Thread: Advice please - wooden water tank base safety

Should take the load but I would screw rather thn nail. Countersink the screws well below the surface.

Screws rather than nails because they won't work loose and puncture the bottom of your tank.

Hey, thanks for that - I hadn't even thought of the nails working their way up, but it makes sense. That would indeed make a hole in a poly tank very quickly!

Actually, now I'm wondering if I even need to nail the boards down right under where the tank will sit at all. If I nail the planks at each end, the weight on top should keep it pretty firmly anchored to the beams I would assume? Or will I be depending on the decking being regularly nailed to the beams along the whole length for some structural integrity?

Cheers!

Mike

I'd be inclined to use corrugated iron in place of your board top - this will allow rain water to drain away. The boards will rot quite quickly with the constant wet beneath the tank.
I reckon your framework is plenty strong enough.

soth

i screw at edge of frame only using 12g or 14g gal bugle screws and allow a minimum 5mm gap between the boards to allow for timber movement

Personally I dont like the idea of wood under the tank. How long will the tank last, how long the wood. For me it would be a box of sleepers. Inside the box a layer of gravel then weedmat then a layer of sand and the tank on that

Serapax.
I guess you know that 5000ltr is 5 tons. The frame looks ok but I would leave space between the boards to allow water to drain away also some cutouts at the bottom of the frame to stop water pooling on the concrete between the frames. They dont need to be more than about 20mm arch type cutouts. Or sit the frame on pavers at each cross section to get the same result. My other tip is ensure you have any overflow directed well away from the tank. The tank footings will be buggered in no time ( concrete included) if the overflow is allowed to undermine things. Been there done that.
Regards
John

My alarm bells are ringing

From what I can see, within a few days of completing your project the drain under the tank stand will be blocked, and will stay so till the stand rots out and you have to replace it

Ian has a valid point. I should have picked that up.

The idea of corrugated is fine but if you are still going to use timber space the boards as suggested but make sure to anchor each on at least both ends. If not, when placing the tank it could displace the boards. A right pita.

Originally Posted by ian

My alarm bells are ringing

From what I can see, within a few days of completing your project the drain under the tank stand will be blocked, and will stay so till the stand rots out and you have to replace it

The dip in the concrete means that there is a 2 cm gap under the middle of the beams along the length of the drainage line, however I guess if the beams were to bow even this tiny amount, the gap would close.

Perhaps I should chock a small wedge in the gap to keep it open?

Originally Posted by serapax

The dip in the concrete means that there is a 2 cm gap under the middle of the beams along the length of the drainage line, however I guess if the beams were to bow even this tiny amount, the gap would close.

Perhaps I should chock a small wedge in the gap to keep it open?

a 2cm gap will become blocked by leaves in the blink of an eye

Without knowing anything about your yard, I suggest that for adequate drainage, the gap between the frame and the concrete drain needs to be at least 15cm to allow you to get a tool like a hoe in to clear any muck away from the drain. In practice the gap probably needs to be about 300mm so small dogs and cats don't get stuck.

Sitting on the ground as it currently is it'll also trap dampness, especially as it's over a drain, leading to eventual timber rot and corrosion of the fasteners. Lifting it off the ground by 12" or so will greatly increase air circulation and extend it's life span significantly.

You say it'll be covering a "drain hole" in the back yard. It's not on an easement, is it? Also, if there's more than a single pipe running off the pit you'll really, really want a large enough gap to be able to not only access it but to also be able to physically look inside it.

If the pit ever blocks badly enough that you need to get a plumber out to run a ferret through it, the extra access height can save you from several hundred dollars being added to the bill for what amounts to a "nuisance fee."

Timber rot is a non-issue in the life of the tank with H4 pine sub structure (30-50 years) and H3 planking. The drainage area needs to allow water to run freely to the lowest point - the framing as it is in the pic seems to constrain that. Comments about gaps are sensible - depends how much detritus is around and how often it might block. That size and amount of framing will have no problems holding up 5000kgs water + tank itself IMO. Punched nails are unlikely to ever come up, but recessed screws easier and also allows easier dismantling if ever needed. Need to us coated screws to suit TP or SS.

Issue often missed with tanks is how well they are fixed against forces from wind etc when empty or part empty as they can often be. If they are used correctly they should be empty regularly so that the next rainfall re-fills them . . . ie: they should be cycled through empty to full and empty as much as possible (if the aim is to save as much potable tap water as you can). All tanks are subject to movement in wind when empty so that tying down needs to be accounted for in their placement - and that's to the ground or some object well fixed not simply to the wooden stand unless it is well fixed. Planks would not need to be screwed or nailed so long as they are not displaced as the tank goes in - not gunna move far even with 100 litres of water sitting on them.

With most tanks of that size you can empty and move them to gain temporary access if a problem arises, but it's not something you want to do every couple of years!

Do you really need the drain hole(is it connected to drain pipes?), will the water run else where it could cause damage.
If not dont bother just slap her down directly on the concrete as the tank will conform to the shape of the concrete.