One thought for you - if you are using 5mm+ ceramic tiles for your splashback you don't need to increase the heat resistance of the sheeting behind them; this only needs to be done for glass and stainless steel splash's.
There is some information in the notes of point 3 regarding fire retardant requirements in this document:
http://www.esv.vic.gov.au/Portals/0/...clearances.pdf
Cheers,
Earl