1st floor plywood subfloor & tank weight

greech

New member
My living room includes an area that used to be a garage. The floor in that room is about 1/2 concrete and 1/2 plywood split right down the middle of the room. I have read many posts on weight capacities but all seem to be related to those wanting tanks on their 2nd floor or homes with basements. The supports underneath the plywood are flush on the ground (at least they should be from what I can see) so there isn't an issue of "suspended" weight like there is in a 2nd floor or above basement application.

I can place the tank on the concrete but it would look better where the plywood is? What concerns if any should I have?

120 gallon tank with sump.
 

thegrun

Team RC
If the supports below the plywood do sit flush on the old concrete slab and are on 16" centers you will not have a problem. How big is the tank? If it is over 150 gallons i would make certain the supports do in fact sit on the slag and are not up on posts. I would add additional posts if it is not on the slab is the tank is over 150 gallons.
 

greech

New member
Thank you, its 120 gallons (4 footer).

Does it matter if the supports run perpendicular or parallel to the tank?
 

DrBoxedWine

New member
*DISCLAIMER**I AM NOT AN ENGINEER** I am just a dude with a friend who is. So take this with a fist sized grain of salt...

A buddy of mine is a structural engineer and he had a look at my house to tell me what sized tank I could put in the living room. It does matter the way the supports are running, you want to have your tank over as many long floor supports as possible to lessen the weight on each. Ideally you want your tank perpendicular to the supports, as this will spread your tank out on more of them. If you have them parallel, then your tank will be over less supports, say 1 or 2. Whereas if you have it perpendicular, it will be over 3 or 4. It also matters how close it so the load bearing walls in the basement. A tank that's directly over or very close to the load bearing wall in the basement can be bigger than a tank that's dead center in between the 2 basement load bearing walls. It's all common sense stuff that i'm guessing you've at least thought of. You may still be just fine, but a 6' 120 gallon tank running perpendicular to the long beams under your floors will spread the weight out over more beams than your 4' 120 gallon.

So, for my house, which is your typical 1950s home with normal supports, he told me that in the living room (where each side of the room is directly over a load bearing wall, and the room is probably 12 feet wide or so) we could put a 240 gallon tank in the middle of the room and be fine. I'd probably still be nervous doing that without adding supports, but it certainly got rid of any fears I had about putting a 6' 125 gallon tank right near a basement load bearing wall.

Do you have a friend who's a structural engineer? I can tell you that's a weight off my mind (and my soon to be wife's) knowing it's not even an issue.

I don't think your issue is the tank falling through the floor or anything major like that. My understanding is more than it can cause permanent sagging over the long run if it's too heavy.

The sad ending to my story is that my house can support more weight than i can talk my fiancee into allowing in the living room, haha.
 

greech

New member
"Dude" disclaimer understood!

So in your house, it sounds like your floor is "suspended" and you're still safe with a tank twice the size of mine? Again, my supports are flush to the ground with plywood over the tops.
 

DrBoxedWine

New member
Yeah we have a basement with tenants living in it, so it's a major concern for us. But yeah my friend took notes of our setup and then ran some numbers and that's what he came up with. If they're flush on the floor below i bet you'd be good.

My other friend used to build houses and he thought it'd be absolutely fine, as well. One way to think about it... say your tank weights 1200 pounds. If you had 6 200 lbs guys all standing right next to each other bunched up, whether or not the floor would hold wouldn't even cross your mind, probably. I used to have a king size water bed on the second floor of my parents house, as well as multiple other houses throughout college without any problems. Before i got my 125 i called my insurance company to make sure a break was covered.

If I were you, i wouldn't sweat it. But if it makes you feel better, have someone look at it, it took my friend maybe 10 minutes to check it all out.
 

thegrun

Team RC
Put it on a outside load baring wall

In this case the floor will not have been built like a standard new construction framed house. The added floor will not be sitting on top of a framed wall or foundation, it is a floating floor and as such its strength is derived from the locations where the new floor joists are in contact with the garage cement floor, the walls will add little or no support. If in fact the joists do sit directly on the slab as Greech believes the floor will have huge weight barring strength. If they are not sitting directly on the floor then the strength is derived from the added plates that the joists rest on. In this case it is very difficult to ascertain the load capacity of the floor without either looking at the framing plan if one exists or to open up the floor to examine the actual framing.
 

greech

New member
That is exactly the case thegrun. From the little I can see, the supports should be sitting directly on the old floor but I do not know their spacing or the direction that they are running. The permiter frame is definitetely floating and is not connected to the slab on the interior or exterior walls. I guess I was mosting concerned if the support boards would have the strength not to buckle between the plywood above and the cement below. it sounds like I should not be concerned with that though.
 

thegrun

Team RC
With a 120 you will not have a problem even if the joists are on 24" centers, regardless of which way they run.
 
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