I think you're already talking about adding the equivalent of joists (even welding some thick bar across would prob do in lieu of joists for the widths your talking?). Normal widths and the composite stuff is fine. I can't see that DIY casting a heavy slab of concrete up there is going to be a good idea personally!Not had any luck finding any thinner than timber decking and my experience of composite stuff is it's pretty dire and floppy.
Leaning towards @Pete. and @8ob's suggestion of shuttering in some concrete. The door is unlikely to be open when it's wet as my desk is/will be right next to it so that's less of an issue.
The point is those would be within the steel structure. Find me some decking composite or timber that's less than 20mm thick and we're onto a winner (that's the absolute maximum as that's the front lip of the door cill). I don't want to be planing down lengths to reduce them.I think you're already talking about adding the equivalent of joists (even welding some thick bar across would prob do in lieu of joists for the widths your talking?). Normal widths and the composite stuff is fine. I can't see that DIY casting a heavy slab of concrete up there is going to be a good idea personally!

Not composite but there's stuff out there.The point is those would be within the steel structure. Find me some decking composite or timber that's less than 20mm thick and we're onto a winner (that's the absolute maximum as that's the front lip of the door cill). I don't want to be planing down lengths to reduce them.
In fact a floated concrete floor would do thinking about it, why bother even tiling it![]()
the mistake has been done you either use what you can or you take apart what you have builtThe point is those would be within the steel structure. Find me some decking composite or timber that's less than 20mm thick and we're onto a winner (that's the absolute maximum as that's the front lip of the door cill). I don't want to be planing down lengths to reduce them.
In fact a floated concrete floor would do thinking about it, why bother even tiling it![]()
Not so ideal for dogs feet though..the other way is either steel grating or grp grating also level with the tops of your girders within the walls
