Deeper layer of growing medium; irrigation system; more favorable conditions for plants; high plant diversity; often accessible.
• Greater diversity of plants and habitats.
• Better insulation properties.
• Can simulate a wildlife garden on the ground.
• Can be made very attractive visually.
• Often accessible, with more diverse utilization of the roof. i.e. for recreation, growing food, as open space.
• Greater energy effi ciency
• Larger storm water retention capability.
• Longer membrane life span
• Higher need for irrigation and drainage systems requiring energy, water, materials.
• Higher capital & maintenance costs.
• More complex systems and expertise.
Thin layer of growing medium; little or no irrigation; stressful conditions for plants; low plant diversity.
• Lightweight; roof generally does not require reinforcement.
• Suitable for large areas.
• Appropriate for roofs with 0 - 30° (slope).
• Low maintenance and long life span.
• Often little need for irrigation and specialized drainage systems.
• Less technical expertise needed.
• Often suitable for retrofit projects.
• Can leave vegetation to grow spontaneously.
• Relatively inexpensive.
• Looks more natural.
• Easier for planning authority to demand as a condition of planning approvals.
• Less energy efficiency
• Less storm water retention benefits.
• More limited choice of plants.
• Usually no access for recreation or other uses.
• Unattractive to some, especially in winter.