Building sector in the United States is responsible for 41% of energy consumption, 73% of electricity consumption, and 14% of water consumption. Energy and water consumption of buildings can be significantly reduced by identifying and implementing green building upgrade measures based on available budgets especially in aging buildings which represent 70% of existing buildings in the United States. This paper presents the development of an optimization model that is capable of identifying the optimal selection of building upgrade measures to minimize energy and water consumption of existing buildings while complying with limited upgrade budgets and building operational performance requirements. This optimization model is designed to estimate building energy consumption using energy simulation software packages, is integrated with databases of building products, and performs analysis of replacing existing building fixtures/equipment and installing renewable energy systems during optimization computations to identify the replacement of building products that minimizes energy and water consumption. The model is designed to provide detailed results for building owners, which include specifications for the recommended upgrade measures and their location in the building; required upgrade cost; expected energy and water, operational, and life-cycle cost savings; and expected payback period.