Case studies 6 min read
The load budget of a green roof: a worked example
When the slab has only 180 kg/m² to spare, the drainage layer decides the whole build-up.
In a roof refurbishment on an office complex, the structural check found only 180 kg/m² of spare capacity — to be divided between drainage layer, growing medium, planting and saturation water.
A 100 mm gravel drainage course weighs around 190 kg/m² saturated. On its own it went straight past the entire budget.
The same depth in 8–16 mm expanded clay weighs about 65 kg/m². What was left over allowed the growing medium to go from 120 mm to 200 mm deep, and the planting scheme to move from ground cover up to shrubs.