If you haven't already read it see our Buying Property Subject to Finance? Your Rights and Obligations blog post.
If you need to obtain a loan to buy the house then you must place a finance clause on the contract. REIQ and ADL contracts both have special areas to write in a finance clause and each have similar requirements to ensure the contract becomes "subject to finance". Make sure you discuss with your bank how long it will take for them to give you a letter of unconditional approval as you will need to keep that in mind when writing it into the contract. For example, if the bank needs 14 days then make sure that is the timeframe you place on the contract. If you sign a contract without a finance clause and you need to obtain finance and your application is unsuccessful the seller can terminate the contract, keep your deposit and sue you for costs and losses if they resell it to another buyer at a lower price. Therefore it is essential to make sure you are protected.