Wood expansion

[FishTruck]

I am building a room divider tank, that will look like it is a full wall - new home construction. I am trying to figure out the best way to put a tank to ceiling hood over the tank. I can't just frame it from tank rim to joist... wood expansion could crush the tank right?

I could just build a giant hood to rest on the top of the tank - but it might be heavy enough to crush the tank and also, might not look like a true wall - which is what I am going for.

So, I am thinking about suspending the hood from the joists. How much clearance to I need to account for 90 inches of wood expanding and contracting (including the wooden stand)? I know it depends on the grain, the width of the wood, and the species... AND plywood expands less. But in ROUGH terms? 1/2 inch? Remember... I don't want more than necessary, because I have to reach over that to grab corals and rocks in the 30 inch tall tank.

Thanks for your thoughts.

 

[FishTruck]

 

[BornHandy]

For your first question:

Wood expands and contracts along the width of the grain, and almost not at all along the length. Let's imagine 2 different boards...

Both boards are 10 inches wide, and 48 inches tall, and stood up with one end on the ground, and the other end chest high.

Board "A" has the grain from top to bottom, so the movement will slightly change how wide the board is, but have no real impact on how tall it is.

Board "B" has the grain running side to side, so it will measure 10" wide all the time, but may shrink or grow as much as an inch along the 48" measurement.

I hope that makes sense. It is hard to explain without a visual aid...

Looking at your design, expansion and contraction would be inconsequential. Cover it with plywood, and you should be good to go.

2nd question:

As for the tank supporting the weight, glass and acrylic is pretty strong, so unless your canopy is unusually heavy, I wouldn't worry about it resting on the rim (assuming there is some sort of protection for the glass). I have built a few stands with giant canopies over the years, and never had an issue. Here is one of my first....

 

[BornHandy]

On your third question, as you have it laid out, I wouldn't expect more than 1/4" of movement, but I am not sure about the design. I personally wouldn't connect to the rafters unless there was no other way. The big risk being the eventual sag of the ceiling could dump a bunch of weight on the tank, even if you left plenty of room when you first build it.

 

[FishTruck]

On your third question, as you have it laid out, I wouldn't expect more than 1/4" of movement, but I am not sure about the design. I personally wouldn't connect to the rafters unless there was no other way. The big risk being the eventual sag of the ceiling could dump a bunch of weight on the tank, even if you left plenty of room when you first build it.

That was really helpful - I was confusing the width of the board with the width of the grain - now I get it.

- and I didn't even think about the sag of the ceiling -

I could spec a very tall stand (about 12 inches taller than the one in the picture) that rests on the tank and nearly reaches the ceiling. I can put molding around it to hide the gap and then I can give it 3 or 4 inches of clearance. The ceiling will also be supported on 3 of the four corners by studs - so hopefully, it won't sag too much - but if it drops three inches, I should see the walls bowing and splitting before it makes contact with the tank. I can put some black foam or something up there to prevent light or sound from spilling out.

Also, I can ask the builder about ceiling sag, given the framing around the tank, and what I should expect.

 

[Goodair]

You frame doesn't need to be sitting directly over the rim does it? Its not like the tank is gonna act as a support for the wall so you can have it higher, Then your sheetrock, plywood or whatever your using as the face can overhang it.

 

[jt17]

If you design the canopy to fit the outside dimension of the tank and not rest upon the top then any rafter sagging shouldn’t put any downward pressure on the tank.

 

[FishTruck]

If you design the canopy to fit the outside dimension of the tank and not rest upon the top then any rafter sagging shouldn’t put any downward pressure on the tank.

Thanks for helping me think this through.

It does not need to rest on the tank, but if it does, there are some advantages. Namely, minimizing an obstacle to reach over and sealing light, water, noise, and odors inside the canopy.

I also need support strong enough for access doors to offer 100% access to the top of the tank preferably with linear actuators. The doors are collectively 11.5 feet long on the front and back of the tank.

Here is the look that I am going for...