Generating an optimal planning of building retrofit for a portfolio of buildings may include providing a plurality of objective functions that may be selected for maximizing cost reduction, maximizing green house gas emission reduction, or maximizing energy reduction, or combinations thereof. The objective function may be solved based on information including at least a retrofit cost for retrofitting a building, payback period specifying the length of time needed to recover the retrofit cost, a budget available for retrofitting the building, expected price of energy, estimated energy savings from retrofitting and estimated green house gas emission from retrofitting. The planning of building retrofit may be generated based on the solutions of one or more of the objective functions, which may provide for an optimal plan of building retrofit.