BCA change of building category

Help needed please. I’m going to try to make it short but it’s quite complex!
My neighbour and I share a dual occupancy dwelling. Her unit upstairs and me downstairs. We got a DA approved for extension to boundaries and extension of my neighbours space in the roof and we have just appointed a builder. We are now recruiting a Certifier who has just come back to us with concerns about the design not meeting the BCA standards. By adding a section upstairs we are changing the building type from 1 (residential) to type 2 (multi occupancy). The certifier says that with the design that is now less than 3m from the boundary, we need to replace our aluminium bifold doors onto courtyard and balcony (and windows to the side) with self closing or automatic closing with external wetting sprinklers for fire resistance level. We are struggling to understand how we got to this point without previous warning. It just does not make any sense to have this kind of doors to access a courtyard or a balcony in a high density area (Manly NsW). Has anyone had a similar problem and can share their advice please? We will be going to a BCA consultant but any advice / experience from this group would be greatly appreciated please.

I think our architect did not realise that the design will create a change of classification. It is already a three storey with a mezzanine on the third floor. My neighbour is extending that mezzanine to create an extra bedroom. The building height is not changing. But I guess we are adding surface and openings.

Thanks for any advice.