The first step in considering a green roof for an existing building is to have its structural loading capacity assessed by a structural engineer. With this figure, which must include both live and dead loads, you can then decide what kind of green roof system the roof will support.
Depending on the system used, extensive green roofs weigh between 60 and 240 kg/ m2 (Kolb & Schwarz, 1999). If you wish to retrofit a ballast roof, the weight of the ballast may match the loading required for an extensive green roof. The structural engineer will provide you with this important information. For details about regionally-available green roof systems, components, and/ or services, visit our industry products page.
Kolb, W. and T. Schwarz. 1999. Dachbegrünung: Intensiv und extensive. Eugen Ulmer, Stuttgart.