Structure

Extensive green roofs, also named as Eco-roofs, are characterized by their low weight, low capital cost and minimal maintenance nature.

Intensive green roofs, also named as Podium Gardens or Sky Garden, are characterized by greater weight, higher capital costs and maintenance requirements and more plant choice. It is geared for recreational use by human beings.

In Hong Kong Intensive Green Roofs are already well-established in the form of podium gardens. Extensive Green Roofs, on the other hand, are better-suited to retro-fitting projects which have their own technical constraints, and are not yet well-established in Hong Kong.

The table below shows the comparsion between extensive and intensive green roof systems.

Extensive

Intensive

Details

Soil thickness

50-150mm thick (thin soil)

200-2000mm thick (deep soil)

Irrigation

Little/ No required

Required

Maintenance

Low Maintenance

High Maintenance

Characteristics

Extensive application over large area

Intensive capital and maintenance input for optimal benefits

Advantage

1. Lightweight (80kg/m2-150kg/m2)
2. Low maintenance
3. Suitable for retrofit projects
4. Relatively inexpensive
5. Suitable for large areas
6. Suitable for root with slope 0-30o
7. Vegetation develop spontaneously

1. Diverse utilization of roof
2. Greater diversity of plants and habitats
3. Greater insulation properties
4. Simulate a wildlife garden
5. Attractive
6. Visually accessible

Disadvantage

1. Limited of plant choices
2. No access for recreation or other uses

1. Higher cost
2. Not suitable for green roof retrofit projects
3. Greater weight loading
4. Greater needs of energy. Water and materials resources