While LEED v4 brings with it a variety of new and updated requirements, the largest changes are within the Materials and Resources credit category.
The reason is simple: the materials requirements were no longer reflective of leadership practices, having become, in many respects, mainstream over the years. They did not represent what the latest science considered an adequate assessment of how materials impact the environment and human health, and leading manufacturers and designers were already including additional considerations in their product decisions.
In exploring the updated requirements for materials, a good place to start is with this question: What is LEED v4 trying to achieve?
Christian Cianfrone, Morrison Hershfield Principal and Building Energy Practice Lead, addressed LEED v4's new standards and metrics for energy performance in Canada Green Building Council's 'Toronto Focus' magazine through his cover article 'Getting Ready for LEED v4'.