Effects of Vegetative Roof Assembly Waterproofing Design on Thermal and Energy Performance

April 29, 2011
Publication: Building Enclosure Sustainability Symposium 2011, Integrating Design & Building Practices: Proceedings of the 2nd Symposium p 198-209
Author(s): Matthew Normandeau Michael B. Waite

Utilizing an inverted roofing assembly in which insulation is installed above the waterproofing membrane improves the waterproofing performance of vegetative roof assemblies compared to other common design approaches. This improved waterproofing performance is often considered to be sufficiently important to offset the potential for reduced thermal performance of the assembly due to water flow beneath the insulation. However, the reduction in thermal resistance is difficult to quantify, so this design decision may not be fully informed. This paper discusses an analysis of the effects of the preferred inverted roof assembly waterproofing design on the thermal performance of vegetative roof assemblies. A thermal model was developed to evaluate the effect on thermal performance of water flow through a drainage layer beneath the insulation. The thermal model was incorporated into computer energy simulations to evaluate the effects on building energy use.