Need some info on Deck Load Capacity

[Sarge]

I looked around on the web but could not get good clear information so here I am asking my Benos Brothers for help again.

I am having a hot tub installed next month. I am building a platform for it to sit on. It is about two feet off the ground so too high to use concrete. I am building it as a deck and need some info on beams, joists, etc.

If you can help, please shoot me a PM and I'll be more specific.

Thanks in advance

Kevin

[Chris Keen]

Kevin, I'm no engineer, but I do know 1 thing ...... water weighs 8 pounds per gallon. So factor that into the weight of the hot tub, and don't forget the weight of the person(s) using the hot tub as well. It will definately need to be very sturdy.

[Flexmoney]

Yeah...might be best to leave the water out. Kinda like lifting weights (it would be a lot easier if they weren't so heavy).

Seriously...you may have local building codes that spell that out? Your hot tub salesman might be able to point you toward that info.

Also, note that Conrad works at a place that makes those metal hangers and ties that are used in such applications. Careful though...he doesn't even know his bullet weight sometimes.

I wonder if "up in the air" means you also lose more heat energy ?

[Sarge]

Chris, I already know the tub weighs 5000+ lbs. when full of water.

Kyle, My local building department approved a plan that I know is way too weak so they are not much help.

The tub sales guy said "just over build". So not much help either.

The only thing I have been able to gather from the web and a few other sources is to shoot for a live load of 100 PSF. I am trying to verify if that is accurate info and if my beam dimensions, joist dimensions and spacing, etc are in that range.

I work in a town that has a building inspector as well but all he would tell me is, "sounds like you will be fine".

I think I am fine also but I just would like to verify it.

FYI- 2X10 beams sandwiched onto 4X4 posts cemented to 30" deep in 18" wide holes. Max span of beams right around 6 feet.

2X10 Joists 12" on center. Max span between beams around 4 feet.

2X6 decking on top of that.

Home depot did a plan for me that used 2X6's where I used 2X10's and they claimed a live load of 80 lbs PSF.

So, like I said, I think I am good to go.

[GrumpyOne]

Sarge, I have a 5 person hot tub on a deck. I have no idea how much weight my deck will hold, but it will hold probably 5 times what the tub weighs with water. My deck is 14' x 14', I started out with 9 holes, 18" x 18" square, 24' deep, with 6" on sacrete in the bottom (to keep the post from sinking), 9 - 6" x 6" pressure treated posts resting on top of the sacrete, 2" x 8" pressure treated joists on 12" centers, except for the middle of the deck, where I put the joists on both sides of the center 6" x 6" post, topped it off with 2" x 6" pressure treated pine. I believe I could park a semi on top of it and it would be ok. It doesn't shake, move, nothing. I have a deck on either side of it, not built quite the same (but I knew there wasn't a tub going on them) that has the joist on 24" centers, all pressure treated, 2" x 6" pressure treated pine as deck boards. They move (shake/vibrate) just the tiniest bit under heavy traffic. Whatever you put down, stay away from what they call 5/4 deck boards with the rounded edges. They will warp badly, and flex quite alot. Use 2" x 6" pressure treated for all the deck boards, they are ususally only a few cents more per board than the 5/4 stuff anyway, and much thicker.

Edit to add: my tub is 450 gallons ( I think...it's been a while since I looked. Hell, it could be 550 gallons!), plus the weight of the tub, so it's probably a bit over 4,200lbs. I would definitely go with 6" x 6" post though. I have one deck, 30" off the ground, on 4" x 4" post that will sway a bit when there are 9-10 people on it. I also completely over build every thing.

Edit #2: I would also NOT pour concrete around the post, but set the post on concrete. Use tamped sand or small pea gravel around the post to promote wicking away of excess moisture. Concrete around the post will eventually rot the post, even pressure treated, as it (the concrete) will leach out the pressure treating salts, and it will weaken the concrete (from the salts). Most of the pressure treating is done with a copper/sulfate mixture, which is a salt.

PS. In a former life, I was a concrete/brick/block mason.

Edited July 19, 2010 by GrumpyOne

[NoSteel]

I will assume that since you are in Ohio winter snow load will also be a factor. If not covered over head, you will need to be sure this is considered in the calculations. Another thing to consider will be footing requirments. Not sure if frost is a big issue where you are located but waking up in the morning to find your heavily laden deck pitched to one side might make for a bad day. Again, no engineer but know you need to add these question to your list....

[Sarge]

Sarge, I have a 5 person hot tub on a deck. I have no idea how much weight my deck will hold, but it will hold probably 5 times what the tub weighs with water. My deck is 14' x 14', I started out with 9 holes, 18" x 18" square, 24' deep, with 6" on sacrete in the bottom (to keep the post from sinking), 9 - 6" x 6" pressure treated posts resting on top of the sacrete, 2" x 8" pressure treated joists on 12" centers, except for the middle of the deck, where I put the joists on both sides of the center 6" x 6" post, topped it off with 2" x 6" pressure treated pine. I believe I could park a semi on top of it and it would be ok. It doesn't shake, move, nothing. I have a deck on either side of it, not built quite the same (but I knew there wasn't a tub going on them) that has the joist on 24" centers, all pressure treated, 2" x 6" pressure treated pine as deck boards. They move (shake/vibrate) just the tiniest bit under heavy traffic. Whatever you put down, stay away from what they call 5/4 deck boards with the rounded edges. They will warp badly, and flex quite alot. Use 2" x 6" pressure treated for all the deck boards, they are ususally only a few cents more per board than the 5/4 stuff anyway, and much thicker.

Edit to add: my tub is 450 gallons ( I think...it's been a while since I looked. Hell, it could be 550 gallons!), plus the weight of the tub, so it's probably a bit over 4,200lbs. I would definitely go with 6" x 6" post though. I have one deck, 30" off the ground, on 4" x 4" post that will sway a bit when there are 9-10 people on it. I also completely over build every thing.

Edit #2: I would also NOT pour concrete around the post, but set the post on concrete. Use tamped sand or small pea gravel around the post to promote wicking away of excess moisture. Concrete around the post will eventually rot the post, even pressure treated, as it (the concrete) will leach out the pressure treating salts, and it will weaken the concrete (from the salts). Most of the pressure treating is done with a copper/sulfate mixture, which is a salt.

PS. In a former life, I was a concrete/brick/block mason.

Grumpy- I am an avid over builder as well! It is always nice to meet another .

I have always set posts in concrete. Oh well, they will last my lifetime.

I have always used 4X4's with success. I just put more in than the plan calls for. My actual deck is about 4 ft off the ground and is as solid as a concrete slab. Last year we put a kiddy pool on the deck and filled it with water. Turns out it had 750 gallons of water in it. It was up for about 2 months with no ill effects.

No Steel- 30" is the minimum around here to get below the frost line.

Thanks guys.

[GrumpyOne]

Sarge, I have a 5 person hot tub on a deck. I have no idea how much weight my deck will hold, but it will hold probably 5 times what the tub weighs with water. My deck is 14' x 14', I started out with 9 holes, 18" x 18" square, 24' deep, with 6" on sacrete in the bottom (to keep the post from sinking), 9 - 6" x 6" pressure treated posts resting on top of the sacrete, 2" x 8" pressure treated joists on 12" centers, except for the middle of the deck, where I put the joists on both sides of the center 6" x 6" post, topped it off with 2" x 6" pressure treated pine. I believe I could park a semi on top of it and it would be ok. It doesn't shake, move, nothing. I have a deck on either side of it, not built quite the same (but I knew there wasn't a tub going on them) that has the joist on 24" centers, all pressure treated, 2" x 6" pressure treated pine as deck boards. They move (shake/vibrate) just the tiniest bit under heavy traffic. Whatever you put down, stay away from what they call 5/4 deck boards with the rounded edges. They will warp badly, and flex quite alot. Use 2" x 6" pressure treated for all the deck boards, they are ususally only a few cents more per board than the 5/4 stuff anyway, and much thicker.

Edit to add: my tub is 450 gallons ( I think...it's been a while since I looked. Hell, it could be 550 gallons!), plus the weight of the tub, so it's probably a bit over 4,200lbs. I would definitely go with 6" x 6" post though. I have one deck, 30" off the ground, on 4" x 4" post that will sway a bit when there are 9-10 people on it. I also completely over build every thing.

Edit #2: I would also NOT pour concrete around the post, but set the post on concrete. Use tamped sand or small pea gravel around the post to promote wicking away of excess moisture. Concrete around the post will eventually rot the post, even pressure treated, as it (the concrete) will leach out the pressure treating salts, and it will weaken the concrete (from the salts). Most of the pressure treating is done with a copper/sulfate mixture, which is a salt.

PS. In a former life, I was a concrete/brick/block mason.

Grumpy- I am an avid over builder as well! It is always nice to meet another .

I have always set posts in concrete. Oh well, they will last my lifetime.

I have always used 4X4's with success. I just put more in than the plan calls for. My actual deck is about 4 ft off the ground and is as solid as a concrete slab. Last year we put a kiddy pool on the deck and filled it with water. Turns out it had 750 gallons of water in it. It was up for about 2 months with no ill effects.

No Steel- 30" is the minimum around here to get below the frost line.

Thanks guys.

Yeah, they won't last my lifetime though....I'm gonna live to be 200! Really though, I think setting the post on the concrete is a better solution (It was in my case anyway, as my ground is a bit swampy-I live in a wetlands swamp!), as I have set post in concrete as well before, but the post sank under the weight. But the size of the hole you are talking about, I don't think that is gonna happen. Isn't it strange how us 550 loaders think alike?

[GrumpyOne]

For you, Sarge. Here's a video about decks.

http://www.youtube.com/watch?v=QQ7Ue5emo6I

[Ed Deegan]

not an arch or an engr. But as someone who is in the GC business, try a flat 6" pad and then add 8" block. Welded wire mesh would be fine as reinforcement in the slab. Make sure you put some L shaped rebar in the slab to go up through the blocks (ties it together structurally). Block will support the tub and if you want to fill the block area with compacted earth or stone, you can do that as well. That will hold fine. The tub wont be supported by the deck and you could build your deck around it.

Costs for such a structure (depends on your labor ability) would be about $8-10 a foot for the slab, and 7.50 a face foot for the block/mortar/mixer etc. Assume $25.00 a ton gravel/stone. If your tub is 8 x 8 and you want it 2 feet off the ground, stone is less than 300 for the job. A contractor will charge for the whole job, around 2k.

You want to make the slab a little bigger than the tub. i.e., 8 x 8 tub, 10 x 10 slab will work just fine.

Make the slab 10 x 10 = 100 SF @ $14.00 a foot commercially for something that small. If you do it yourself, rent a mixer and get 2.5 pallets of redimix. Redimix at home depot is about 185 a pallet, rental mixer for a saturday 150, $200 bucks for your forming materials, WWM and rebar and $50 bucks worth of beer for your buddies.

Block would be 64 SF @ $14/15 a square foot commercially for this size job. If you are 2' high, thats 3 courses of block. If you dont know how to use string lines, just use a level. If you keep your slab level, it will help with this part. The top of the block needs to stay level.

Gravel would be about 10-11 tons.

The project is small enough, you may run into higher unit costs just to make minimum quantities (concrete/block/gravel).

[Sarge]

For you, Sarge. Here's a video about decks.

http://www.youtube.com/watch?v=QQ7Ue5emo6I

Had a feeling it would have nothing to do with building a deck!