gray wrote:
I am about to start on a non raised decking, ie just laid on to
existing paving slabs

I am seeking advice on the pitching of the timber joists. Some
websites say 1.2m others 450mm.

1.2m will allow the boards to spring or bounce, far too wide. I'd go for
500mm or thereabouts with 28mm boards, 450mm with 22mm boards, assuming
noggins are used.

Also advice on pitching of paving slabs under the joists. As I want to
save as many slabs as I can, for another job.

Any advice please ??.

Also I intend to use 4 x 2 as opposed to 6 x 2, is there any reasons
why I shouldn't ??

None at all, as long as they don't have to span any great distance. A 4 x 2
joist will span around 1.8m without support, a 6 x 2 would span nearly 3m.
Where the joist is fully supported on a flat concrete base I've used 3 x 2
and even 2 x 2 in the past.

http://www.medwayhandyman.co.uk/decking_faq.htm might give some more info.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk