The Costs and Benefits of Green Roof Retrofits: A Case Study of a Green Roof Installation on Lewis Thomas Laboratory

Abstract

This thesis is an analysis of the potential costs and benefits of a green roof retrofit, using Lewis Thomas Laboratory at Princeton University as a lens through which to analyze the possibility of widespread green roof application on existing buildings. Two green roof types, extensive and intensive, were considered. The first step in the analysis was to assess the building from a structural standpoint and determine whether any reinforcement would be required to support the addition of a green roof; it was found that no critical structural reinforcement would be necessary. The second step was to quantify the environmental benefits of a green roof. In the third step, a lifecycle cost assessment (LCCA) of each green roof type was completed using existing studies and experimental results. Finally, the environmental benefits and lifecycle costs were compared in order to determine the total green roof savings over a 40-year lifecycle period. While the environmental impacts of an intensive green roof exceeded those of an extensive green roof, the extensive green roof would be much cheaper to install and maintain, thus the extensive roof was determined to the be optimal green roof choice for this particular building. The simple payback period for both green roof types was less than one third of the roof lifespan, demonstrating the potential for profitability in green roof implementation going forward, both for Thomas Laboratory and greater urban areas.