THE MAGIC OF GREEN ROOFS
Green roofs provide a great way of turning unused space into living habitats. This can provide entertainment and enjoyment for all.
Alongside this, there are many practical benefits to installing a green roof. These include flood management, reduction of dust or smog levels. Also provision of an acoustic barrier, improvement of temperature regulation through the seasons. Lastly it ensures urban buildings look more attractive. While rural buildings suit their surroundings. This as well offers an environment where wildlife can thrive. It can also help to extend the life of the roof by providing added protection to its waterproofing.
Green roofs are typically made up of a series of basic layers. This comprises a waterproof membrane, a root barrier, a drainage layer such as lightweight composite or preformed plastic cellular layers. This prevents water logging and stress to the structure due to the weight increase as a result of excess water. Also a filter mat between the drainage layer and soil to stop the drains clogging, followed by the plants. All this must sit above the roof structure and insulation.
Green roof systems are required to have a minimum dry weight of 80 kg/m2. This is to ballast the insulation beneath them if the insulation is not to be mechanically fixed down. This is to prevent uplift as a result of bad weather conditions. However, the total required dry weight will vary with the geographical location of the building. Local topography, and the height and width of the roof will also need to be considered. The necessity for any additional dry weight should be assessed in accordance with BS EN 1991-1-1:2002 (Densities, self-weight, imposed loads for buildings). BS EN 1991-1-4:2005+A1:2010 Eurocode 1 (Actions on structures, general actions, wind actions) is an alternative.
Insulating green roofs
The recommended insulation materials for both intensive and extensive green roof systems are those which can demonstrate a combination. This includes compressive strength, low weight, ease of installation, and long-term thermal performance.
PIR insulation such as the Thermataper range from Kingspan Insulation can offer durability as well as being lightweight. This helps reduce the design load. This is suitable for extensive and semi-intensive green roofs. For heavy intensive green roofs incorporating larger shrubs and trees with a soil depth of 300 mm. Kingspan Styrozone is the recommended insulation product.
Kingspan Styrozone is a high performance, rigid extruded polystyrene board with high compressive strength. It is available in a number of different grades and sizes to suit project requirements.
Types of green roof
Extensive green roofs are constructed using low-growing, resilient plants, for instance stonecrops (Sedum), grasses, and herbs. This can greatly improve the building’s aesthetics and biodiversity. The plant species chosen are intended to be hardy and low maintenance. However these roofs are often unsuitable for recreational use.
Intensive green roofs are designed as simple gardens or fully landscaped leisure spaces. These can support plants ranging from grasses to trees. As with extensive roofs, they have environmental, ecological, and economical benefits, and can also provide useable outdoor areas. Unlike extensive roofs, these spaces are high maintenance and the increased structural loading could also pose a problem. Especially if the extra weight of deeper substrate and larger plants are not effectively accommodated. Structural loading should be considered as a priority during specification, particularly if retro-fitting.
Further guidance on Kingspan products that are suitable for green roof applications are found here: