Existing structure and size, access and nearby vegetation

Existing structure and size

  • Consider the quality of the roof or vertical surface. Is it currently waterproofed? Does the wall have a surface that needs protection from vegetation?
  • Assess the area available – bearing in mind that costs increase with size. The useable area can be diminished if there are many windows on a wall or numerous vents and equipment on a roof.
  • Roof slope – green roofs are ideal on slopes less than 15 degrees but can be constructed on steeper slopes with special materials.
  • Water collection and storage opportunities – is there space to store water on-site? Tanks are usually located at ground level or in the basement of a building, and an irrigation tank may be co-located or shared with tanks for toilet flushing. Water storage can also be built into the design of some green wall systems.

Access

Good access is needed to deliver materials safely onto a green roof during its construction. Ease of access to the site will greatly influence the cost of instation

Good access is needed to deliver materials safely onto a green roof during its construction. Ease of access to the site will greatly influence the cost of instation

Evaluation of the site should review accessibility. Temporary access will be needed for machinery, and delivery and storage of materials during construction. For green roofs or multi-storey wall and facade greening, this might involve a crane to lift materials onto the site.

Consider how people will access the installation for maintenance, viewing or standing on.  This might require stairs, lifts and viewing platforms for the general public or building tenants. It may also require balustrades, cables for attaching harnesses and ropes (fixed fall protection), ladders, elevated work platforms independent of the building, or swing stages mounted on the top of the building for maintenance personnel. Access for maintenance to walls and facades can also be considered from below, in which case space for a temporary elevated work platform is likely to be required.  Further information about site safety is here.

Access for passers-by must also be considered, as there are regulations against vegetation that protrudes onto public space, and even in the private realm it is important to be aware of hazards that can be created for people using the space nearby.

Nearby vegetation

The local vegetation adjoining a site can influence design. If creation of habitat for biodiversity is a desired outcome for your green roof, wall or facade, consideration of the surrounding landscape could be useful. However, nearby vegetation can also be a source of weeds or contribute to a fire risk and should be included in site analysis.