Emissivity is defined as the fraction of energy being emitted relative to that emitted by a thermally black surface and is a measure of how efficiently and quickly a surface emits absorbed heat . Emissivity is defined on a decimal scale between 0 to 1. Emissivity of 1 represent a perfect emissive material that emit 100% of heat while emissivity of 0 represent a surface that absorb 100% of heat.

This article is aimed to provide typical values for roof emissivity based on type of the roof and roof construction material. Users can change roof emissivity value in cove.tool web app under baseline energy page. Roof emissivity is set to 0.9 by default. Users can change this value based on roof material of choice for their projects.

The following table provides typical values adopted from ASHRAE Handbook – Fundamentals version 2021 for roof emissivity value.

The emissivity of green roofs ranges from 0.5 to 0.99 depending on a myriad of factors including season, plant types, water content, leaf area, and more. For accurate modeling of the green roofs emissivity we recommend confirming the project specific value with an engineer or the manufacturer.