Water retention capabilities, weight implications?
On a year-round average, 55%-80% of all storm water that falls on a roof garden is retained and not released into the drains. All weights reported in roof garden assemblies reflect the saturated weight. As an example, if a growth media weighs 35 pounds per cubic foot dry and 60 pounds per cubic foot saturated, a 12″ deep garden would hold up to 25 pounds of water per square foot. This is equivalent to 3 gallons of water or 4.8″ of rainfall. Building owners should consult a structural engineer to ensure that the structure is capable of sustaining the additional load of a saturated Roof Garden.
