Alternative decking joist ?

[Housemartin]

Hi I am looking for an alternative decking joist for a deck I will be constructing soon . It will be on three levels the lowest of which is partially resting on concrete and needs to be approximately 88mm high (50mm thick joist plus the deck) as this does not give much of an air gap my ideal solution would be some kind of plastic joist which I can screw directly onto the concrete. Does anyone have any ideas as to what I could use or other cheap alternatives that I can screw decking onto easily?

[The Medway Handyman]

In a situation where the joist rests on concrete I lay the joist on lengths of DPC.

As long as you have a suitable gap between boards it will have enough ventilation.

Assuming a 28mm deck board + a 47mm x 47mm joist you still have 13mm under the joist anyway.

[Housemartin]

So you would raise the joist up off the concrete slightly,and would that be a bitumen based type DPC or just the thin plastic type?

[The Medway Handyman]

Always best to keep them off the floor if you can. I tend to build the frame first & then level it using the noggins - placed on plastic DPC. The noggins don't have to be flush with the top of the joists.