Effect of substrate depth, vegetation type, and season on green roof thermal properties 17 18 19 20 21 22 23 24 25 26 Abstract 27 28It is generally accepted that green roofs can influence thermal properties of a building, but 29 there is some disagreement on the role that substrate depth and plant species plays in this equation. 30A study was conducted over a second floor roof in East Lansing, MI, comparing prevegetated mats of 31 a mixture of sedum (depth = 5 cm) to a deeper roof (depth = 20 cm) planted with a mixture of 17 32 herbaceous perennials and grasses. Both roof sections were instrumented with heat flux sensors, 33 thermocouples, moisture sensors, and infrared sensors, and ambient weather conditions were also 34 continuously recorded by a weather station located on the roof. Data were collected for the period of 35almost a year to cover all four seasons. Also, the roofs were well established and had reached near 36 100% plant coverage by the time data collection commenced two years after planting. Most of the 37 differences in temperatures and heat flux through the roof occurred during the summer or winter. 38During summer, the shallow sedum roof experienced more extreme fluctuations in diurnal substrate 39 temperatures which tended to be warmer during the day, but cooler at night. Heat penetrating into the 40 building on the sedum portion of the roof was consistently greater than the herbaceous section during 41 the afternoon. However, during the night and early morning, heat gain into the building was greater on 42 the herbaceous roof, especially on cloudy and rainy days. During winter, heat transfer through the 43 sedum portion of the roof was affected more by outside environmental conditions, whereas the 44 herbaceous portion of the roof was stable. Although, the sedum roof exhibited more extremes, when 45 daily heat flux values were totaled for each month and each season, the herbaceous roof actually 46 3 experienced more heat entering the building during the summer, but less heat escaping the building 47 during the winter. This is an advantage during the winter months as the herbaceous roof would reduce 48 heating costs. However, contrary to conventional logic that plants with high transpiration rates are 49 superior, during the summer months the sedum roof outperformed the herbaceous roof. 50 51

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Although numerous examples of green roofs can be found in Turkey, limited research has been conducted on plant material and substrate type in this climate. Both plants and substrate are very important components in green roof design, it is essential to determine the proper substrates and plants in green roof systems for domestic green roof design. Two types of growing substrates: a commercial substrate consisting of crushed brick and clay (45%), pumice (45%), and organic matter (10%), and a recycled substrate including 90% coarse pumice (10–20 mm) and municipal compost (10%), were tested in three depths of 4, 7 and 10 cm. Tested plant species included Achillea millefolium , Armeria maritima , Sedum acre and Sedum album . Overall, the commercial substrate performed better than the recycled pumice. In addition, deeper substrates promoted greater survival and growth for nearly all species tested. Either A. maritima or A. millefolium survived in the recycled pumice at any depth, whereas they did survive when grown in the commercial substrate in greater than 7 cm and 10 cm, respectively. They both likely would require supplemental irrigation to be acceptable for green roofs in Istanbul or locations with a similar climate. Both Sedum species survived in all substrate types and depths. Information gained can be utilized by green roof professionals in the Istanbul region and in other parts of the world with a similar climate.

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