Type III


CSI Specification: Type III (DOCX)   -----------------
CSI Specification: Type III (PDF)

The dual media Type III assembly utilizes a granular mineral drainage media layer beneath a lightweight, fine-grained growth media. A root-permeable separation fabric separates the media layers and keeps the growth media fines from mixing with the granular media. The permeable granular media base provides several advantages; it 1) absorbs moisture, 2) provides additional hospitable volume for root growth, and 3) moderates the rate at which water is discharged from the green roof. This assembly best approximates the natural conditions associated with shallow soil over shale bedrock. Assembly thicknesses typically range from 4 to 8 inches (10 to 20 cm). Compared to Type II assemblies of a comparable thickness, Type III assemblies are significantly more drought tolerant and accommodate a broader plant palette, even supporting turf in many climates. Type III green roofs promote strong plant growth by draining and distributing water efficiently and concentrating root mass in a stable temperature and moisture zone. If irrigation is required, then highly efficient base capillary irrigation introduces water at the root level, an approach that minimizes water loss from evaporation and promotes deep root development.

Typical Type III profile:

  • wind erosion stabilization system
  • growth medium
  • root-permeable separation fabric
  • light-weight granular drainage media
  • protection fabric (for un-irrigated systems)
  • capillary fabric (for irrigated systems)
  • root barrier membrane (when required)
  • waterproofing system

Data Sheet

Type III Data Sheet

Case Studies

Heinz 57 Center, Corporate Headquarters, Pittsburgh, PA
Pacific Plaza, Tacoma, WA
University of Pennsylvania, Fagin Hall, Philadelphia, PA