Decking advice please

[TheCorner]

We have a large area at the bottom of our garden which is currently a 3 large stepped area. All levels are 6 metres x 2 metres with a 15cm drop after each step.

It is covered in small pebbles with membrane underneath then dolomite under that.

I want to cover the lot with decking at the same level.

My questions are:

How far apart should my support posts be and what size?
What size beams should I use?
How far into the dolomite am I going to have to dig before I put in the posts?

Also, B&Q are selling Deck boards at half price this week so I could get my 36 sq metres for about:

£360 using 2400mm x 120mm x 25mm or
£416 using 4800mm x 144mm x 28mm

Which would I be better off getting?

Thanks for taking time to read and helping if you can.

TC

 

[r896neo]

I have never seen 28 or even 25mm decking anywhere other than a diy shed. Any timber or builders merchant will have 32mm and will probably be the same price.

Get the closest board to fit your sizes for less cutting and wastage. A timber yard should have 4.2 4.8 and easily get 3.6 or even probably 5.1

Use 100mm posts concreted in 450mm deep.

For joists use 6x2's, same rule applied waste wise and getting the right size.

 

[TheCorner]

I have never seen 28 or even 25mm decking anywhere other than a diy shed.

http://www.diy.com/nav/garden/fenci...sible-Deck-Board-L-2400-W-120-T-25mm-11117879

It has half decent reviews for the price.

 

[r896neo]

How many reviews are posted 5 years later?