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I am adding a large fish tank (65 gallons) to my second floor and would like to make sure to distribute the load across as many joists as possible. Is my best way of doing that to build a long, short platform to set it on?

Here is the general idea, where dashed lines are the joists, solid black lines are the box (basically a structure of 2x4s screwed together with a piece of sheathing on top), and the orange is where the tank would go.

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If that sounds like the best way, then the next question is as to whether the positioning of the wood matters - i.e. using a 2x4, I can lay the base down by the 4 (making it easier to stabilize).

Update: This is close to the main bearing wall, however the old tenants moved the original wall in the basement (over by about 6-12 inches). This caused the house to shift a little and you can see that via a slant in the flooring. This is why I'm resistant to throwing that much weight in an idle configuration.

  • What is a "large" aquarium? 55g? 75g? 150g? What is "the box"? I'll leave the "long, short" thing alone for now. :) – isherwood Feb 16 '17 at 16:03
  • @isherwood Updated the question - more direct is 65g and the box is 2x4s screwed together with a piece of flooring on it – Justin Pihony Feb 16 '17 at 16:09
  • 65 gallons, let's see... a pint's a pound the world around... about 500 pounds, or a (small-ish) filled whirlpool tub. That's a substantial amount of weight. – Daniel Griscom Feb 16 '17 at 16:11
  • Plus a hundred pounds of gravel or more, plus the aquarium itself. I'd figure 800 lbs. – isherwood Feb 16 '17 at 16:14
  • I've kept a 55g unit at several locations in my previous 1950s home with no problems. How far from supporting foundation walls is the aquarium? – isherwood Feb 16 '17 at 16:15
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Any floor that is rated for humans and their furniture is more than capable of handling a 65 gal fish tank. Typical tank tables have only 4 legs, but even that means <=200 pounds per leg, which is on the order of a person standing on one foot. You have nothing to worry about. <-- unless your joists are way out of code.

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    Another way of thinking about this is a bathtub can hold anywhere from 30 to over 80 gallons when full (less when a person is in it but then there's the added occupant's weight) without any additional structural supports. – pdd Feb 16 '17 at 20:20
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    I'll buy that aside from the fact that it assumes modern construction built to code. I was holding out for more information. Anyone in the remodeling business has seen some scary shee-at at one point or another that causes second thoughts in cases like this. – isherwood Feb 16 '17 at 21:04
  • @pdd But a tub drains back to nothing in < 1 hour. This will sit there indefinitely...still think it's fine? Also, I made an update to provide more information about my concerns. – Justin Pihony Feb 18 '17 at 5:16
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The other top answer claims that if your floor can withstand a human, it can withstand a fish tank. That rule of thumb doesn't hold true in general because of the difference between live and static loads.

A person is a live load, meaning they move around and are not constantly weighing down on one point. Your tank is a static load, which means it will ALWAYS be bearing down on those joints. That's why it's fine to have 10 people (live load) in your room at one time, but a waterbed (static load) needs additional reinforcement.

That being said, my friend has a 50 gal sitting similar to how you propose to have your's, so it's probably okay.

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I have had many aquariums in many houses , mostly standard 55 gals , never a problem. Typically it is simple to use 10 lb/gal to estimate total weight; so 65 gal = about 650 pounds. I would be concerned about the slant in the floor you reported. You may want to consider a GFI in the closest electric receptacle.

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