6 feet off the ground on a free standing platform, then you want to know the MINIMUM number of posts you can use?
Think safety. That's a whole lotta weight to come down on some kid playing under that thing or the family sports car. I've built decks for maybe a dozen hot tubs over the years, but never one that high off the ground.
I'd encourage you to err on the side of caution, talk to a structural engineer.
Free speech leads to a free society.
Jim;
It seems like a very logical question to me. There has to be a minimum number of posts, preferrably four. The point is not to build anything inherently unsafe. I made the assumption that safety would be taken for granted. On the other hand I do not want to over engineer " just to be on the safe side" That is equally indefensible.
The point, after all is said and done I may have to consult an engineer. But in the meantime I thought I would throw the question into the forum in the hopes that someone with a structural background could give me solid ideas.
Thanks
Will
On the other hand I do not want to over engineer " just to be on the safe side" That is equally indefensible.
Perhaps you remember a news article about a year ago. There was a bar that had a second-floor deck attached to the outside of the building somehow. Best anyone could tell, it met the minimum standards. But when it was loaded with dancing carousers, it fell, and it killed a few of them.
I'll bet if we were to ask the bar owner about over-engineering versus meeting some minimum, his opinion might differ from yours.
So, are your willing to state that there will never be a party, and that no one will ever be dancing beside the tub, or using the deck for any other horseplay that will cause lateral stress?
And here's the real point. Talk to your insurance carrier. Find out what they will cover, and what they won't, as related to liabilities from this proposed deck. My guess is that they won't touch anything that is not inspected by local authorities, or designed by a structural engineer.
You're dealing with people's lives here. Take the time, and spend the bucks to do it right.
Unless you're the lead dog, the view just never changes.
Thanks for the response. The point is missed. It is not a question of over or under engineering. It is a question of appropriate guidelines for a safe environment. Nothing more or less.
Will
Platform seems a tad...I mean a LOT small. If you have a cover-caddy, how are you going to slide it off without falling off the side?
You could do the support with 4 posts, but you'd have to cross brace it, both directions....might look kinda funny.
Gotta hot tub out on a deck...lower the better, don't want to fall out drunk any farther than I have too.
400 gallons x 8lbs per= 3200 = hot tub== ok 3500lbs.
Now add .........lets say 4 people, maybe 5.
Thats another 700 to 1000lbs.
This is not the opportunity to under engineer something for any reason, especially esthetics.
Be safe and build it right. I would get professional help. Create a vision of building something substantial enough to park a good sized car ontop of.
Be safe........
Eric
I Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Thanks, But nothing was added to this discussion. The point is not OVER or UNDER engineering. See above post to Jim.
Thanks
Will
Thanks, But nothing was added to this discussion. The point is not OVER or UNDER engineering.
Nothing you wanted to hear anyway.
On the other hand I do not want to over engineer " just to be on the safe side" That is equally indefensible.
hhmmm.........
hey, have fun...........
Eric
Still waiting for my invite to the Darwin Awards.
I Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Edited 3/19/2005 4:37 pm ET by Eric Paulson
Don't sit down yet. This has potential
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I'm having deja vu.I Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Way back I bid on a project that had an 12' elavated spa. The Archy had speced out that the spa would be put on a reinforced block column, filled with sand.
wonder how that turned out ..
oh, there was a deck in the Plan too [:o)
That's pretty funny!
On the serious side though, well engineered!
What are you generating your drawings with?
EricI Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Hey Joe,Why dose kids in da sink ?
The person you offend today, may have been your best friend tomorrow It is easy to be friends with someone you always agree with.
First, I agree with the above, 9'x9' seems small - how will people access the hot tub"? Via diving board? I guess 9x9 could work if the platform had a railing around it and the hot tub was pushed into one corner... Here is another thing to think about... BTW we have a hot tub at our house... what about the cover for the thing? How will it be taken on and off, and where will it be (temporarily) stored while people are in the tub? They have those neat bars than kind of let you flip the top open like a convertible top - but you need to allow room for them. I wish I had; as it is only I can take the cover on/off - my wife can't manage it.
OK - now to your question. I'm gonna type as I think. 3500# tub + 1000# of people (adding a safety factor = 4500#. 9'x9' platform = 81 sq ft. OK, so that's 55.5# per sq. ft. Not really that bad. My gut feel is that nine 6x6 posts would be enough. Each of the 9 posts would need to sit on a concrete footer, some larger than others depending on the tributary load. The bottom of each footer would need to extend below the frost line. The posts would either need to be diagonally braced via x bracing, or they would need to be imbedded in the concrete about 18" meaning that each footer would need to be ~24" thick. That's a LOT of concrete!! This whole thing is really not sounding too feasible and rather expensive. Anyway, I'd go with 2x10 joists 12" O.C. and three double 2x12 girders (beams). 2x6 decking boards for extra rigidity.
The above will cause me to get flamed, and the flamers will say it needs to be engineered (because it does). If I'm lucky, someone may even call me irresponsible ;-)
Are you sure that something like the attached pic might not be better. This hot tub is sitting on a thickened edge slab with the decking built up around it...
Also, attached is a pic of the above layout I recommended - which is worth exactly what you paid for it... OK, so I didn't have much to do this afternoon... :-) but it will help you and others who take the time to take a close look at it to learn how to figure tributary loads.
Thanks:
I thought by referring to the structure on which the deck rests as a platform I might avoid the cofusion of it being a hot tub on a deck. The platform will abutt up to a deck at 8' elevation.[ the platform being 6' elevation] The extra allowance along the perimeter is strictly for maintenance should one need to get at the innards. The cover lifts away very easily as it is self raising. The reason we want it at the deck is for easy access in the dead of winter and to avoid stair climbing. The hot tub will be place eecentrically on the platform so that it not up against the wall of the house.{Again allowing access for maintenance]. Presently the hot tub is at ground level.
Thanks
will
will
over engineer
or not
it'll cost you
one way or another
minimum and decks don't belong in the same sentence
let alone hot tubs and decks
if you don't want to hear the responses don't ask the question
Hi;thanks for your response. We have probably exhausted this discussion. Many alternatives were suggested. most not very helpful for one reason or the . Obviously most soles are just as much at a loss about what engineering is required as I am. When I stated " minimum" it was not to be equated with " cheap" but rather aesthetics. But this point was lost. Further at no point did I imply that cost was a factor. As for building a wall and filling it with dirt...that is ludicrous. No aesthetic value at all. Also , I assumed that another possibility may be the use of steel supports. Nobody broached that as a possibility. Maybe it isnt? I will see a structural engineer about this. The only thing , that is not as easy way out in the country. If any interest I will post his recommendations.
Will
Try this calculator for a start.
http://www.awc.org/calculators/span/reversecalc/reversecalc.asp
Nice link... I am not sure how well it works though... I put in the below and it recommended 2x6 joists. Anyone with building expierence knows that is bogus... Or maybe I missed something?
Southern pine, 8'6" span, L360, 16"OC, 60# LL, 10# DL, wet=no, incised=no
Edited 3/20/2005 8:22 am ET by DIRISHINME
I checked the NC code which only went up to 40 live, 20 dead for other than sleeping areas. There are 4 choices for grade of southern pine. For #2 sp you can go 9'6" with a 2x6 on 16 centers. It looks like the first table may be ok but that sure does seem low. Like others have said "you build to code, you build to the minimum legal requirements".
http://www.amlegal.com/nxt/gateway.dll/NC%20Residential%20Code/part00382/chapter00657/section%20head00661/section00669.htm/subsection00670.htm?f=templates$fn=main-nf.htm$3.0#JD_TableR502.3.1(2)
I used to have a link to the Canadian Wood Council that had Span Calc 01 with US requirements but Phil must have had them take it out :-).
I looked all over last night and I could not find my links to some other tables that went up to 110 live. I used them for a deck that I built for a customer/friend a couple of years ago. He wanted provisions for a hot tub. I did about 1.5 times the max I could find in the tables. I used 6x6 posts for a 5' beam span with beam of 3 2x8's, 2x8 joists 16oc for the main part and 8"oc for hot tub area with 7' span and screwed 5/4 decking. Also used 10' joists to span the 7' so there was overlap on both sides of beam. I think overspeced but adequate would be an appropriate description. I do not think the extra material was all that much more than the amount for the minimum requirement.
Remember that thread a while back with a news story where a woman had put a swimming pool on a deck? What a hoot! Woulda been perfect for a darwin award except that she (thankfully) didn't die (nor did anyone else). Matt
I remember that one, duh. I firmly believe you could park a dumptruck on the one I described.
That article inspired me to start myself a folder in my pics for deck failures since the subject comes up just about twice a year.
The one being at graduation time when all the graduate revelers gather on decks to prove what liitle common sense they learned in school. The other being at some point during the winter when the loads come falling down from snow accumulations
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Found some other links, apologies to Phil and CWC guess they still love us, new calculator is avail.
http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
Southern Pine Council
http://www.southernpine.com/spantables.shtml
This is the appropriate one I believe:
http://www.southernpine.com/pdf/table16.pdf
For some reason when I went back it would not download the individual tables. I had downloaded the whole thing in Adobe and checked your example and it checks out at 8'6" for 60/10, 2x6 16oc.
Edited 3/20/2005 1:08 pm ET by RASCONC
The link I posted earlier, to the Western Wood Producers Assn, is a set of spreadsheets that let you enter any live & dead load (including snow weight if for roof), select species and grade, set spans, indicate whether the wood is incised for PT, etc. It calculates shear, bending, and deflection and tells you if any of them exceed allowable limits. Takes some time to understand - it's defintely harder than reading span tables. There is also a spreadsheet for posts & studs - I don't understand that one yet - LOL.
Kinda like an engineer in a box. (Wish the engineer on this project behaved this well - LOL!) Of course, if all you can get is SYP it won't do you a lot of good...
Did you post that in this thread? I could not find it.
Edited 3/20/2005 1:53 pm ET by RASCONC
No he started another thread.In fact I thought that my computer screwed up and presented it to we as unread untill I started reading it and see that it is a differeent version.a shearch on hot tub should show it.
Thanks
I didn't intentionally start another thread - I think Prospero did it for me. I even got a response on the post - from this thread - and now it's gone elswhere. ??? Thanks for finding it - I thought I was losing it!
The CMUs and infill was not intended as luduicrous and it can be made as aesthetic as you want to. It was suggested as a viable solution to solve your problem. Dont bother to post a Q and demean good solutions. If there was anything laughable in the thread, it was the Lowes solution you brought forward first, which you obviously recognized as silly.but since you reject eh CMU base, I will tell you that it can be done with six posts, the right beams, and 2x10 joists. I won't bother to add details for fear that you will find it ludicrous. Go ahead and get hurt or not as the water gods dictate
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Yea, OK, let us know what the PE recommends. Matt
"We have probably exhausted this discussion."
Not at all - I think it's just beginning to take on a life all it's own. (-:
Actually, you've gotten more useful advice than you realize. (I think)
Someone mentioned cross bracing. That's definitely a good point, and you may not have thought about it.
Steel is also an option, as you mentioned.
I don't see any reason why it couldn't be done safely with 4 posts. But as someone else pointed out, you'll definitely need footings. Add in some pretty large beams, a deep floor system, and some cross braces, and I don't think it's possible to have quite as much of an "open" look as you want. (Assuming wood framing)
With steel, you might be able to get shallower beams and some moment connections that would give you the open look. But I don't know a great deal about steel design, so I can't give you any more specific advice.
Looking at your profile, I'd say you've been hanging around long enough to know that folks here tend to get testy when they think someone is trying to do something dangerous and/or cheap. When you used the word "minimum" that's what came across.
So don't take it personal. Some threads just take on a life of their own. There's no rhyme or reason to it.
We could never learn to be brave and patient, if there were only joy in the world. [Helen Keller]
Thanks Boss Hog:
You are quite correct in your assumption that I would like an uncluttered area under the deck. Not to store anything as some have suggested. Only to preserve the aesthetics if at all possible. Even though I plan to landscape with shrubs and flowers, the underside of decks with unusable space always look unappealing.
Also I did fax my request and plans to an engineer this am. If any interest I can let you know what ideas he has.
I also did like the suggestion and photos offered by Pro-Deck.
Thanks,
Will
Pro-Dek is one of the best there is. He's been there and done that - and lived to tell the tales.Basically, you desire a simple/ elegant solution, for a problem that has many issues, esp regarding safety. Arriving at simple and elegant solutions is one of the most difficult aspects of our business and what separates the great from the good.All too often, clients come to us asking for a solution to near impossible problem and treat it as though it's beer time talk. UGH! But you continued and stated that your motivation stemmed from the initial proposal/ design being "too cluttered for my liking." This is disrespectful to the project at hand and of our abilities. Hence the replys you got.Acknowledging issues you feel important for us to address and informing us of the context within which the hot tub will exist and why you want such a free-span and limited posts/ columns will focus the discussion to give you a more helpful result. If you don't know what is important, ask why this design was determined. We all like discussing this, pros, cons, I remember whens, told you sos, and news clippings, but without adequate info in the initial post, all you will get is inadequate results.Basically, what you really need is an engineer. Be sure to have your desired effect defined.F
Due to regional differences, we would not be able to build a deck like ProDek's and pass inspection unless it had an engineer's stamp on the plan, and it was all detailed pretty well. Reasons? 1) 6x6s are not normally used as joists, and our span tables don't cover their use for that application. 2) we can't lag bolt and/or nail diagonal bracing - it has to be through bolted (as is the case with ledgers attached to a house). Still, it looks pretty sturdy to me...
Re the lumber commonly used, I think it may be due to the fact that out west large timber is more readily available. Elsewhere, for example, I've seen reference to them using solid timber for headers over windows, doors, etc, as opposed to built up headers. (sandwiched 2bys) Solid headers are unheard of here in the SE, except maybe in the very rare occasion of a timber framed house. This does not explain the difference in bolting requirements though. As a general rule of thumb, we can't use lag bolts for anything structural, unless their exact usage was specified by an engineer.
I do see one common theme in this thread though... In the original posting, the guy said that the deck design software at Lowes prescribed 12 posts. Not one person here has thought anything like that was necessary - just shows that the Lowes "automatic design software" really gave the guy his money's worth ;-)... Or maybe Lowes is just trying to sell more lumber. Matt
You guys have put an awful lot of thought towards this question, but none of it was helpful - the point is still missed. A big plastic spa can only look as nice as the framing that supports it, and all of this complicated engineering will play havoc with the under deck aesthetics. The solution is obvious. Think: landscaping. A few well placed shrubs and a little time are all that is needed here - I'm not a gardener, but I would think that three or four fast growing giant redwoods would do the trick. Give them lots of water, and keep them pruned at four feet. You can even use the cuttings to finish the deck while you wait. Problem solved (or is that too "simple" for you guys?) Saul
landscaping is an assumption in my book, but the owner never asked a thing about that. You have to hold it up before you can make it look pretty.And maybe you don't realize it, but roots can do serious damage to support structures and foundations.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffen, thank you for the mercifully patient response. Of course you're right, and I just finished apologizing to DIRISHINME for this - my suggestion was supposed to sound stupid, I just didn't realize how convincing I could be. I hope it's not too late to say thank you to all of the posters in this thread who patiently persisted to explore an important subject like this. I was learning a lot; I guess I just wanted to keep it going. All kidding aside, I know someone who was disabled when a deck collapsed, and I don't think enough could ever be said on the subject of safe building practices... I suppose I should have just said that in the first place. Thanks.
I wonder what was the cause of the deck collapse in which your friend was hurt?
Matt
The deck was off of a second story, and wasn't properly attatched at the ledger. It was overloaded during a party - I heard it only had ten people on it, but the worst injuries were from people below.
I've started wrapping a ZMAX metal strap around the back of my ledger boards on every 4th joist, nailing to the top and bottom of the joist. It prevents the deck joists from pulling away from the ledger board.I can't imagine the guilt of hearing that a deck I built collapsed, injuring or killing someone. Not on my watch... I overbuild. Of course, most of us do who wander through here. It's little wonder Will got the reception he did by asking about the minimum posts needed for a hot tub platform. Serious weight needs serious structural framing.
To Mac and all the others that tried to help:
I changed my mind. Instead I am building an enclosed hot tub .Not over-engineered as many of you suggested. Plans approved by the engineer. Concept stolen from a grade school dropout in the hollers of Kentucky. Accommodates two families.
Could not ask for more.
Will
Hilarious!If you get a big enough tub, it could double as a water supply tank for the locals!<!---->View Image<!---->
It was because lowes automatically asumes a 2x6 joist and cannot be reset for normalluy sized joists. I wouldn't build a deck larger than five or six feet with 2x6s
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Me to.
Matt
Given this new information, I would just pour a footing and lay up block. Cheaper and better.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
That was way nice of you to do that for Will.
May I ask, what did you use to generate that drawing?
And the wise guy in me can't help but comment..............
The hot tub in the photo............thats gotta be a real serene place to hang out and unwind, especially when the furnace kicks on!! Oh well, I know it wasn't there by design.
EricI Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
I'm using SketchUp !
1) M/S Visio - good for quick and dirty.
2) not sure what you mean about the furnace - it's around the other side of the house. Maybe you are looking a the exhaust for the downdraft cooktop...
Matt
Thanks,
yeah, just to the left of the hot tub. Looked like a direct /power vent furnace vent!
EricI Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
OH - that is the electrical box/disconnect for the hot tub - I forget - has to be not closter than 5' but not further than 10' - or something like that.
Matt
The poster who jokingly (I think) showed the hot tub on a concrete foundation may have actually hit on something: You could build a square support platform of four walls of concrete block (on the required footing at the proper distance below grade to be below frost line), reinforcing the corners with re-bar and grout in the cores (and maybe in the center of each of the four walls), filling that with sand and pouring a concrete lid. Then build your deck around that so the deck is two feet higher. This should all be engineered to be safe, and I don't know that it would be any cheaper than a wooden platform, though it seems like it would certainly be sturdy!
This is just my getting crazy, but you might even be able to set a concrete culvert on end on a footing below frost and build a square "lid" on it for the tub and surround that with the wood deck at 8'.
It wasn't a joke Danno, that's what the Archy specified. That's one sure way to be safe hey ?
Yeah, if the thing weren't filled with sand it'd make one heck of a bomb/tornado shelter! ;-)
PS: to answer your question directly about 4 posts, there is no way in heck 4 posts would support it. Even for a regular deck (no hot tub) in order to span 9'. a girder would need to be a double 2x12s. MAYBE a 4 post hottub deck with 8x8 posts, 24"x24" footers, quad 2x12 girders and 2x12 joists on 8" centers...
I think Pif and others have the right idea (masonry all the way). 9x9x6' tall: (assuming a minimum depth frost line):
Still nothing to do but waste time...
Edited 3/20/2005 8:08 am ET by DIRISHINME
Here is a picture of one I built some time ago. I like using treated 6x6. Kind of looks like a railroad trestle................
"Rather be a hammer than a nail"
Bob
That's more like it!
I must ask though...........I see you have it braced in one direction with 6x6 bolted and in the other direction with 2x nailed , screwed??
What gives. Not meaning to be testy or offensive, just asking.
EricI Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Just the way it all worked out Eric............10- 8' 6x6's the 2x6's were nailed and later lagged with 2- 3/8x4" galvanized lag bolts and washers top and bottom of each diagonal brace. The 6x6 diagonal braces were first nailed then bolted top and bottom with 3/8x6" galvanized lag bolts and washers.
If I had pulled the 6x6 cross in to match the post and diagonal brace I would not have the 8' needed for the outside edge of the tub. Most tub surrounds need to be supported all the way around the perimeter. Some are made so you can cantilever them about 6".
"Rather be a hammer than a nail"
Bob
Minimum number of posts, 'eh ?
You will need one post.
9'x9'x6'
There you go. Done.
And it isn't even overengineered.
The person you offend today, may have been your best friend tomorrow
It is easy to be friends with someone you always agree with.
Luka,
I just read this and I LAUGHED TILL MY SIDES HURT! Thank you.Dave
Should have include Luka's posting...
Should have included Luka's post in my comment
Minimum number of posts, 'eh ?
You will need one post.
9'x9'x6'
There you go. Done.
And it isn't even overengineered.
Dear Mad Dog:
I certainly do not appreciate your comment.
As stated 3 or 4 posts prior I have already submitted the proposal to an engineer. In initially posting the question it was my hope the someone had confronted the problem before and would have insight into the issue. There have been some good ideas. There have been suggestions, that if one had read my initial post, that were off the wall. Like, why not place it at ground level. Now if that was what I wanted I would not have asked for help. Then there were those that bordered on the innane.
I am not a builder by trade....but I built my own home and have a lot of knowledge gained by reading. As the guy at the kitchen cabinet shop said to me: " do not forget to install th e cabinets with the doors facing the room. " He carried on to say " you do not know how many installers I have to remind of that"
On the other hand I was hoping to have an engineer that may peruse these fora give some finite suggestions.
Anyway
Thanks
Will
That's fair enough. I just reacted to your tone to several of your replies, where it seemed condescending, and I'm sorry to have misunderstood you. I have a meter built in for that, and it was redlining.Prior post respectfully withdrawn. Good luck with the engineering.
OK - I didn't get that it was a joke. Next time maybe add a smiley face? Sorry.