Word of thought in New Zealand once you have fully completed the Renovation generally you can approach a reputable Valuer and have them revalue your home. Have before and after pictures that you can show them, it helps in some cases as they do not know what it was like before. Also find a valuer that knows the area as they will be in a far better position to see the transformation and give a more realistic valuation, Over valuation to gain Refinance is a sure way to get knocked back. Then approach your bank/lender. It may not always work but you have a better chance of success armed with the right information.