The radical restructuring of the German utility giants RWE and E.ON in the wake of Germany's shift to renewable energy motivates the need of a formal model of corporate social responsible (CSR) investment appraisal with environmental externalities. We offer in this paper a model that uses the tools of decision analysis to value the option to postpone the project. We show that adding a CSR dimension to projects generating negative environmental externalities can induce the firm to invest immediately, whereas it always postpones projects without CSR activities. According to the project's attributes, the paper also determines the optimal level of effort in CSR.