We will be designing a vegetative extensive green roof on the very top of the B-home structure.

Soil: Much lighter than intensive green roofs. Soil depth is 1-6 inches and weight load 15 – 50 pounds per square foot.

Most current experts frown on using topsoil at all for fear of introducing unwanted properties. Generally, if you are mixing your own substrate, a good guideline is approximately 75-80% inorganic (i.e., expanded slate or crushed clay) to 20-25% organic (humus + some clean topsoil). This will provide essential drainage and soil air capacity, and sufficient organic nutrients for the shallow-rooted plants. Just remember that your weight requirements will be higher with a greater concentration of topsoil, and weeds and certain pathogens are always possible when ordinary garden topsoil is added.