Broadly speaking, a green roof is one with plants growing on its surface. This could range from a spontaneously occurring moss and lichen covered roof to a full-scale roof garden that includes trees, shrubs and hard landscaping features. The practice of roof planting in Europe is at its most technically advanced in Germany where green roofs have been fundamentally divided into two categories, intensive and extensive.

Intensive green roofs are roof gardens and like any garden provide space for people. They require the intensive management of a ground level garden, are usually based upon a thick soil or substrate layer and require artificial irrigation. Preferred plants are selected and the roof conditions created to support them. They are heavy systems and thus can have major structural implications for the building.

Extensive green roofs are not usually recreational (although extensive planting can be integrated with intensive systems). They have low management requirements and do not usually require artificial irrigation. Plants are selected that will succeed with only minimal modification of the normal roof conditions. Planting styles are usually naturalistic with the objective of establishing a self-sustaining plant community on the roof. Based on a thin layer of soils or substrates, they are lightweight systems with minimal structural implications for the building. The main reasons for installing an extensive green roof are visual appeal, reducing the environmental impact of the building, creating habitat for native flora and fauna, and enhancing building performance.

BHC can cater for both types of roof planting; however, our prime service is in the design, supply, installation and maintenance of extensive type roof planting systems.

Extensive green roofs can be subdivided into a range of different systems dependent upon the composition and depth of the substrate and on the plant species used. The essential benefits of extensive green roofs are the following:

• Visually attractive with a range of flower and foliage effects.
• Low maintenance with little or no artificial irrigation requirement.
• Improved rainwater management. Volume and rate of rainwater run off from the roof is reduced dramatically.
• Improved building thermal performance. The building is insulated from heat loss in the winter and heat gain in the summer.
• Reduction in sound transmission through the roof.
• Improvement of air quality by removal of carbon dioxide, release of oxygen and water vapour, deposition of particulate pollutants, and absorption of organic volatiles.
• Reduction of the 'urban heat island effect'.
  
• Provision of habitat for wildlife.

The prime objectives in the design and construction of a system is that the established planted roof will be aesthetically pleasing, environmentally beneficial and will not compromise the essential function of the roof, that is, to prevent water entering the building. The following criteria are taken into account:

Position of the building,orientation of the roof,height of the roof above ground, roof pitch, weight limitations of the building, preferred planting, sustainability of components, levels of maintenance, and performance required from the plant layer.

Generally, our systems are based on the following elements built up on the pre-installed waterproofing layer:

The plant layer can be installed using the following methods:

• Hydroplanting and seeding. Cuttings and seeds are spread on the prepared substrate and overmulched. This mulch is usually applied as a slurry with specialised equipment. The cuttings root and the seeds germinate to produce the plant cover.
  
  
• Plug and hydroplanting. Rooted young plants (plugs) together with hydroplanting as above are used to establish the plant cover.
  
  
• Nature Mat®. The plant material is grown to maturity in our fields in the form of a mat that can be rolled up,transported to the roof and laid on the prepared substrate to produce an instant green roof with a minimum of 90% plant cover. For more details, please see the main menu.

Design of our green roof systems is very much tied to our own experience, analysis of German systems and findings from our ongoing trials in this country. Our systems essentially have two components, the aesthetic and the functional. The former describes the nature of any visual appeal that is required. The latter refers to the important functional aspects of the planting which could include improved building performance, reduced environmental impact or habitat creation. A consultation process is used to determine the type of roof required and whether that can be achieved within the framework of structural limitations, prevailing environmental conditions and time scale. Once this has been determined we can combine relevant drainage, substrate and plant components and the appropriate methods of installation to create the desired result.

We also offer a similar consultative design process to meet your other landscaping needs, whether interior or exterior.

Roof greening requires plants that have been specifically chosen to withstand the harsh roof environment- drought conditions, frost, snow, sea winds and so on- and our horticultural experts who lead this field in the UK are able to offer a wide selection of plants which have been proven to withstand the worst effects of the British climate.

Sedums which are commonly known as Stonecrops are the core species for BHC green roof systems in the UK. They are a versatile and attractive ground cover plant belonging to the Crassulacaea family. Sedums are evergreen, self-generating, drought resistant and capable of withstanding extremes of climate. They flower from early summer through to autumn in shades of pink, purple, yellow and white. Needing very little attention and no mowing or cutting back, they give excellent foliage colour and texture and are attractive to all kinds of insects and birds. Sedums are generally pest and disease free but,like most plants, can suffer from aphids, mealy bugs, thrips or vine weevil which can be controlled by biological means.

Other succulents, grasses, herbaceous perennials and bulbs are also used depending on the project.

Young plug plants are available in a wide variety of species or can be grown to order. See price list.