Joist span

Building a garden office and using piles for the foundations. On top of the piles I'm going to build my base frame however there are two things I'm unsure about. The first is the size of timbers I should use and secondly is the amount of piles/span. I'm considering either 4 or 5 by 2" timbers and wondered if piles every 100cm would be ok? I'm going to have the timbers spaced every 60cm so a celotex sheet cut in half will fit and will run t&g chipboard across the joists but would appreciate someone's advice as I really don't want the floor to flex.

Thanks guys

Flexing is L/240, L360, or higher, the higher the less flexing.
For L/360, if the span, L, is 36 'units' then the midspan deflection is 0.1 L. If L/360 is too bouncy then go to L/480 or higher.

It depends on the modulus of elasticity for the material and the shape of the material. The Engineering toolbox site can help you with this.

Sorry that's confused the hell out of me.

I basically have a 3.2m run and I want to know how many piles I'll need using either 4 or 5 by 2

for anyone looking at this thread, found this on another site which helped me...

http://www.ebuild.co.uk/topic/9219-what-size-floor-joists-do-i-need/