Floor advice for a storage shed

[aeroden]

G'day guys,

I'm gathering mental strength to embark on building a 2x3m storage shed in my backyard - a properly insulated one that will stay condensation free and not too cooked under Melbourne sun.

I really like this simple design: https://www.youtube.com/watch?v=FD0_2aO_3so
So I would like to take it as a basis and add sarking, insulation, and colorbond roof/cladding, plus put the beams on posts instead of ground.

Where I'm stuck is the flooring material. The guy in the video uses treated OSB which we don't have here in AU.

What would you recommend?- The shed base is essentially the same the one for a deck. Colorbond cladding will overhang below the floor level all the way to cover the beams, so the floor won't be exposed to direct rain - only(?) to moisture coming off the ground beneath it, which is my main concern.

Here are the options I've researched so far.

1. Structaflor H2 Treated Red/Yellow tongue
2. Same as 1 but to paint the bottom with a couple of layers of bitumen paint. My concern is that edges of the joints won't be fully sealed and moisture will get in overtime, and start swelling.
3. Same as 2 but also put a layer of sarking on top of joists before layering the yellow-tongue. My concern is that sarking will sag overtime.
4. Use compressed cement flooring board. Never worked with those before. Quite expensive - will be more than double the cost of the yellow/red tongue. My concern is that it will week moisture overtime, unless I seal it at the bottom which brings me back to square one

Your advice would be highly appreciated.

[droog]

A couple of points to consider.
H2 is designed for well ventilated areas and helps protect against insect attack https://www.atpine.com.au/treated-pi...aIm4pnA7qEevEv

If you are building this close to the ground you need moisture protection H2 is no advantage. Likewise the compressed cement offers no advantage unless the framing is moisture resistant as well.

Another point is that most garden sheds are not designed to stop all water ingress. The bottom rail on the wall sheets is even both sides as water builds in the channel it can spill out both sides, this can be resolved for the walls with a flashing that comes up the inside however this flashing is exposed at the door opening making a trip hazard and will mean lifting things over the flashing.

I have a shed on a raised platform using C channel and sealed yellow tongue, I consider that the floor is limited in lifespan and will need replacing long term.

I consider there are two long term options, concrete slab with a recessed edge, or don’t start with a “garden shed” to start with.

[aeroden]

Thanks for the quick response.

If you are building this close to the ground you need moisture protection H2 is no advantage. Likewise the compressed cement offers no advantage unless the framing is moisture resistant as well.

Yes, I plan to use H3 treated pine for the floor joists.

Another point is that most garden sheds are not designed to stop all water ingress. The bottom rail on the wall sheets is even both sides as water builds in the channel it can spill out both sides, this can be resolved for the walls with a flashing that comes up the inside however this flashing is exposed at the door opening making a trip hazard and will mean lifting things over the flashing.

I don't intend to buy a green shed kit (e.g. from Bunning), if that's what you mean. I'd like to frame one and clad with colorbond, properly. E.g. like here.

I have a shed on a raised platform using C channel and sealed yellow tongue, I consider that the floor is limited in lifespan and will need replacing long term.

How did you seal yellow tongue?

[droog]

Thanks for the quick response.


Yes, I plan to use H3 treated pine for the floor joists.


I don't intend to buy a green shed kit (e.g. from Bunning), if that's what you mean. I'd like to frame one and clad with colorbond, properly. E.g. like here.


How did you seal yellow tongue?

H3 still expects to be clear of the ground but exposed to some weather, I would be looking at H4 or better if its going to be close to the ground and with limited ventilation.
A proper framed and clad shed you will be able to keep the weather out.
I used a drum of left over concrete sealer on the yellowtongue.

For what you are proposing I would get a slab poured with a vapour barrier underneath, even if you just batten the slab and lay a timber floor on that.

[aeroden]

I can't find any H4 lvl structural timber - only stuff like pine sleepers or posts (i.e. for ground-contact use). I thought using H3 KD structured timber and slapping a layer of bitumen paint on top (once the foundation frame is assembled)

Slab out of question due to cost and the uneven ground (i.e. will require a small retention wall which is even more cost).

[ErrolFlynn]

Slab out of question.

Put it on posts. Perfect for uneven ground. And the dog will love being under there in summer.