How to build a new garden shed on old slab?

[FrantzJosef]

Hi, There's lots of advice on this topic online already but I find I still need some extra input. So hope you can help. Ive just demolished an old kit form tin shed which was about 3 x 4.5 m on a slab which is still good. 

Im trying to keep height and size within regs (3m high and 20m footprint so about 5.4 x 3.6 for new shed ). Since the new shed will cover more ground than existing slab i will use some stirrups set in new concrete for the outliers and other will be set on dynabolted stirrups (height-adjustable as necessary) on old concrete .

Im keen to keep the height within regulations and that means im looking for the minimum amount of space under floor joists , height-adjusted as necessary for uneven concrete surface. Flooring will likely be Structsflor H2 treated yellow tongue 19mm (possibly 22mm) thick 3600 x 800.  It will be lightweight structure and storing mostly light to moderate weight material. Dimensions are 5400 x 3600 with joists running the 5400 length and the 3600 long structa flor sheets at right angle to the 5400 length and at 600 centres. 

So Q's: 1.  Instead of using bearers and then joists could I just use joists with joist ends locked together with a rim joist and if so what would be the best joist dimension to use (once again not going too deep, max 150 but if I could do it with 100 x say 63 that would be better) ? Is hardwood an option?

Q 2. Since Im trying to keep height low Im thinking of using LVL E13 H3 treated LOSP for the joists.  Can you advise on what size LVLs or treated pine joists would be best. There will be moisture underneath from time to time but there will be air flow also and the joists wont be in water. Im in north NSW, coastal.

Thank you Frantz 

[MitchellMc]

Hi @FrantzJosef,

If you are creating a single-level base, the calibre of the joist is determined by how often you support it. Typically, you'd use something like 140 x 45mm, but you could potentially use 90 x 45mm, but you'd need to support it more often. Doubling up the 90 x 45mm could be a way to get by with the smaller height. Hardwood is certainly an option and has a greater span than Pine.

LVL's are a good option, which will typically outspan Pine and Hardwood. Once again, you could get away with a 90 x 45mm, but you'll need more of them and support them at more frequent increments. 

Are you building this shed from the ground up? If so, I would encourage you to enlist the services of a designer or engineer to produce plans for your build. They'll be able to determine the minimum acceptable timber sizes for your specific build.

Please let me know if you have any questions.

Mitchell

[FrantzJosef]

Hi MitchellMc, quick response  and very helpful so Thanks!

Yes shed is being built from ground up so appreciate suggestion re enlisting pro help. 

Also I can beef up joists by using more stirrups. 

I'll probably go with appropriately treated LVLs. I plan to send some photos as shed evolves. Cheers, Frantz