# [Wet Thumb Forum]-Reinforcing wood floor for Tank



## imported_chrismisc (Jul 25, 2004)

Hi All,

You might be thinking "wood floor + fish tank = disaster." I guarantee that's what my husband is thinking. Long story short, we are in the midst of purchasing a house that meets most all the criteria except a nice slab floor for my 38 gallon tank. I had a tank bust a seam and dump about 25-30 gallons in our old house--fortunately there was a crawlspace so the water didn't pool so much as drip through, and in spite of it's being a fast leak, there was little damage.

But, what about the weight factor? I know 1 gallon weighs 8 lbs, plus tank, gravel, rockwork, stand, and hardware. That's got to be around 10 lbs per gallon gross weight, at least, right? So I'm looking at 380 lbs. That might be alright, but it's not the newest house, and some day I want to get a bigger (125 gallon?) tank. So finally, my question is whether there's a pracitcal limit to the amount of weight an oak wood floor with diagonally running joists can support. Does anyone know of any rules of thumb? What about reinforcing the floor from below-- would that just be a long Saturday and trip to the hardware store, or are we talking invasive surgery? All you structural engineers, please advise-- or at worst share your leaky tank stories! Thanks.

Ooh, also (did I say long story short?), what is the preferred method for leveling a tank on a not so level tile floor? In the past, I've used shims from work made of a synthetic stuff kinda like MDF but much harder, plus a level, but htis time the tiles are really irregular, and I'm not keen on the restaurant table with all the napkins stuffed under one leg so it won't wobble-kind of thing.


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## imported_timlawyer (Jul 14, 2003)

If your floor is strong enough for 4 or 5 people to stand around and talk - you should be just fine.
Regarding floor tile and wood floor surfaces, you should be more concerned with pounds per square inch in addition to overall weight. An aquarium which weighs 500 pounds (such as 55gal) has 576 square inches of area on the bottom - which translates to just over 1 pound/sq inch - this is much less concentrated force than a normal adult wearing shoes. This is something to keep in mind when leveling the aquarium. Using shims or other "legs" will have the effect of putting a large percentage of the whole weight on one small area - be careful about this.


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## Oodi (Sep 21, 2005)

Interesting. How do you level a stand on a substantially uneven and unlevel floor? Place the stand on a slap of styrofoam?


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## imported_buz2au (Aug 8, 2005)

Timlawyer’s statement is not quite right, the mass of the tank will be 1000lbs for 125gal and would be transferred into the frame of the stand, the critical bit is the contact the frame has with the floor. If the frame has say 4 legs which are the only contact with the floor then you would have 4 point loads on the floor of 250lbs each, on the other hand if you had perimeter frame say 2” wide and the tank was say 6’x11/2’ wide would give you a uniform load 2.8lbs/sq inch over the perimeter footprint, how the floor is loaded can make a big difference.

As for reinforcing the floor, it depends on a few things like what the floorboards, joist and bearers are and their spacings and spans, if just the floorboards need reinforcing then a nog between the joists is all that maybe required, maybe extra joists or some of the existing joists to be doubled up, or even extra supports for the bearers or stiffing of the existing bearer maybe required, but that would best be left up to a engineers or building designers decision.

buz2au


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## imported_russell (Sep 14, 2004)

buz2au, isn't it also true that there is more weight distributed to the corners of the frame of the stand? that is what i was told, but i'm not sure if it's correct.


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## imported_buz2au (Aug 8, 2005)

Hi Russell, its all to do with resulting forces in compression & tension, like in a truss, where say the timber used is 90x45mm pine spaning 10 metres can carry a 1000kg of concrete roof tiles, or you could use a 330x65 laminated beams as a rafter (I did check that on my timber tables by the way). Now a truss is supported at each end only & allowances are made for the bottom cord of the truss to move, with a wall the bottom cord or bottom plate is in contact with the floor so it can't move therefore the force in it is transferred to the floor, some force will make it to the corner but very minimal, (uniform distributed load rule). If the frame is not in contact with floor & is built between 4 corner legs then the total load will be equally distributed to all legs ie ¼ of load to each leg, then the load is transferred to the floor via the leg foot print, giving 4 point loads (point load rule). All this physic theory was a long time ago so don’t ask me to do the maths, these days I just punch the numbers in program & let the computer work it out for me, ain’t life easy LOL.


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## JERP (Feb 4, 2003)

Minor threadjack, but most fish tanks support the weight by the sides of the tank. The bottom of the tank does not touch the stand or is load bearing. This is why stands can be open on the bottom and support the only outer edges of the tank.

back to subject...
I wouldn't worry about the wieght of the tank in a house. If your floor won't support the weight of a 400lb tank, it won't support the weight of two fat Americans in a love seat.

For the uneven tile floor, you might try dense foam rubber pads on the bottom of the stand legs. It's not a level surface that a tank requires, but a flat one. You can have a bit of "tilt" as long as the surface of the stand doesn't curve. The most labor intensive solution is to re-set the tiles under the legs of the stand so it's level. Re-seating the tile should only be necessary if your tile job is truly horrible.


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## imported_buz2au (Aug 8, 2005)

It’s not how the tank is supported on the stand, but the transfer of the load from the stand to the floor that is the problem.

The uniform load transfer to the floor is the area of contact of the bottom cord of the trusses and the floor.

The problem is not that the floor is strong enough to carry the load, it’s the stiffness of the floor structure, deflection in floors maybe up to 10-12mm over large open spans (Dead Load Deflection = span/300, Live Load Deflection span/360 and have some bounce (Dynamic Load 1.5mm at mid span)to them.

Packing the base or legs of the stand with compress fibre cement sheeting (fribo) would also be a better option as it would be more stable and will not compress over time.

With all the above we are talking about modern light frame timber construction, older (25 years or more) type homes, both here in Australia and USA, were over designed by a mile, and construction techniques were a lot different and stronger.


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## imported_chrismisc (Jul 25, 2004)

Thanks everyone for all the input! I didn't end up putting the tank on the tile floor, thank goodness. It's saltillo tile, and if you aren't familiar, it's handmade in Mexico, air-dried out doors (hence, little critter footprints are often a feature), and thus pretty irregular in thickness--we're talking a half inch at times. I was thinking I'd have to carve a piece of some industrial, high density foam to ~level & set the tank on that to absorb the unevenness somewhat.

The tank's still on a second story wood floor (and it's a 50 gallon Tall now, too), but it thankfully is pretty darn level now. Actually, cool bit of news: The tank's against a load-bearing wall, and was a tad (1/16") off level front to rear when I first began to fill it. I was worried given past tragedies, but my husband accurately predicted that it would be level by the time it was filled. Turns out he was dead-on! I was dually impressed. The floorboards & supporting beams sank under the weight of the tank/stand (for lack of a less ominous way to put it) farther from the wall than they did closer to it, thus negating the 1/16" and resulting in near perfect level front to rear. I never would've thought of that, but I will from now on.

Anyways, thanks again, Everyone, for all the thought & input.


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