Green Roofs
Overview
Green roofs are a popular option for reasons of aesthetics, sustainability and drainage performance. The growing medium takes the place of the traditional gravel or paving slab ballast typically found on inverted warm flat roofs.
Not only do green roofs provide much-needed greenery and habitat diversity in urban areas, the growing medium also acts as a buffer during periods of heavy rain. Rather than the water flowing straight off the roof and potentially overwhelming the drainage system, it is ‘stored’ on the roof temporarily, draining gradually to release the storm water at a more manageable rate.
How are different types of green roof classified?
The extra elements associated with green roof construction typically sit above a standard inverted roof build-up. Extruded polystyrene (XPS) therefore remains the preferred insulation option for either scenario. The exact nature of those extra elements depends on the type of green roof required.
Intensive: a fully accessible rooftop garden and amenity space. Requires irrigation, a relatively deep layer of growing medium, and a regular programme of maintenance.
Semi-intensive: somewhere between intensive and extensive roofs, and can incorporate elements of both, as well as featuring a greater range of planting.
Extensive: features a thin layer of growing medium (such as sedum mats), and is generally lighter and requires less maintenance than an intensive or semi-intensive roof. Irrigation is not normally required once established.
Biodiverse: similar to an extensive roof, but designed specifically to attract bird and insect life, using plants that create a specific habitat. A biodiverse green roof is seen as more effective than a brown roof.
Product Benefits
The Polyfoam range is lightweight, strong, moisture resistant and easy to cut and shape, providing thermal performance and strength for the lifetime of the building.
- 15mm lap joint.
- Excellent thermal performance.
- High compressive strength.
- Highly resistant to water absorption.
- Able to resist repeated freeze/thaw cycles.
- Lightweight and easy to install.
- Tough and durable, not easily damaged.
- Dimensionally stable.
- Thermal performance of an inverted roof is improved when used in conjunction with Polyfoam Slimline Zero Membrane.
- Environmental product declaration (EPD).
- BES 6001: Responsible Sourcing of Construction Products.
- ISO 9001, 14001, 45001 and 50001 management systems.
What Polyfoam XPS products are suitable for a green roof?
Whether a relatively simple green roof, or a roof garden designed for pedestrian access, Polyfoam Roofboard Extra can be specified as part of a durable, high performance build-up. The Polyfoam roof system will continue to provide performance even if subject to increased water volumes as part of a blue roof design.
An important part of flat roof design is the detailing and construction of suitable upstands around the roof edge, and Polyfoam Upstand Board limits heat loss due to thermal bridging at the junction of the flat roof with the external wall.