types of green roof

Extensive:
Providing environmental and cost benefits these roofs are very low maintenance and aesthetically pleasing. Generally a shallow layer of substrate (25-100mm) planted with low-growing succulents called sedum, and occasionally wildflowers, herbs and other alpine species. The plants will give excellent coverage of the entire roof. Extensive roofs are not designed for access, but are ideal for both retro-fitting & new build of pitched roofs or flat roofs to provide insulation or water attenuation. These light-weight systems require only annual or six monthly maintenance, and do not impose any significant weight on the building structure; therefore there are usually no structural implications. A low cost long-term solution that does not require irrigation. The Extensive green roof is designed to be self-sustaining and to look ‘natural’.

Intensive:
Intensive gardens are based on a thick layer of soil or substrate (150mm+) These are roof gardens which are created to provide additional space for people to use as amenity; they usually have a flat roof or shallow pitch and can incorporate lawns and specially selected shrubs, trees and plants. Roof gardens require the same ‘intensive’ maintenance and upkeep as the ground level garden. Irrigation and drainage systems must be adequately designed. Pathways, terraces and other architectural features can be included. Intensive roof gardens place significant weight on the building structure and need to be engineered to conform to load requirements and health and safety. Visually they are very attractive but have high capital and maintenance costs.

Simple Intensive:
Of slightly greater depth than extensive systems (100-200mm), allowing a greater diversity of plants to be grown and local habitats recreated. Based on the same principles as extensive roofs, they are light weight and generally low maintenance. The planting usually covers the surface of the roof.

Brown or Rubble roofs
The by-products of the development process such as rubble, brick and subsoil are added to the roof and allowed to colonise naturally over time or planted with wildflower meadows. The concept behind such roofs is to replace the ‘foot print’ of the building on the roof thereby recreating ‘Brownfield’ conditions and providing a habitat to encourage the local species of plants, birds and invertebrates, displaced by development, to return and colonise the roof.
They consist of a lightweight growing medium, typically made up of crushed brick or concrete mixed with site excavated soil. This can be recycled material that has an association with the site; demolition material then left to colonize on its own. Similar results can be had by leaving a commercial substrate to colonize naturally Experience has shown that there is a need to seed and ALSO apply some sedums to such roofs to ensure that the roof develops to its maximum.The substrate will be free draining and has a low-fertility.
The finished surface is ‘sculpted’, to provide habitat for the specific flora and fauna it is designed to accommodate. Features such a logs and boulders are often added.