bank valuation will differ from bank to bank based on their valuers' interpretation. for BSD, you will pay based on your offer price which is accepted by the seller. the bank which you are taking the mortgage loan from will then get a valuer to perform the valuation again and this value will be the agreed buying/selling price of the house. don try to get a higher valuation that what is the agreed price as this would mean you pay more BSD but your bank loan will still be based on the buying/selling price and NOT the valuation. remember that BSD is based on valuation or buying price whichever is higher. the only way your bank will grant you more loan is when your purchase price is higher which does not benefit you at all.
when you need to do recon/A&A, your bank will loan you the money as a construction loan which is different from the mortgage loan. this construction loan will be at a higher interest rate during the construction phase until the TOP/CSC is obtained where it would then be converted to part of your mortgage loan at the lower interest rate. (this is from my understanding, check with your banker if this is the case or not)
now, bank will NOT loan you the full 100% for the recon/A&A. the will loan you usually between 70 to 80 percent of the quotation for the recon/A&A. so this means you will need to fork out CASH for the first 20 to 30 percent of the construction until the milestone is reached where you will start to draw down the construction loan. the repayment for the construction loan will be based on how much is drawn down plus intereste. eg: if your total loan is 500k, and your first draw down is 50k, then you will pay for the installment for this 50k first. if your 2nd drawn down is 100k, then your next installment will be for the 150k which is drawn down and disbursed to the contractor.
before the bank will loan you money for the recon/A&A, you will need to get a quote from the contractor as well as provide the architectural drawings for the house after the recon/A&A. the bank will then get a valuer to value the house again for AFTER recon/A&A based on the architectural drawings. the valuation of the house AFTER recon/A&A MUST be more than the value of the house BEFORE recon/A&A plus the loan amount that you are seeking. eg: current value is 2.7m. you are looking to borrow 500k for recon/A&A, so valuation of the house AFTER recon/A&A must be more than 3.2m.
do note that the minimum value AFTER recon/A&A is determined by the bank. if the value AFTER is lesser than what the bank is looking at, that would mean the bank will loan you less money.
in summary, you are looking at taking 2 loans. mortgage loan for you to buy the house and construction loan for you to renovate the house AFTER you officially take over the house.