What are green roofs, walls and facades?
Vegetation on green roofs is planted in a growing substrate that can range from 50mm to over 1 metre in depth, depending on the weight-bearing capacity of the building’s roof and the design objectives.A green roof is a vegetated landscape that is installed on a roof surface, and is built up from a series of either loose-laid layers, or modules made of pre-prepared layers in trays.
Green facades are created by growing plants up and across the face of a building.
Plants are either rooted in the ground or grown from containers installed at different levels on the face of the building.
Climbing plants can attach directly to the surface of a building or be supported on a structure independent of the building.
Green walls are plants grown in vertical systems that are usually attached to internal or external walls.
Green walls differ from green facades in that plantings are made across the entire vertical structure, as opposed to planting at the base of the structure to enable vertical and horizontal growth.
In a green wall, plants, growing medium, irrigation and drainage are incorporated into the system.
What are the benefits of green roofs, walls and facades?
A well designed and maintained green roof, wall or facade can provide:
- Aesthetic improvements in highly visible locations;
- Protection of building materials leading to an increased lifespan of those materials;
- Reduced building heating and cooling costs due to increased insulation;
- Green spaces (and sometimes usable recreation spaces) in densely built environments;
- Increased property value;
- Food production areas for residents or commercial tenants;
- Rain water run-off management and water filtering/pollution reduction;
- Habitat creation and increased biodiversity;
- Cooling effect for the city – where there is a high density of green roofs, walls, facades and other types of greenery such as street trees;
- Cleaner air, with less pollutants.
The Three Key Areas of Development
Well considered design is vital to realise the potential benefits of a green roof, wall or facade installation.
If a green roof is intended to increase the permeable surface on a site, and to decrease stormwater run-off, a deep layer of growing substrate should be used.
Design considerations also include understanding the site’s aspect and exposure so that suitable plants are selected.
One of the most important design considerations lies in understanding the structural load that the wall or roof can take to determine what can be installed.
If structural capacity is limited it may be possible to reinforce the walls or roofs to increase the weight loading capacity.
Design must also take into account the project budget and a realistic assessment of the resources available for ongoing maintenance.
For shallower designed green roofs, also known as extensive green roofs, the benefits of reduced stormwater run off is less in comparison to the deeper intensive green roofs.
Roofs, walls and facades can be installed on existing buildings, or built into new structures.
In new builds it is important that the green roof, wall or facade installer is involved in discussions with the project team during the design phase, and not just brought in later to work around the existing conditions.
Care must be taken where multiple contractors are involved in an installation that no damage is made to earlier work, for instance to the water proofing membrane, and that warranties and insurance liabilities are clear.
Access for builders can be difficult and consideration must be given to OH&S requirements for working at heights.
Irrigation systems are usually incorporated into green roof, wall and facade installations, and thought should be given to water collection and storage, and in some cases water re-use through the system.
Maintenance is critical to the success of a green roof, wall or facade.
Maintenance will depend on:
- Irrigation in particular must be maintained to ensure proper operation;
- The vigour of the vegetation;
- Use of the roof or facade (e.g. if growing food versus creating a biodiversity space);
- Aesthetic preferences for the roof, wall or facade;
- Number of likely weed seed sources around the site.
Design Goals and Considerations
The following tables provide some examples of different considerations for different design goals.
This is not an exhaustive list, and is intended only to illustrate that different goals will require different inputs and system set ups.
Discussions with professional green roof, wall and facade installers, landscape architects, structural engineers and a review of relevant research will be needed to make final decisions about the most appropriate approach.