Green Roofing 101: Green Roof Terminology

by Greg Garner, President of Elevated Landscape Technologies, Inc.

As mentioned in my last article, green roofing is the integration of two different disciplines, roofing and landscaping. As a result there may be unfamiliar terminology. Here, we will go through some of the more common terms with brief explanations of each.

Intensive green roof - A type of gree roof involving more elaborate designs and plantings usually with deeper depths of growth medium, larger vegetation and possibly more hard scaping. Also referred to as a "roof top garden".

Extensive green roof - A type of green roof providing a vegetative covering in a manner minimizing inputs. Provides all of the environmental benefits in the most cost effective maner possible. Shallower depths of growth medium, lighterweight as well as having more limitations with regards to plant selections are the main characteristics of this system.

Pre-vegetated - Describes a green roof system where the vegetation is established into the panel, mat or tray at a nursery prior to delivery to be installed as a one step, complete green roof system.

Plant-in-place - Describes a green roof system where the installation process is to install the necessary components seperately and establish the vegetation on site over a period of time. Vegetation may be propagated from plugs, pots, or in some cases seed.

Growth medium - Medium consisting of organic and inorganic components like in soil; only it is not soil. Soil is found at ground level and occurs as part of a naturural eco-system. Green roof growth mediums are engineered to meet specific performance specifications and are produced or blended using components that have characteristics that promote drainage, are light weight, and will sustain vegetation with little inputs.

Organic matter - Material from once living plant material that has expired and is in a stage of decompisition providing nutrients, water retention, and beneficial micro organisims activity. Compost is a common source of organic matter used in green roof growth mediums.

Inorganic material - Material that is mineral base. Various aggregates like pumice (volcanic rock), expanded shale, expanded clay, sand, and others can be used to provided drainage, aeration and growth medium structure.

Root barriers - a component or layer of a green roof system to prevent root penetration into the water proof membrane.

Drainage board - a component of a green roof system that allows excess water from rain events to move underneath the growth medim/vegetation and exit the roof via the roof drains.

Filter fabric - A layer of material that prevents growth medim from eroding down through the drainage board or through retaining walls from a rain event.

Vegetation Carrier - a component that performs as a drainage board, filterfabric, irrigation system, and root anchoring system for the vegetation.

Vegetation Free Zone - Usually and area around the perimeter of the roof or around a drain that is not to have vegetation growing there. Quite often river rock or round stone is used to facilitate this feature.

These are not all of the commonly used terms but is a good start to speaking the green roof language.

Greg Garner has been installing roof membranes and green roof systems for over seven years and has over 15 combined years in the landscaping and roofing contracting businesses. Greg also has invented and commercialized several patent pending technologies currently being used in the green roof and living wall industries - ELT EasyGreen