building wooden decking balcony on steel frame

[cobba]

I am building a small balcony on a flat roof; I have had a galvanised steel frame for this built and installed; I will be attaching wooden decking to this for the floor area.

To do this I will be first attaching 4"x2" joists/battens to the steel frame, and then screwing the decking to those battens.

Question - does the decking need to be raised above the steel frame where it crosses it?
ie Should I fix the 4x2 battens so that the decking will lie directly on top of the steel frame where it crosses it, or should I fix the battens so that the decking will be raised (say 10mm) above the steel frame so there is no contact. ie does it matter if the decking is directly in contact with galvanised steel frame; is that likely to encourage rotting?

 

[masona]

I would say it's best to run another timber bearer onto the steel with gutter bolts then decking on top saving you having to drilling into the steel for each decking. Also a bonus would be that the timber is pressured treated such as forest pine which is guarantee against rot/decay for 15 yrs, you could also run a sealant on the bottom of the bearer to prevent rain underneath.

 

[cobba]

thanks, thats useful,

Another question - is it necessary to build in a 1:100 gradient into a decking to allow for rain water run off or does that not really matter?

 

[masona]

Yes, it's a good idea to keep the rain off it. Just make sure it's not level

Ideally the decking timber grooves running away unless the decking timber is flat.