What are they?
Green roofs are a specifically designed planting system to provide a habitat for wildlife, enhance ecological value and aesthetic appeal and reduce heat gain / loss from the building. Green roofs take a variety of forms and can be categorised as either ‘extensive’, ‘intensive’ or ‘semi-intensive’.
- An extensive green roof is characterised by moss, herbs and grasses and is primarily used as an ecological landscape.
- An intensive roof is more managed and can be used as a garden with a lawn and perennials, shrubs and trees and can be incorporated with amenity space for tenants.
- A semi-intensive roof is a mixture of extensive and intensive types.
‘Brown’ roofs are similar to green roofs. The main difference is the choice of growing medium (usually locally sourced rubble, gravel, etc) to meet a specific biodiversity objective. They are generally less attractive than green roofs but equally valuable in terms of biodiversity.
A living wall is a living and self-regenerating, cladding system using climbing plants.
Advantages / Disadvantages
Increases biodiversity on the building / site making a positive sustainability statement. Can have effective insulation properties to prevent heat loss in winter and provide passive cooling in summer.
Intensive roofs can be used as an amenity space.
Potentially high maintenance depending on the planting strategy adopted.
Irrigation is a key consideration, particularly if there is no rain or grey water recycling in place or there is planting present that has as a high water dependency.
An existing roof may not be able to support the additional structural load of a green roof without strengthening works being undertaken, which may be impractical.
Care is required to ensure that the green roof does not compromise the water tightness of the roof.
Running costs
Intensive green roofs and living walls will have higher running costs compared to extensive green roofs or brown roofs due to higher maintenance requirements and water consumption.
A rainwater harvesting or grey water recycling system for irrigation purposes will reduce mains water consumption.
Green roofs can also reduce a building’s energy demand by preventing solar gain and providing insulation thereby saving both energy and running costs.
Retrofit / improvement opportunities
Straightforward to retrofit providing there is adequate free roof space with easy access, no shading and the existing roof can accommodate the additional load. If the existing roof structure cannot take the additional load of a green roof then strengthening works will be required.
Retrofitting a green roof should take into consideration the future space required for the tenant to install additional plant and equipment on the roof (e.g. air conditioning units and air handling units).
Living walls generally require supporting structures which will in turn require planning permission.
Applicable buildings
All building types can benefit from green or brown roofs or living walls. However, multiple design issues, such as drainage, irrigation, access for maintenance, additional structural load, shading and aesthetic appeal, need to be considered.
Floor plate implications
None.
Occupant comfort
Intensive green roofs in the form of terraces can provide good views and an amenity space for occupants providing appropriate maintenance and irrigation is applied to avoid deterioration in appearance. Planting can include edible plants such as herbs that tenants can use.
Maintenance implications
Extensive green and brown roofs will require annual maintenance whereas intensive roofs and living walls will require regular attendance and management. Typically, a biodiversity management plan will be in place which will set out specific maintenance actions and frequency.
Identification
Green roofs will feature a range of planting types of various sizes and become established over time. Brown roofs may have rubble or other hard materials on them to encourage colonisation by fauna as well as flora.
Living walls comprise an area of the building façade featuring climbing plants set on a dedicated frame and with an irrigation system.
Questions to ask
- Is there a green roof, brown roof or living wall on the building?
- Is the green roof extensive or intensive?
- Where is the water for the feature sourced?
- Is there a biodiversity management plan for the feature?
- What is the maintenance cost and does it add to the service charge?
More information
References required
