wooden decking on balconies

[Martyn]

I'm seeing a lot of social landlords replacing the timber decking elements of their steel framed balconies with aluminium decking systems. They are doing this on lots of their smaller buildings, not just the ones over 17m etc. Then I noticed a 4 storey new build going up nearby, which were installing wooden decking on wooden joists.

What is the law around this?  We are looking to replace our decking on our 15m/5 storey building, simply because it's reached the end of it's life anyway. Can we replace it with Class 0 spray-treated timber decking, or is Aluminium the only way to go? Are there any other options eg composite decking

Thanks!