15th North American Green Roof Conference: Cities Alive 2017, Seattle, United States Of America, 18 - 21 September 2017, pp.1
A study was conducted in East Lansing, MI, to compare thermal properties of a shallow (5 cm) sedum roof and a deeper (20 cm) roof planted with herbaceous perennials and grasses. Roof sections were instrumented with heat flux sensors, thermocouples, moisture sensors, infrared sensors, and a weather station. Data were collected for a period of one year. During summer, the shallow sedum roof experienced more extreme fluctuations in diurnal substrate temperatures which tended to be warmer during the day, but cooler at night. In contrast, heat gain into the building was greater on the herbaceous roof during the night and early morning. During winter, heat transfer through the sedum portion of the roof was affected more by outside environmental conditions, whereas the herbaceous portion of the roof was stable. Although, the sedum roof exhibited more extremes, during the summer the herbaceous roof acted as a heat sink and experienced more heat entering the building, whereas, it was more efficient during winter as less heat escaped the building. Contrary to conventional logic that plants with high transpiration rates are superior, during the summer months the sedum roof reduced heat gain into the building and subsequent energy requirements for air conditionaing relative to the herbaceous roof. Results presented are a summary of a portion of the work published in the journal Energy and Buildings (5).