Have to say that my experience last August (08) was that the bank (Halifax) would only accept the valuation pre refurbishment.
I was in the position of owning the house without a mortgage but I wanted to raise around 250k to undertake major building work....basically the house was to be completely gutted and an extension of 54 sq metres put on.
The valuation pre refurb was 480,000. When I got mortgage approval it was at the pertaining rate for LTVs of less than 75% but greater than 50%. I did my best to argue that spending 250,000 on the house would undoubtedly increase the valuation to over 500,000 and therefore I qualified for the rate relating to less than 50% LTV. There was no way they would agree to this under any circumstances.
I did take the mortgage from them in the end anyway as their rate was so competitive and I must have got one of the last trackers but it still rankles a little bit.
OP, I hope it works out for you, I really do, but sadly my experience was not the same as Vanilla's.