Flat Green Roofs

Knowledge of green roof construction methods and the benefits of incorporating them in building design is steadily becoming more widespread in the UK.

Unlike pitched green roofs, flat green roofs can either take the form of extensive (consisting of a thin layer of turf or sedum matting), or intensive (characterised by a greater soil depth that can even accommodate shrubs and trees). This more frequently takes the form of roof-top gardens, providing valuable secluded green space in urban settings.

Flat green roof build up

The build-up of a flat green roof will vary depending upon the intended use. We therefore suggest that you contact our technical department early on in the design process. However the diagram below shows a typical build-up for an extensive or semi-intensive green roof:

A standard roofing membrane and insulation layer is laid onto the underlying roof structure, then a studded, perforated drainage membrane such as Oldroyd Xv20 GreenXtra is used in addition to provide a drainage layer with reservoir capability. A filtrating drainage layer (Oldroyd Tp filter fleece) is laid down before adding the required soil loading and plantings, as shown in the diagram above.

For roof-top gardens, concrete decking is often used to provide a suitable load-bearing construction, whereas substantial reinforcement is not usually required for a lightweight flat turf roof.

Biodiverse Roofs

Biodiverse roofs are flat green roofs which have been specifically designed with particular biodiversity objectives in mind - see our biodiverse roofs page for details.

Fixing Guide

A guide to installing flat green roofs can be downloaded free of charge in PDF format by clicking on the image to the left.

The guide shows how Oldroyd Xv20 Green Xtra can be used in conjunction with a primary waterproofing system to create a flat green roof.