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Vincer 03-22-2011 01:26 PM

Adding posts and beam to floor for aquarium
Hi all! I'm glad I found this forum, I've been bugging people on my aquarium forum about the same issue.

I have a 180 gallon aquarium which is now sitting in the garage slowly angering my wife. I want to reinforce the floor where it will sit (the tank, empty is almost 400 lbs. Add water and we hit close to 2000 lbs!)

So after some discussion about sistering the current 2x8 joists (10 foot span from foundation wall to beam) on 16 inch centers, and discussing the need to notch the sisters due to willy-nilly piping/wiring, I've decided the "simplest" solution is to just put in a beam to make the span 5', if not 4' where the tank will sit.

So now i'm looking at a 8' 4x8 (8 feet because the tank is 6 feet long) beam supported by two 4x4 posts probably spaced 6" apart so that the beam will overhand about a foot on each side. I might use a 10' piece, but that doesn't fit in my minivan ;)

The crawlspace is not exactly level (the house is on a hill and the "floor" follows that), and it has rat proofing on it. I don't know how thick the rat proofing (concrete) is, I'm estimating 2 to 3 inches.

So my plan is this;

- Cut out two squares, 16"x 16" which are centered 6 feet part for the footings
- Dig a 16x16 square 12 inches deep for a concrete footing
- pour 2 inches of concrete in each hole
- drop in either two pieces of rebar in the shape of an X, or 4 pieces in the shape of a square (do I even need to do this?)
- Fill up the rest of the hole
- Set a preformed concrete pier (sort of like the Dek-Blocks that you use for free floating deck footings) into the concrete. The pier has metal straps preattached to it.
- Wait for the concrete to harden. I may or may not wait 28 days for it to reach max strength.
- Somehow attach the beam to the joists (simpson metal thingies probably)
- Cut and then fit 4x4 posts under the beam and onto the preformed pier.
- Attach posts to pier with the straps, and attach posts to beam.

Now the questions;

1) The ground is somewhat damp, because I'm on a hill and there is always moisture. I'm assuming that under the house that is the same. The soil is very claylike (from the gardening I've done). This is why I want to pour a concrete footing instead of just placing the pre-formed pier on the ground after cutting away the weak rat proofing. But, do I need a 12 inch deep footing? I'm sure that 12 inches verses 10 or 8 is not going to make much of a difference in terms of labour (me, digging out a few more inches) and a touch more concrete, which is cheap.

2) Do I need the rebar on the bottom? I know it has to be at least 2 inches from the outer edges. X or square?

3) Should I forget the pre-formed pier and just set the post on the poured footing? Or embed an anchor for a metal post foot? It would be a bit cheaper. I was thinking of the pre-formed pier because the other main beam has piers that look similar (posts on a pyramid like pier)

4) I'll be using an SDS rotary hammer to cut out the squares. Or rather I'll drill some holes at the corners and then "perforate" the concrete and then connect the dots with a chisel (or the SDS chisel bit). I don't want to mess up my circular saw or the crawlspace with the dust that will be created by the cut. Is there a better way?

5) Do I have to do something to prevent expansion problems between the poured concrete and the current rat proofing? Like how sidewalks have that fuzzy stuff in the expansion joints? Or can I just pour the concrete and forget about those details?

I know, a lot of questions, but hey, maybe I'll get a lot of answers!

Thanks guys!


jimmy21 03-22-2011 08:03 PM

39 Attachment(s)
sounds like your on the right track, 16x16x12 should be a pretty decent footing. I wouldn't use rebar. Instead just roll up some wire mesh into a circle. Id do 3 of them and put one right in the middle.

rossfingal 03-23-2011 08:59 AM

For what you're doing, with the load you've got - I would consider making the pads/footings larger - 24" x 24" wide - 16 to 24 inches deep.
(Crawling around in a crawl space - busting up concrete - digging it out by
hand - dragging the debris out in a bucket is "So Much Fun" - why not have
as much "Fun" as you can!?! :) )
If you decide to go with 16" x 16" wide, I'd still go at least 16 inches deep
(if not 24").
Since it's not a floor/sidewalk, but a footing/pad - use rebar - 1 layer
in a square - 3 inches off the bottom and 3 inches away from the edges.
I would also put another layer 3 to 4 inches from the top - X pattern.
If you also want to use some mesh - so much the better!
(We'd use both :) )
Instead of a pre-formed pier, to set the posts on - I would use galvanized
post clips, that are anchored in the footings.
I'd probably use 6 X 6 inch, treated posts and at least, double (triple?)
2 X 12's.
Before you set your posts and beam - add blocking between your joists,
directly over the place you're going to install the beam.
After you pour - I'd wait 28 days before you install your posts.
Sounds like a nice aquarium! :)


Vincer 03-23-2011 01:48 PM

Thanks for the replies!

Two very different opinions!

I will add the blocking (before putting in the beam).

I've seen in a few places where people use doubled or tripled up 2x beams instead of 4x wood. Why is that?

I'll look into the necessary Simpson hardware (Since they are at most home stores!) to add the posts. I was thinking of either the

Simpson ABA44 (downward load limit 6000 pounds) which would require an embeded bolt.

OR the

Simpson PB, which you embed directly, and is not a "stand off" so it just attaches the post (and would be cheaper by a few bucks)

Do you really think a 6x post is necessary?

Like you said, since I'll be down there "having fun" the cost of a 6x versus a 4x is not much.

I should mention that the distance from the bottom of the joists to the crawlspace "floot" is probably 3 ft, it's not a full height basement. So if I used doubled up 2x12s that leaves like a 2 foot post (ie; a 4x4 or 4x6 or 6x6 at 2 feet would not be a bank breaker!

I'll consider having more fun down there. Shoot if you are going to do something, you might as well over do it, right? ;)

(The cost of the extra digging versus a 2000 lb fishtank sagging my floor is a no brainer)

One more question. Would you "hang" the beam first, and then cut the posts? Assuming I cut everything properly, what would be the order of assembly? Like if I bought this at Ikea, what would be the first step ... conencting the beam somehow to the joists and then shoving in the posts or nailing in the posts first?

Also, if I screw it up, what would I use for shims to shim up the post (at the bottom, at the beam?)



rossfingal 03-23-2011 02:47 PM


Blocking for sure!

The reason you would construct a beam using multiple 2x's -
it's easier to handle than a solid 4 X 12 - 6 X 12 - you get one 2 X 12 up, then fasten the 2nd and 3rd (16's, screws, bolts, etc.).

With a 6 X 6 post, your three 2 X 12's have a very good bearing surface!
(Also, if you have any pieces left over, they can be useful - can be used to support a vehicle that you might be working on.)

Concrete first - of course!


Hanging the beam is an idea.
Use a couple of pieces of 2 X 4, 2 ft. or 2 1/2 ft. long, fasten them to the
floor joists (nails/screws) get them a plumb as you can.
("Perfect", is acceptable! :) )

Fasten your beam to these 2 X 4's - try to make sure the beam is as tight
to the bottom of the floor joists as possible.
Also, if you drop down pieces of 2 X 4, and these are screwed to the joists
and the beam - you can leave them in place, to help prevent the beam from twisting under load.

Then install the posts - if you have to use shims, to get the posts in tightly (you may have to).
Use pine "S-P-F" or steel.
Do Not use cedar!

If you have any other questions/concerns - let us know!

I have some work I'm involved in - unfortunately, it doesn't entail
crawling around in a crawl space - some people have all the fun!! :)


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