Subfloor strength for large tank

[Ashish Patel]

I am replacing my new houses floors. The joist actually run the wrong way so I'd be lucky if I had 3 joist under a 400 gallon tank + steel stand. I plan to beef up the joist with 2-4 steel jacks but I don't know if I trust builder grade subflooring on a tank of this size.

Would anyone recommend laying a layer of 3/4 plywood above the subfloor and just having the wood floors going up to the plywood?
Would anything else under the subfloor be required to better distrubt the weight? My house has those new man made joist so budding wood flush against it would not be possible. I may just get an outline of the tank in the basement and see if I can add some support in key spots.

I've tried looking for advice on the big tank threads but most tanks just add ontop of the woodflooring and beef up the basement jacks.

 

[don_chuwish]

I don't think the subfloor thickness is all that critical. What kind of joists do you have, and how far apart are they? In addition to the steel jacks you may be able to add blocking between the joists.

 

[xxkenny90xx]

I don't think the subfloor thickness is all that critical. What kind of joists do you have, and how far apart are they? In addition to the steel jacks you may be able to add blocking between the joists.

This, and maybe add some extra joists right along where your stand will be

 

[Ashish Patel]

I don't think the subfloor thickness is all that critical. What kind of joists do you have, and how far apart are they? In addition to the steel jacks you may be able to add blocking between the joists.

I am not sure closing is this week. I imagine standard 16". The tank will be 36" wide and will sit on only 3 Joist. I want to add something between the joist and intent to figure out exactly where the tank will be above the joist from the basement. This way I can add additional support directly under the pressure points.

 

[Ashish Patel]

I don't think the subfloor thickness is all that critical. What kind of joists do you have, and how far apart are they? In addition to the steel jacks you may be able to add blocking between the joists.

Since I only have 3 joist holding up 6000LB I will be relying on the subfloor more than I'd like. The steel stand also does not help given the pressure the leveling feet put on subfloor is greater and if I don't have any joist under the front and back stand feet I can imagine the cheap builder grade plywood being compromised overtime with water damage.

 

[Ashish Patel]

My Joist look like this. I guess when I figure out the outline I can run these across.

Would 2 Jacks be sufficient or for a tank of this size should I have 4?

 

[Jon Fishman]

You just need to worry about the joists. 400g is going to do nothing in terms of “compressing” your subfloor..... It’s distributed over the entire footprint of your tank.

 

[Ashish Patel]

You just need to worry about the joists. 400g is going to do nothing in terms of “compressing” your subfloor..... It’s distributed over the entire footprint of your tank.

Thanks,

 

[vetteguy53081]

I am replacing my new houses floors. The joist actually run the wrong way so I'd be lucky if I had 3 joist under a 400 gallon tank + steel stand. I plan to beef up the joist with 2-4 steel jacks but I don't know if I trust builder grade subflooring on a tank of this size.

Would anyone recommend laying a layer of 3/4 plywood above the subfloor and just having the wood floors going up to the plywood?
Would anything else under the subfloor be required to better distrubt the weight? My house has those new man made joist so budding wood flush against it would not be possible. I may just get an outline of the tank in the basement and see if I can add some support in key spots.

I've tried looking for advice on the big tank threads but most tanks just add ontop of the woodflooring and beef up the basement jacks.

I have 1" plywood base under my stand.

 

[Ashish Patel]

I am gonna lay a 3/4" plywood regardless as I don't want to look at an unfinished subfloor through the steel stand and want it to be level with the wood flooring

 

[HawaiianReef]

How far away from that wall is your tank?
Is your tank running parallel or perpendicular to the joists?
Engineered joists are rated. They will have a number on them for load ratings. You can look them up. They will have a dead load and a live load rating. You want to know the live load rating for your span. The rating will be at the center of the span. Thats why I ask how far from the wall is your tank.
The blocking is good, but if you'd like to tie them together, you can use a continuous steel strap to go over one joist, then under the next, then over and so on. You must also use a second strap next to the first going in the opposite way. If the first went over, this second strap goes under. The strap also needs to be fastened to the joists with teco nails. This is usually done on new buildings before the subfloor goes in. But it can still be managed post build by using a reciprocating saw (sawzall) and plunge cutting the subfloor just to make a passage between the joist and subfloor. If you feel uncomfortable with a sawzall, you can just chisel away to get the job done. Just dont chisel the joist.
An easier approach, but pricey, is to install a steel I beam.

 

[Ashish Patel]

How far away from that wall is your tank?
Is your tank running parallel or perpendicular to the joists?
Engineered joists are rated. They will have a number on them for load ratings. You can look them up. They will have a dead load and a live load rating. You want to know the live load rating for your span. The rating will be at the center of the span. Thats why I ask how far from the wall is your tank.
The blocking is good, but if you'd like to tie them together, you can use a continuous steel strap to go over one joist, then under the next, then over and so on. You must also use a second strap next to the first going in the opposite way. If the first went over, this second strap goes under. The strap also needs to be fastened to the joists with teco nails. This is usually done on new buildings before the subfloor goes in. But it can still be managed post build by using a reciprocating saw (sawzall) and plunge cutting the subfloor just to make a passage between the joist and subfloor. If you feel uncomfortable with a sawzall, you can just chisel away to get the job done. Just dont chisel the joist.
An easier approach, but pricey, is to install a steel I beam.

Thanks for your advice.. I am handy but when it comes to Joist I have no clue so would not do anything that I am not comfortable with. Tanks gonna be running parallel to the joist so this worries me the most. Once I remove the woodfloors I will mark exactly where the tank sits on the joist. ideally I want the tank 8" away from the wall but will move it out or in depending on how it fits on the 2-3 joist it will sit on. If its only going to be on 2 joist then I would have to add more support spanning the tank. Not sure but I will be asking you for more advice in the coming week

 

[HawaiianReef]

How far are those joists spanning?

 

[HawaiianReef]

I am gonna lay a 3/4" plywood regardless as I don't want to look at an unfinished subfloor through the steel stand and want it to be level with the wood flooring

If you're mainly doing this to distribute the load to the joist, I would recommend using a hardwood like oak, and run that perpendicular to the joist. That would be much stronger than the ply. Oak t&g flooring is also 3/4" thick.

 

[Ashish Patel]

If you're mainly doing this to distribute the load to the joist, I would recommend using a hardwood like oak, and run that perpendicular to the joist. That would be much stronger than the ply. Oak t&g flooring is also 3/4" thick.

I am actually closing on the house on thursday so will get the span. just figured the plywood would be easier but you make a good point. since the floor joist are parallel adding a solid Oak would help distribute it better to the joist.

I found this picture online. figured i can do something similar only with a 2x6 or 2X8?

 

[Billdogg]

That picture is exactly what I would do, but like you asked, I'd use 2x8 instead of steel. Make a sandwiches of 2x8-3/4ply-2x8-3/4ply-2x8 and put one at each end of the tank. Use a couple of floor jacks on each end. (one jack at each end would be enough, but they're cheap so overbuild!)

The plywood in between the 2x8's will prevent any sagging/warping and increase the strength of the support immensely. Glue and screw them all together to make a solid support.

As for underneath the tank/on top of the subfloor - Any good grade of plywood will work just fine although it's probably not necessary. I would use something that will closely match the surrounding floor and give it multiple coats of polyurethane or other waterproof sealer.

Pictures when done!!!

 

[William Mumford]

I would add a few joist hangers to sure up the mounting. And I would do like the picture.

 

[Ashish Patel]

That picture is exactly what I would do, but like you asked, I'd use 2x8 instead of steel. Make a sandwiches of 2x8-3/4ply-2x8-3/4ply-2x8 and put one at each end of the tank. Use a couple of floor jacks on each end. (one jack at each end would be enough, but they're cheap so overbuild!)

The plywood in between the 2x8's will prevent any sagging/warping and increase the strength of the support immensely. Glue and screw them all together to make a solid support.

As for underneath the tank/on top of the subfloor - Any good grade of plywood will work just fine although it's probably not necessary. I would use something that will closely match the surrounding floor and give it multiple coats of polyurethane or other waterproof sealer.

Pictures when done!!!

I was considering 4x4 but this sandwich idea sounds better. Given the tank will be 7feet would it be better to have the jacks 4 or 6 feet apart? This way the pressure of the 4 joist would be centered or spanning every 1.5 feet

 

[Billdogg]

I'd probably put them in about 1' from either end, but that's me. I'm not a structural engineer nor do I play one on TV

I did do the same in my last house, but not until I crack one of the floor joists - I noticed one day that the dining room floor between my 150 and 120 seemed to be getting a little "springy". ;Jawdrop A few lengths of laminated 2x/ply/2x and it was solid as a rock!

 

[Ashish Patel]

I'd probably put them in about 1' from either end, but that's me. I'm not a structural engineer nor do I play one on TV

I did do the same in my last house, but not until I crack one of the floor joists - I noticed one day that the dining room floor between my 150 and 120 seemed to be getting a little "springy". ;Jawdrop A few lengths of laminated 2x/ply/2x and it was solid as a rock!

yea for sure i can see my entire house becoming springy. I figure I'll treat the floor to concrete the same way I would as a tank stand. Symmetrical and good transfer of weight to the concrete floors. I plan on running the 2/8 at least one extra joist given the number of ppl who can be standing in that room could be up to 10-20 at any given time.