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post #1 of 13 (permalink) Old 03-05-2014, 06:16 PM Thread Starter
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Floor Support

I'll be getting a 150g tank in a month and I had originally planned on beefing up my floor joists but after going down in to the crawl space I am unsure if I need to. I thought my joists were 2x6 48" OC but they are actually 4x8 48" OC. The actual sub floor is 1.25 inch thick ply. Everything is in good shape other than being a bit bouncy (apparently the 48" OC thing was a west coast 70's experiment ). The joists have a total span of 12' but are supported by posts at 6'.

The tank will be on a perimeter wall perpendicular to the joists and will actually run over two joists. Right now I'm leaning towards not screwing with the floor and focusing on building the stand. What do you guys think?

If it matters I'm using 1/2" ply as the base of the stand in hopes of better distributing the weight.
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post #2 of 13 (permalink) Old 03-05-2014, 06:32 PM
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I'd say your 4x8 joists are plenty to support 1250 pounds or so worth of water and aquarium stand. Your goal should be to get the weight distributed onto the two joists below.
I suggest that you forget about using plywood to distribute that weight and consider something like a couple of 2x4s that span the stand's base. If you already have a stand, you could build a flat box out of 2x4's (or 2x6's if you like over-doing things), put a plywood top on it, and set your stand on top of the whole thing - sort of like a very short pedestal.
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post #3 of 13 (permalink) Old 03-05-2014, 09:52 PM
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Several factors here and it sounds like you have a good idea of what it takes. Going to the crawlspace to look puts you one up on many!
Assuming you mean for the tank to be along an outside wall so that the ends of the beams are supported only a foot or so away from the tank center? And then they have support again about six feet further into the house?
A tank setting on two of these joists will be no problem, in my opinion.
Then there is the question of what if I'm wrong? Will it be a sudden collapse that wrecks the house? NO! If we are totally wrong and it does begin to settle, it will be a gradual slow moving tilt to the front going from the wall toward the center of the room. You may notice the water line getting weird, if the worst case comes about.
What would you need to do then? Likely you would need to crawl in that old dirty crawlspace again and take a jack to support the sagging floor.

Sounds about like what you would need to do now except you would know for sure it was needed. I let the sleeping dog lie quietly until action is needed. But then I'm one guessing you will never need the action!
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post #4 of 13 (permalink) Old 03-06-2014, 01:13 AM
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Quote:
Originally Posted by PapHater View Post
I'll be getting a 150g tank in a month and I had originally planned on beefing up my floor joists but after going down in to the crawl space I am unsure if I need to. I thought my joists were 2x6 48" OC but they are actually 4x8 48" OC. The actual sub floor is 1.25 inch thick ply. Everything is in good shape other than being a bit bouncy (apparently the 48" OC thing was a west coast 70's experiment ). The joists have a total span of 12' but are supported by posts at 6'.

The tank will be on a perimeter wall perpendicular to the joists and will actually run over two joists. Right now I'm leaning towards not screwing with the floor and focusing on building the stand. What do you guys think?

If it matters I'm using 1/2" ply as the base of the stand in hopes of better distributing the weight.
That is a problem. A BIG problem.

The intelligent, prudent, err on the side of caution proper thing to do is to consult a structural engineer.

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post #5 of 13 (permalink) Old 03-06-2014, 01:34 AM
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I don't know much about structural engineering and I've only ever glanced under the crawlspace I live in now, but if my floor was bouncy I would investigate further, but that is just my opinion. Better safe then sorry later I like to say. You can still build your stand and get things moving along, but I would think about supporting the area under the crawlspace if you think the specific area needs more attention. Post would probably sink, now that I think about it.. edited out that idea, heh.

Good luck, congrats on the new tank!
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post #6 of 13 (permalink) Old 03-06-2014, 03:23 AM Thread Starter
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That is a problem. A BIG problem.

The intelligent, prudent, err on the side of caution proper thing to do is to consult a structural engineer.
It's not the joists that are bouncy, they are rock solid. It's that the joist are just under 4' apart leaving the over sized ply to span that distance with little support. It's something they did in the 70's and the bounce is common with this type of structure. If the tank was running parallel to the joists I'd be more concerned.

I probably should have said this earlier but I've got a 90g sitting where the 150 will be and it has stayed stable and level since it has been up.
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post #7 of 13 (permalink) Old 03-06-2014, 03:36 AM
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You're putting a lot more stress on the floor. Here's the thing. If it were me, and it's not, I'd have an engineer look at it. But it's not me. And I won't be doing the repairs and cleanup. That floor with 4' between joists isn't rated for all that weight. But again it will be fine from my house.
Piece of mind. Or peace of mind.

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post #8 of 13 (permalink) Old 03-06-2014, 03:36 AM Thread Starter
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Originally Posted by Farm Fish View Post
I'd say your 4x8 joists are plenty to support 1250 pounds or so worth of water and aquarium stand. Your goal should be to get the weight distributed onto the two joists below.
I suggest that you forget about using plywood to distribute that weight and consider something like a couple of 2x4s that span the stand's base. If you already have a stand, you could build a flat box out of 2x4's (or 2x6's if you like over-doing things), put a plywood top on it, and set your stand on top of the whole thing - sort of like a very short pedestal.
I haven't drawn it up in sketchup yet but my plan was to run the plywood as the bottom base and then span the 2x4s on top of the plywood. What do you think of that? My hope was that the plywood would distribute weight over a larger area as opposed to directly under the spans. No idea if that theory will hold water though.
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post #9 of 13 (permalink) Old 03-06-2014, 02:02 PM
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Wow I've never seen 48" centers. Scary as I'm used to 18" as standard with 24" pushing it.
Your joists coming off the header walls are more than strong enough to support the tank however look to where the stands legs are since all the weight will be transmitted through them. If they're at or near the joist then no problem but if their falling in that 48" center then I wouldn't trust the ply to remain solid with no sag for long.
The bouncy part could cause you some problem as some of that bounce will be transmitted to your tank. Look at it this way you won't need a wave maker.
If the bounce proves a problem then you can place support jacks in even after the tank is in place. The other thing you can do is place a bit of clear tape on the outside of the tank at the water level in each corner. That will allow you to assess if the floor is sagging at all over time. Again if a problem begins to show up you can always add jacks then.
The use of screw jacks will allow you to adjust them as necessary over time.
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post #10 of 13 (permalink) Old 03-06-2014, 02:44 PM
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Flat plywood won't do much to distribute weight. I suggest that you just rely on 2x4s for that and attach your plywood sheet to the top of the 2x4s to keep them square.
2x4s will distribute weight much better than plywood, and putting plywood directly on the floor would make it tough for you to dry up any spills. (I think Steve002 is the one that mentioned that in a previous thread..).
Another way to span your joists is to use structural plywood, 3/4" or better, as vertical panels on the front and back of the stand. If you want a door in the front to access the space under your tank, though, it gets sketchy.
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post #11 of 13 (permalink) Old 03-06-2014, 05:19 PM
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i have few questions, and and suggestions.(a photo or two really would help).
you say 4x8? joist? are you sure? that would be (by 70's standards) 3 1/2 x 7 1/4"! most likely quarter sawn oak right?
quarter sawn oak will have a very ruff finish as opposed to a smooth sanded finish! like an SPF joist!
and at 48"oc i can understand the use of 5 quarter ply!! OSB(Oriented Strand Board) or RTD plywood?

crawl space: is it an unfinished floor with fill and stone gravel? or poured concrete?
the posts at the 6 foot intervals:
4x4 or lally column? if it's posted in the middle their must be, i'm guessing. a footer under them?
be it stone or standard 4" concrete floor!

i'd not be so concerned about the bounce(flex), as i would be about the shear of the static load!

150 gal: thats what 6foot long? so to be over three joist you'ed need a 8foot+ base to sit over the end joist
and only have one in the middle!(if you can hit that symmetry).if your only building a 72-74" stand the two joist your sitting over,
would be at best in the middle or off set and not realy supporting the perimeter.

that would very much concern me!!!

oh, and the Filled Weight of a 150 gal is 1800#s not 1250# and thats water only!
after stand/substrait/any rocks, i'd bet your at around 2000#s+!!!

(http://freshaquarium.about.com/od/aq...zesweights.htm)

if it was me, i'd put a hung (simpson strong-tie), dbl 2x8 header between all the 48' oc joist the tank sits on ( be no more then 12in
from the posted 6' point loads you have now) and hang (use a joist hanger) two single joist 16" oc between them to your sill plate!
run a continuous bead of Construction adhesive on top of the 2x you put in to lessen floor squeaks.
that'll save you cost of lumber, useing 12 footers cut in half seeing your only spaning from sill to header, not the full 12 foot.
in my opinion that shoud be fine, for that load.

"my plan was to run the plywood as the bottom base and then span the 2x4s on top of the plywood".
what do you think of that? My hope was that the plywood would distribute weight over a larger area"
as opposed to directly under the spans. No idea if that theory will hold water though."

the ply won't distribute any weight! the 2x sitting perpendicular of the joist is what thats for, go with 2x6 for the base.(on edge)
and top perimeter of the frame.
then consider what your using to cover the frame your making, if it's non structural material you'll need to point load the from the top of the frame down to the joist!
when you build the box. (i would do that anyways) with 2x4s. again put them so the 2x4s sit full on the 2x6 top and bottom perimeter frame!


sorry to be so long winded(lol)
i really do know what i'm talking about structurally.

this is the last house i built (i've been building over 35 years)
11.900 squ ft, 14ft first floor walls, 12ft 2nd, all 2x6, full span TGI floors











this it the stand i built for a(my) 75








this is what i had to do to take the shear force of the load!






e-mail me ([email protected]) and i'd be more than happy to help you anyway i can getting it right!!

take everybody's advice , don't just put that filled tank on that floor just yet!!
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post #12 of 13 (permalink) Old 03-07-2014, 04:01 AM
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Typsy, I've use rough wood like that before. Sometimes it was oak but most of the time it was pine. Generally if it's a rough piece of wood it will be a rough sawn piece true to size. Generally. My grandfather built our house up north in 54 and all the wood is rough sawn. A 2x4 measures 2x4. 2x8 floor joists are a full 2x8.
He could beef up the stand if he covered the 2x4 frame on both sides with plywood. It's called a torsion box and is very strong. (I still wouldn't use it here where joists are 4 feet apart.) BTW you hollow core doors are in effect a torsion box.

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post #13 of 13 (permalink) Old 03-07-2014, 02:18 PM
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I stand corrected; Typsy is right about the weight of a water-filled tank. I was thinking about gasoline the other day and used that weight instead of water. So, if you filled your aquarium with gasoline instead of water it would be considerably lighter, for whatever that's worth.
I still think 2x4s on edge as a base would be adequate to span your floor joists and support the whole tank. 2x6s would give you even better support. You might check to see if the "bounciness" is in your joist or just the unsupported sub-flooring between them: stand about 2 or 3 feet away from your wall near where you want the aquarium to sit and hop up and down while moving from side to side. You might notice that the floor is not bouncy when you're directly above the joists. Have a large friend help you with this. If the floor is bouncy everywhere, including above the joists, then you should consider additional support below like another header and posts below.
I'm no structural engineer but I think Typsy gives good advice about transferring load to your joists by ensuring that your tank weight is supported directly by the 2x4 or 2x6 member at the base, which in turn will transfer the load to your two joists..
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