A green roof, a vegetative layer grown on a building roof, has become increasingly popular in recent years due to its environmental benefits. A large number of research studies have been conducted to evaluate the performance and benefits of green roofs through experiments and modeling analysis. However, only a few studies in the past literature addressed the energy performance of green roofs in cold climates. This paper, therefore, aimed to fill this gap by evaluating their energy performance in cold climates through experiments and modeling. The test bed was the green roof located on the roof of Schleman Hall on the Purdue University campus in West Lafayette, Indiana. It is equipped with a data logger and various sensors for measuring soil temperature, water content, etc. The experiment presented in this paper focuses on the thermal performance of green roof in cold climates and the impact of the phase change of water in the growth medium on the thermal performance of green roof. A transient numerical thermal model was developed and validated by the experimental data. The paper provides new insight of the impact of the phase change of water in green roofs on their thermal performance as well as their thermal characteristics. (C) 2016 Elsevier B.V. All rights reserved.