Green Roofs

Green roofs have enjoyed a surge in popularity over the last decade due to increasing recognition of the benefits that they can provide, These benefits include:

• Stormwater management. Helping to prevent drains from flooding
• Protect the underlying waterproofing system from ultra violet (UV) light
• Allowing buildings to blend in with the surrounding area – particularly in rural locations.
• Biodiversity. Providing a habitat for plant species, beneficial insects, etc…
• Helping to keep buildings cool in summer and warm in winter
• Mitigation of urban heat island effect
• Aesthetics – a green roof can be more attractive to look at than an asphalt-covered roof.
• Providing secluded green space in urban settings

Types of Green Roof

A wide variety of terms are used to describe different types of green roof, for example intensive, extensive, brown, and biodiverse. However the most fundamental division is between the pitched green roofs that evolved in Scandinavia and the flat green roofs that evolved in other parts of the world.

Pitched Green Roofs (Scandinavian-Style)

In parts Scandinavia pitched (sloping) green roofs (also known as turf roofs or sod roofs) are a common sight – particularly on traditional log buildings. Historically, they would have been constructed using birch bark to provide a basic waterproofing layer. In more recent times, dimpled cavity drainage membranes such as Oldroyd Xv Green together with bitumen roofing felts have been used instead.

Oldroyd Xv Green was specially developed in Norway for use on Scandinavian-style pitched green roofs. It benefits from a high recycled plastic content (>49%) and a rubberised surface to reduce slip-risk.

Oldroyd Xv Green is laid on top of a suitable exterior grade bitumen roofing felt and fixed into place using Oldroyd Turf Roof Plugs. An edge-detail is formed using treated timber and Oldroyd Turf Roof Hooks. The turf or sedum layer is then laid directly onto the Oldroyd Xv Green.

A basic guide to constructing this type of pitched green roof can be downloaded from this page.

Flat Green Roofs

Flat green roofs (actually they usually have a pitch of up to 10 degrees to prevent pooling of water) come in a wide variety of shapes and sizes. Flat green roofs can broadly be divided into two categories:

• Extensive Green Roofs – These have a thin layer of vegetation and low soil depth to minimise weight. Sedum is a popular type of vegetation for this type of green roof.
• Intensive Green Roofs – These have a deep soil layer and are capable of supporting more plant species than extensive green roofs. However their weight means that a strong structure is required to support them.

The typical layer build up is actually very similar for both types of flat green roof.

The Safeguard Root Barrier is necessary to prevent root damage to the waterproofing layer. However it may be omitted if the waterproofing layer has adequate integral root resistance properties.

The Oldroyd Xv 20 GreenXtra drainage layer allows excess water to be drained away in times of heavy rainfall. However, it also stores water in 'cups' to provide moisture to the growing layer in times of low rainfall.

The Oldroyd Tp filter fleece prevents fines from the growing medium from passing through into the drainage layer and causing blockages.

Green Roof Kit

Large-scale flat green roofs require specialist skills to install. However, installing an small extensive green roof (for example on an extension that has an unattractive asphalt roof) is a job that could be undertaken by someone with good DIY skills. A green roof kit is available for small projects up to 9 m².