Green Roofs

Code: 
U01
Sector: 
Urban
The complete description of the NWRM: 
Summary: 

Green roofs are multi-layered systems that cover the roof of a building with vegetation and/or green landscaping over a drainage layer. There are two types of green roof:

  • Extensive green roofs cover the entire roof area with lightweight, low growing, self-sustaining, low maintenance planting. They are only accessed for maintenance. Vegetation normally consists of hardy, drought tolerant, succulents, herbs or grasses. Extensive green roofs are often known as sedum roofs, eco-roofs or living roofs.
  • Intensive green roofs are landscaped environments with high amenity benefits including accessible planters or trees and water features. These impose a greater load on the roof structure and require significant ongoing maintenance including irrigation, feeding and cutting. Intensive roofs are also termed roof gardens.

A typical structure for a green roof includes a surface vegetation layer underlain by a substrate (growth medium), geotextile filter layer, and an aggregate or geo-composite drainage layer. The green roof materials are underlain by a waterproof membrane, with an additional layer of insulation between that and the roof itself. Green roofs are designed to intercept rainfall, which is slowed as it flows through the vegetation and a drainage layer, mimicking the predevelopment state of the building footprint.

Some of the rainwater is stored in the drainage layer and taken up by the vegetation, with the remainder discharged from the roof in the normal way (via gutters and downpipes). Flow rates from the green roof are reduced and attenuated compared to a normal roof, and the total volumes discharged from the roof are also reduced. Green roofs therefore intercept rainfall at source and provide the first component of a SuDS management train.

Illustration(s): 

Green roof

Source: Andras Kis’ presentation, NWRM Workshop 1

Possible benefits with level: 
Benefits Levelsort descending
BP5 - Increase evapotranspiration High
ES3 - Natural biomass production Low
ES4 - Biodiversity preservation Low
ES9 - Filtration of pollutants Low
ES10 - Recreational opportunities Low
PO2 - Improving status of physico-chemical quality elements Low
PO4 - Improving chemical status and priority substances Low
PO7 - Prevent surface water status deterioration Low
PO14 - Prevention of biodiversity loss Low
BP8 - Reduce pollutant sources Low
BP14 - Create terrestrial habitats Low
BP16 - Reduce peak temperature Low
BP17 - Absorb and/or retain CO2 Low
BP9 - Intercept pollution pathways Low
ES5 - Climate change adaptation and mitigation Medium
ES7 - Flood risk reduction Medium
ES11 - Aesthetic/cultural value Medium
PO9 - Take adequate and co-ordinated measures to reduce flood risks Medium
PO11 - Better protection for ecosystems and more use of Green Infrastructure Medium
BP1 - Store runoff Medium
BP2 - Slow runoff Medium
Last updated: 09 Jun 2015 | Top