Section 4.55 Alteration - Do I need one?

We have DA approval for a renovation project but haven't started yet. We are considering a few alterations to our original plan but I can't determine if I require a Section 4.55 application (NSW). The council feedback is vague and the documentation I found isn't much clearer either.

The changes we are considering are:

1. change the design of an outdoor staircase from one style to another (less bulky and with railings)
2. change the roof material from Nulok tiles to architectural metal sheets
3. reduce the roof size and exclude roof over entertainment area


I am pretty sure item 3 requires a 4.55 because the structural requirements change and our plans would need to be updated. I understand and accept this.

But what about item 1 and 2, if they still comply with all the requirements? A 4.55 applications is not only time consuming but the designer, engineer and council all asks for fees of course and the changes may not be worth it in the end.

Appreciate any advise as to what exactly requires a section 4.55 application.

Thanks and regards
Chris