Joist sizes for decking

Hi,

We are looking to add some decking in our garden to an area up to 2.9m x 7.9m, this is the largest area so it may be smaller. Currently there is a solid hardcore base topped with gravel and some slabs. I did plan on using 150mm x 47mm for the joists and frame but this may be a bit high as there is not much of a gap from the patio doors to the stones. Would 100mm be suitable else I would need to clear a layer of stones from the top.

I plan on using 400mm spacings and aboit a 25mm board on top.

Thanks

I'm doing a new decking at the moment but it is over the existing grass/soil level. I am going to use 47mm x 95mm joists on 450mm to 500mm centres but I think the crucial issue is how close your supporting posts are underneath. I'm planning on having wood pillars every 1000mm to 1200mm in both directions. The four corner pillars (100mm x 100mm posts) will be dug in and concreted, the rest (75mm x 75mm posts) will probably be stood on small slabs laid on concrete to level once the topsoil has been removed.

Having looked at C16/C24 joist support tables this should be more than adequate unless you are planning on having some serious weight on your deck.

Richard