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Hi ,

Im planning on making a heavy duty storage shelf/ mezzanine floor to go at the rear of a barn. Dimensions are 15 ft wide x 8 ft deep and approx 8ft above ground.

The floor is concrete. My idea was to use 4x4 posts sitting in Catnic feet bolted to the concrete. I was intending using 6x2 cross bearers and 4x2 joists topped of with 18mm ply.

My question is will the 4x4 posts be strong enough and what should be the spacing, additionally how far apart should the joists be, 15 inchs perhaps? Weight on floor will be about half a ton evenly spread.

Any tips would be great.

I would use six of the 4x4 posts (two in the centre, two at each end, obviously) and I would use two 8x2's running the 15ft with 6x2 joists at 16" centres (and I would use joist hangers as well for a more elegant structure, even if it is only a barn...)

You say the weight will be only half a ton, but who knows what the future may bring ?

Another option would be to use a steel and two legs at the front, a wallplate with joist hangers at the back, then you only have 8' to worry about.

I did consider using steel posts however im unsure of the cost. Going width ways i was going to put 3 posts, therefore 5ft apart, front and rear and in the middle so therefore 9 posts in all. The wholething is virtually freestanding, the only thing ive got to bolt onto is one rsj upright.

Also could you not fix a ledger against the barn wall, like you would with decking- http://www.ultimatehandyman.co.uk/diy/d ... fixing.htm

Cant fix a ledger. Basically its one of those steel framed buildings with metal cladding, the only thing with any strength is the rsj uprights, one each corner and one in the middle.
My biggest worry was whether a 4x4 post, all be it 9 of them, would retain the weight and whether or not the floor would be top heavy and flex the posts as they would be 8 ft tall.

I am obviously missing something here, but if you are going to put posts at 5ft centres, wouldn't that be a total of 12 posts rather than 9?

personally I still think 6 posts would be ample to carry half a ton, as long as you beefed up the joist sizes .

hiking bear wrote:I did consider using steel posts however im unsure of the cost. Going width ways i was going to put 3 posts, therefore 5ft apart, front and rear and in the middle so therefore 9 posts in all. The wholething is virtually freestanding, the only thing ive got to bolt onto is one rsj upright.

as murmac says that would be 12 post hikingbear


0ft 5ft 10ft and 15ft x3=12

with 12 posts, your original choice of 6x2's and 4x2's would be fine.

using 6 posts and beefier joists would give you a more usable space un derneath the platform, however

Yes your correct, it is 12 posts and not 9.

[quote="hiking bear"]Cant fix a ledger. Basically its one of those steel framed buildings with metal cladding, the only thing with any strength is the rsj uprights, one each corner and one in the middle.
quote]

You could coach bolt a timber to this, and use joist hangers fixed to that for the joists?