Floor support for 600 gallon water tank

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Cahoffa, Jun 23, 2020.

  1. Cahoffa

    Cahoffa New Member

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    I'm installing a 600 gallon water tank on an inside floor. How can I be sure that the floor is strong enough to hold 5000 lbs? There is a main beam running down the length of the floor. Half inch plywood rests on top of that and extends to each foundation wall. An array of 2 x 6 rests on top of that finished off with 3/4 plywood (see the pictures). One other interesting find is a shorter beam (about 6' long) that runs parallel to the main beam but not the whole length of the room. The water tank would sit between this smaller beam and the wall. The whole room is about 10 feet wide by 12 feet long. I suppose if the tank does break through the floor, it won't fall very far!
    Thanks! IMG_6518.jpg IMG_6518.jpg IMG_6514 copy.jpg Floor cross view .JPG
     
  2. Jeff H Young

    Jeff H Young In the Trades

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    looks pretty sketchy but I say go for it! Your insured right?
     
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  4. James Henry

    James Henry In the Trades

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    You better find someone who knows what they're doing.
     
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  5. Sylvan

    Sylvan Still learning

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    Actual weight is 4998 PLUS the tank I would have a carpenter of structual engineer make the call
     
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  6. Jeff H Young

    Jeff H Young In the Trades

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    the guy at home depot will know
     
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  7. fitter30

    fitter30 Active Member

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    What is the foot print of the tank this has to known how the weight is spread out.
     
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  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Residential home design usually can handle 50#/sqft, usually in a 40:10 live:dead load ratio. That 10# is for the subflooring and finished floor, plus maybe a non-load bearing wall. Start to throw in a significant point load, and the normal load calculations no longer are valid.

    I think that I'd want to install some support underneath the floor with some pylons and beam to prevent floor deflection. But, this is why you may want to call a structural engineer to calculate what's needed so you don't go overkill or end up with the floor sagging and giving you problems.
     
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  9. Cahoffa

    Cahoffa New Member

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    The tank is 58" long by 35". It has to be tall and narrow to fit through the door.
     
  10. Cahoffa

    Cahoffa New Member

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    Great! Thank you for the information. We have contacted a contractor.
     
  11. Jeff H Young

    Jeff H Young In the Trades

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    Good luck!
     
  12. WorthFlorida

    WorthFlorida The wife is still training me.

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    The most important part is the footing. All the beams no matter what size and the amount won't mean much if the foundation can't handle the load. A pile of bricks, wood and plywood may not cut it.
     
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  13. Jeff H Young

    Jeff H Young In the Trades

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    hmm you mean rotted wood laying in the dirt might not be a good thing?
     
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  14. wwhitney

    wwhitney Active Member

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    Here's a simple answer: it's not.

    Your existing beam supports are less than adequate (to put it politely). Leaving aside the issue of beam and joist sizing, each beam support should have a proper post and a footing sized based on the tributary area, the 50 psf total floor load jadnashua mentioned, and the soil bearing capacity. The soil bearing capacity depends on the soil type, but in the absence of a soils report is often taken as 1500 psf as a reasonable minimum (at least in much of the US, soil types could be different where you are.)

    For example, consider a single story building that is 20 feet wide with continuous foundation walls on the perimeter, and a girder down the middle supporting 20' floor joists only (no ceiling or roof load). Then the girder tributary width is 10' (the middle 10' of the 20' span). So if the girder has posts every 5', each post carries 5' x 10' x 50 psf = 2500 lbs. With a 1500 psf bearing capacity, that post should have a footing of at least 1.66 square feet. [And where issues of frost do not require a greater depth, should be at least 12" deep bearing on undisturbed soil.]

    Of course, that just covers the usual loads, the tank requires its own supports. You mentioned that the footprint is 35" x 58". At a minimum you'd want a properly sized beam 58" long centered on the footprint, with two properly sized posts and two footings. Since the tank weight is 5000 lbs, if the 1500 psf minimum soil capacity is applicable to your area, each footing would need to be at least 1.66 square feet.

    Cheers, Wayne
     
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  15. Sylvan

    Sylvan Still learning

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    The International Residential Code, on which most local building codes are based, requires that floors in non-sleeping rooms must support a minimum live load of 40 pounds per square foot, and floors in sleeping rooms must be able to handle a live load of 30 pounds per square foot
     
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  16. Jeff H Young

    Jeff H Young In the Trades

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    In that case Id say she is good to go just fill the tank real slow and see what happens an extra 5 or 6 thousand pounds wont hurt the place looks over built any way with that beam laying on dirt
     
  17. Cahoffa

    Cahoffa New Member

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    Thanks, Wayne. I didn't build the place, so I don't take offence. In fact, I would love to tear the arctic entrance down and rebuild it using a concrete foundation, but a lot of people use wood foundations here in the Yukon. I appreciate all the information, I find it all very interesting. We might just build an outdoor structure to house a 1000 gallon tank. Putting the tank inside was the preferred option because of potential freezing issues with possible -45 degrees Celsius days here in January.
     
  18. Cahoffa

    Cahoffa New Member

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    Unfortunately, we don't have a Home Depot here in the Yukon.
     
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  19. Jeff H Young

    Jeff H Young In the Trades

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    Excuse me I was poking fun... This is a complex job a couple of pictures and asking a plumber ( or just any random person on internet) about putting 5 or 6 000 pounds on your house floor is like asking a 5th grader about brain surgery. Amazingly these guys are taking it serious. So like I said go for it see what happens
     
  20. Cahoffa

    Cahoffa New Member

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    Ha, ha! I thought you were serious, too. My hope in starting this discussion was to pick people's brains on the problem, and the pictures help to explain the situation. I am appreciative of all the structural information that I received from various members on this forum.
     
  21. wwhitney

    wwhitney Active Member

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    So, maybe I'm misinterpreting the pictures, but I took the blocks stacked between the wood beams and the earth to be stone (often with a layer of wood shims directly under the beams). If you have wood cribbing directly on the earth, that's not good.

    Proper footings don't have to be concrete, they could be gravel pads. A proper (pressure-treated) wood foundation will use gravel footings to provide drainage under the wood.

    Cheers, Wayne
     
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