Type II


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

Type II assemblies include a synthetic drain layer that offers a much lower resistance to water flow than growth media. In this assembly, the drainage layer is a geocomposite sheet drain, and the growth media exhibits a moderate permeability and porosity. A filter fabric separates the media from the underlying geocomposite sheet drain. The root-permeable filter fabric keeps media fines out of the drainage zone. A common variation, used mostly in conjuncton with PMR roofing systems, utilizes a sheet drain with recesses to retain water. This type of sheet minimizes the loss of moisture into the underlying insulation. To reduce plant stress during drought conditions, the drainage layer should not exceed one-inch (2.5 cm) in thickness. Type II assemblies are probably the most common extensive assemblies in the United States, and typical assembly thicknesses range from 3 to 6 inches (8 to 15 cm). This assembly is not optimized for irrigation, which is not recommended in temperate climates.

Typical Type II profile:

  • wind erosion stabilization system
  • growth/drainage medium
  • root-permeable separation fabric
  • sheet drain
  • slope stabilization system (for roofs pitches exceeding 2:12)
  • protection layer
  • root barrier membrane (when required)
  • waterproofing system

Data Sheet

Type II Data Sheet

Case Studies

WGBH, Boston, MA
Testa Produce, Chicago, IL