Basically there are two different types of green roof systems, either intensive or extensive
Intensive and Extensive
Basically there are two different types of green roof systems, either intensive or extensive. You will know the two types by their structures. An intensive roof normally requires a very massive structure to support it. If for example we wanted to have trees growing on top of our roof, it would be necessary to provide soil approximately three feet deep to sustain the desired vegetation. As you can imagine when that soil is wet, it will present a massive dead load on the structure. You will typically find an intensive system on parking decks, massive structures, and things like that where you have the structural capacity to support that kind of load. An extensive green roof system on the other hand is a very lightweight system that will impose a minimal dead load on the structure of the building. Typically with an extensive roof system, the entire area of the roof is green. The final roof covering is intended to make the entire roof appear like a meadow or field in a natural state. There are a variety of different elements involved in extensive and intensive roof systems. Each one of these roof systems will consist of a structural deck with insulation to comply with local energy codes on top of that. One questions often asked is; will the green roof itself add r-value to the roof system and to the building? The answer is yes; but only at certain times of the year. We are going to try to keep these roofs moist and anything that is wet becomes a thermal conductor, not an insulator. When you are calculating the r-value for a roof you should not include any additional r-value that will be generated by a green roof system. Always include the amount of insulation that will necessary to give the proper r-value required for the building.