It is likely that applying for Council approval to carry out significant building work would trigger a requirement to bring the units up to current standards regarding the fire isolation of each unit. Presumably current sound insulation requirements would also apply. Our Technical Guides on multi-residential construction will give you an idea of today's techniques. The Guides can be downloaded from our website via this link https://www.woodsolutions.com.au/publications.

We suggest you contact Colin MacKenzie at MacKenzie Consulting. You can visit his website via this link https://timberexpert.com.au/services/expert-support, or contact Colin by email at colin@timberexpert.com.au. If Colin is unable to assist it is likely he could recommend someone in the locality. It will be necessary to know the species of timber, since different species have different strength properties. 

The installation of flooring over a concrete slab is covered in our Technical Design Guide #09 which can be downloaded from our website via this link https://www.woodsolutions.com.au/publications. If the moisture barrier on top of the slab is a polyethylene ('plastic') membrane, fixings will generally not compromise its effect since the membrane will be gripped tightly around the fastener at the point of penetration. However, there is a risk of the membrane tearing during installation of battens.