Getting it right through design

There are fundamental principals that apply to the design of a green roof, regardless of the proposed landscaping, location or climate. The specified solution must replicate nature within the build up and be able to support the vegetation.

The first step - What is the landscaping finish to look like?

The primary decision is the type of landscape required that best suits the rationale behind the development, whether it is an intensive, simple intensive, extensive or biodiversity roof. Whatever the landscape chosen, the plants will have some basic requirements to sustain them; nutrients, a balance between moisture and drainage to suit the vegetation, and aeration to the root systems.

The next step - Planning the green roof to meet the needs of the vegetation

Once the vegetation finish has been determined the structural and design considerations and green roof components can be proposed.

Waterproofing system, structural loading and wind uplift

The structural design of the building will embrace the specification of the appropriate waterproofing system to meet the demands placed on it by the green roof and the effects of climate, especially with regard to performance against high-wind. More ►

Falls and drainage

How a green roof holds water for the vegetation whilst also allowing for appropriate levels of drainage is important when looking to reduce levels of rainwater run-off.  More ►

Configuration of green roof components 

The selection of components to balance water storage and drainage of excess rainwater is, to a certain extent, dictated by the vegetation finish selected for the green roof.  Insufficent water storage means that either additional irrigation may be required or the vegetation will struggle to flourish.  More ►

Perimeters and vegetation barriers

Perimeter details have minimum requirements to comply with building regulations and vegetation barriers have important functions, one of them being to act as a fire break.  More ►

Irrigation, maintenance and safe access

Every green roof will require access for maintenance and in the case of intensive green roofs access is continual.  All access on green roofs should be safe for the user.  More ►

Designing to protect the building's construction and flat roof waterproofing is vital when delivering a green roof as many additional forces can affect the structure.  Green roofs are installed on roof pitches ranging from 1° to around 30°. Fundamentally it’s about finding the balance between requirements for water storage, drainage and irrigation; sufficient depth of growing medium to support the intended vegetation and weight loading levels; as well as meeting the regulatory needs for construction, fire, safe access and the duty for maintenance.

Codes of practice 

To date there are no British Standards to guide Specifiers, Contractors, and their clients as to the best method to achieve this. At present the most widely accepted standard amongst the leading green roof suppliers in the UK, is the German FLL standards.

The Green Roof Organisation (GRO) is a partnership of Industry and Stakeholders coming together to develop guidance for specification, design, manufacturing, installation and maintenance of Green Roofs.  You candownload the GRO Code of Practice 2014 here ►