The regulations that apply to how your splashback needs to be constructed will depend partially on the materials you choose to use, and partially on basic requirements under the Building Code of Australia.
Materials and regulations
If you're considering a glass splashback, for example, it must comply with the Australia/New Zealand Standard AS/NZS 1288, and should be built from toughened glass. In fact, you'll even need a letter from the architect, designer, glass supplier or glass manufacturer to certify that the glass is suitable for the purpose for which it's been designed. The glass manufacturer or supplier will recommend minimum clearance from the nearest gas burner to the surface of the glass splashback. However, fixing 5mm thick ceramic tiles to the surface will satisfy the necessary requirements.
Splashbacks and gas
Most installation requirements relating to splashbacks have to do with gas. When you consider that many splashbacks will be built behind ovens and other cooking implements, this is an important factor so you don’t burst a gas pipe or blow yourself up.
Combustible splashbacks installed behind open-flame gas cooktops are carefully regulated in order to prevent them from catching or spreading fire. These regulations are specifically contained within the requiremens for the installation of gas appliances. Combustible materials generally include things like acrylic splashbacks, timber splashbacks and similarly susceptible materials. Many builders and designers believe (understandably) that glass and stainless steel are non-combustible materials; however both conduct heat fairly well, and if they're too close to a gas burner they can easily transfer heat to the unprotected substrate material or timber framing behind them - which as you can imagine may easily end in disaster. A clearance between the nearest gas burner to any combustible splashback of 200mm or more means the installation will be fine. Any less than 200mm and you will need your builder to do a little bit of work to make it safe. If you have a stainless steel or glass splashback, you'll need to install a fire resistant board up to the same distance (200mm from the nearest gas burner) behind the glass or stainless steel splashback that complies with the requirements of AS 5601/AG 601 Gas Installations, Appendix C substrate. There are exceptions to this rule - if clear documentation can be supplied that demonstrates that the fixing method will ensure that the temperature of the combustible surface won't exceed 65º Celsius above ambient temperature during normal operation, then a fire resistant board isn't necessary.
Electric cooktops and splashbacks
The same rules don't apply to electric cooktops. If you have a combustible splashback adjacent to an electric cooktop, for example, this has no regulated minimum clearance; however your builder will still need to follow the basic minimum clearance guidelines set out in AG/601.