Short Sale Purchase - All Cash Purchase - Converting to Mortgage after Purchase

[Brett Borders]

I am in the process on closing on a short sale. We plan on taking about 3 months to renovate then I would like to get a mortgage on the property. I cannot seem to find any information on if there is a waiting period, am I tied to the purchase price as the home value even if there are significant improvements to the house that raise the market value of the house? I have my numbers below for help with this scenario

Purchase Price: 334k - Cash

Construction Improvements: 150k - Using HELOC funds against current primary house and Rental Properties

Conservative Market Value after Renovations: $550k (Smaller House across the street just sold off market for 610k)

Will there be a new apppraisal when I go to apply for a mortgage or do they take the purchase price of the property? Does the scenario change after a certain time period where we can get a new appraisal? Obviously I would like to get my cash from the purchase/renovation cost.

Any information is appreciated

Thanks

Carter