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Question DetailsAsked on 4/20/2017

Want to upgrade my 40G fish tank to a 60G fish tank 3'x3' on second floor. Will the floor hold?

Placement is on the second floor of a garage addition we added in 2009. It will be against the wall above a post that separates the two garage doors. They poured a new footing it seems as I can see the new concrete around that area between the garage doors. New tank will be 3'x3' and should hold 60G of water along with 60lbs of substrate, a stand, ~35-40lbs of rock and a smaller filtration tank that holds 20G of water.

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OK - 2x2x2' does equal 60 gallons, so right on 500# of water - plus 60# substrate, 40# rock, another 170# filtration tank water, and say maybe 100# total fish tank/base/filtration tank/filtration pump etc - unless this has a heavy base unit. So lets say 870# range as essentially a point load carried on one or maybe 2 floor joists, on a 4 square foot area = 220 psf bearing load roughly. Versus a design live load capacity of maybe 15-20 psf for older construction, or 20-40 psf for newer construction assuming the floor area over the garage was designed for living space (bed/bathroom/hall etc.).

While a lot of construction, especially if near a wall, can take 1000# or so of concentrated load - I would not count on it, and even if it can "bear" it, is likely to cause floor sagging over the long run because the "design dead load" is likely around 5-10 psf versus the 220 psf you are talking about - so even if the live load capacity could take the weight, over the long term I would expect (with normal construction) substantial sagging of the floor framing.

My recommendation - get a Structural Engineer (your Search the List category) to look at it and give you a remedial design - most likely a bearing surface at the floor (like a 2x4 bearing mat) to distribute the load over two joists, with possibly (depending on your flooring framing capacity) a corbel (supporting shoulder under the load area) or bross-beam section underneath the floor joists coming off an added post fastened to or adjacent to your garage door intermediate post (assuming the load is or can actually be right above the post) - so the new post would carry the weight of the tank and accessories down to the garage slab, and not interfere with your cars getting in and out. Might or might not need a new footing under the new post - for your design load quite likely not - might just be able to bear on the slab itself, depending on construction and how close it is to a construction joint.

And of course, consider how likely you are to upgrade in the future to an even larger tank like the person below did - would not cost very much at all relatively speaking (probably not over a hundred or two $ additional materials) to bump the new supporting capacity up a few fold in total weight capacity, assuming a new post is necessary, if that is a possibility.

It is possible you will not need new supporting post - just a larger supporting base for the tanks to spread the load over several floor joists - because your weight is in the range where, up against a supporting wall, the joists themselves may well be able to carry the extra load OK as long as it is not concentrated on one joist. A ton or so load you would almost definitely be looking at new supports, the three-four hundred pounds you have now is not much more than a couple of people standing close together so normal flooring can carry it though it might lead to long-term creep sag - so how much load spreading or additional support your planned load needs is highly dependent on the design capacity (and condition of the wood) or your current flooring.

One thing I would NOT do, to avoid undesireable beam sag and reduction of vehicle clearance, is carry the load to the garage door header beams - to the post OK if it has the capacity, but not to the beams themselves, because with the normal span even if they could carry the load you may get objectionable sagging which could reduce the overhead clearance for SUV's or pickups, which even if that does not impact you, could ruin a future sale to someone who does have a tall vehicle and needs every inch of clearance.

Here is another previous similar question with a lot more detail on the evaluation of whether it is safe or not, and wny a structural engineer would be a good idea before you risk a floor collapse. Granted your case is not as severe as the one below, but because you are over a garage door opening depending on how conservative that beam and post design wass, you certainly do not want to risk collapsing your garage door opening -

Answered 3 years ago by LCD


Sorry, the tank will be 2'x2'x2'

Answered 3 years ago by 8pixel


Thank you! Seems like I'm better off staying with my current 40G and not press my luck.

Answered 3 years ago by 8pixel

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