Is untreated wood OK in this situation?

[smp50]

I'm building a shed/summer house kind of thing. I have the foundations done, from top to bottom we have:

--75mm fence posts as bearers
--square of plastic sheet
--shims (roof felt, scraps of wood)
--100-200mm of concrete blocks or bricks
--thin layer of gravel
--soil

There are five fence posts each supported at three points, and the area they mark out is 3x2m

I'll be building the floor frame out of something like 2x3" and want to know if this, too, must be factory pressure treated. There will be no ground contact and no rain should get to it. It is far easier for me to acquire untreated timber, as it's what my local stockist has and I can avoid the £20 delivery fee from other places.

Should it be fairly safe with that kind of ventilation or might the area under the shed remain too humid? Has anyone here got by alright with untreated shed bases?

The floor on top of the frame might be OSB or improvised out of pallet scraps or whatever I can find.

thanks,

 

[kbdiy]

There is no 'must be pressure treated' but of course it is recommended that it is. The alternative is to use untreated and add your own treatment - it won't be as effective as pressure treated, but then it is only a shed.

 

[WalksWithTurkeys]

The plastic sheet might allow water to pool beneath the wood. I'd put brick betwee the two allowing damp to wick away from the wood.

 

[smp50]

Ok, thanks. I might do away with the plastic altogether as there isn't room for two brick/concrete pieces on most of the piers. I got some treated wood for the floor frame, now I need to find out what nails are safe to use with it. I just get mine from bins in the local hardware store, no details on them.