For a green roof to flourish it requires suitable amounts of sunlight, water, sufficient drainage and aeration to encourage healthy plant growth. To deliver a successful green roof the designer must consider the building's position and location, along with the orientation of the roof during the day and any shade from surrounding buildings. The roof's height can have an affect due to wind action, and can cause wind scour of the substrate. Pebble borders are generally used to avoid this.
The additional weight loading from a green roof is a major factor to consider as the structure must have sufficient load bearing capacity to support a water saturated green roof system. The roof must have sufficient drainage which will help reduce the imposed loads and prevent excessive saturation of the growing substrate which can lead to deterioration of the planting.
A green roof will require regular safe access for maintenance and it is important that adequate fall protection measures are put in place to allow for safe inspection and maintenance of the roof.
The waterproofing system is paramount to the success of the green roof, as it is fundamental to prevent water ingress into the building. Many BMI waterproofing systems are suitable for use beneath a green roof and it is essential, when designing the roof details, that all adjacent building elements and interfaces are considered.
Green roofs will require water and provision for irrigation should be considered at the planning stage. All Green roofs will require irrigation during the establishment period and so a temporary water source should be provided. Intensive roof planting and lawns will require a permanent irrigation system to keep them supplied with water during hotter, drier, summer months. Extensive roofs will only need irrigating during the establishment phase, and very little subsequently except during longer periods of drought. Pitched roofs retain less water and therefore a permanent irrigation system should be considered.