Green roofs are a favourable solution both from an ecological and a technical point of view. The permanent loads arising from the weight of the vegetation layer usually represent only a little additional load compared to the loads of a traditional terrace roof with normal paving slab or a gravel-ballasted flat roof. In return are the benefits offered by nature.
- reduced load on the rainwater drainage system
- considerable amount of bound particulate matter
- better heat balance on the roof
- excellent microclimate
- considerable carbon dioxide binding ability.
Inverted roofs make excellent green roofs, and XENERGY™ SLP is the ideal reliable thermal insulation material for this application.
For further guidance on Green Roofs: https://livingroofs.org/code-practice-green-roof-organisation/
ADVANTAGES OF GREEN ROOFS
Green roofs and roof gardens are becoming more and more important in urban environments, allowing some of the space occupied by the building return to green surface. Green roofs offer expanded living space, contribute to the clean air and also have a considerable rainwater-retaining effect. Green roofs also have an indirect beneficial effect by relieving the rainwater and wastewater sewerage networks. Inverted roofs have been well-proven for both extensive and intensive green roofs and are a structural solution with long lifespan. The main advantage of the system is providing thermal and mechanical protection against rainwater by the thermal insulation boards.
The production process used in the manufacture of extruded polystyrene (XPS), results in a homogeneous, closed-cell material structure with a smooth surface (called the extrusion skin) which provides:
- consistently high thermal insulation level
- water and frost resistance
- high strength
- high flexible rigidity
- high resistance to vapour diffusion
All of these favourable characteristics make the XPS thermal insulation material suitable for green roofs.
Extensive green roofs are principally created for their ecological aspects. The entire thickness of the layer is usually between than 6 to 15 cm. Roofs with the thinnest vegetation blankets weigh around 45 to 60 kg/m2, while thicker ones can be 160 to 250 kg/m2 when wet. In well-functioning extensive gardens or roofs, the plants used must be well adapted to drought and require little care.
Soil mixtures with high water-retention capacity or special mineral substrates that also act as a drain layer can be used as a topsoil layer. In the case of the latter, there is no need for a separate drain layer, and a thickness of min 6 to 10 mm is recommended. The root network of the contiguous vegetation also provides for the stability required against wind-load, however, additional ballast is necessary along the roof edges and adjoining surfaces, and along the edges and in the neighbourhood of floor gullies gravel ballast strips and surfaces must be formed in line with roof insulation guidelines.
Intensive roof gardens are roof gardens with a minimum 30-cm thick plantation soil layer, which may even be identical to the garden in the courtyard of the house. The thickness of the vegetation layer is restricted only by the load-bearing capacity of the roof slab, and, if the soil is 1 to 1.5 m deep, even small-sized trees can be planted. Typical forms of roof gardens are gardens for relaxation, children’s playground or parks, but even vegetable gardens are possible. These kinds of roof gardens have the same versatility as a normal garden, so they require regular maintenance, irrigation and appropriate nutrient supply.
The type and composition of the topsoil for intensive roof gardens as well as the crop to be planted should be determined with the involvement of a garden designer. The wind protection of tall plants should be professionally anchored and supported.
INSTALLATION OF GREEN ROOFS
The rainwater proofing material for green roofs should be resistant to roots (e.g. FLL certification) otherwise the installation of a separate layer for protection against roots will be necessary. Although, XENERGY™ XPS boards provide additional protection to the waterproofing membrane, they cannot replace protection against roots.
The vapour-permeable layer laid on top of the thermal insulation prevents fine granules from being washed into the drain layer or between the thermal insulation boards, and provides mechanical protection for the surface of the boards.
To ensure the vapour permeability in a 30 to 40 mm thick washed gravel, crushed stone, expanded clay aggregate or various special products (drain carpets, profiled drain plates etc.), or light-weight combined systems may also be used to ensure free departure of migrant vapour through the thermal insulation.
In green roofs, irrespective of whether it is an intensive or extensive solution, a topsoil layer with special composition is required, and the vegetation should be carefully selected.
IMPLEMENTATION OF GREEN ROOFS
The material of rainwater proofing of green roofs should be resistant to roots (e.g. FLL certification) otherwise the installation of a separate layer for protection against roots will be necessary. Although, the STYROFOAM™ XPS boards provide additional protection to the waterproofing membrane, they cannot replace protection against roots.
When implementing slope and water drainage, it is an important aspect that SPX boards should not be persistently under water. It is a fundamental design condition that the screed of XPS boards must ensure a slope of at least 2%. (Non-slope roofs have not delivered as expected even when fully protected waterproofing materials, e.g. green roofs, were used!)
In intensive roof gardens, the use of permanently flooded drain layers is to be avoided.
The vapour-permeable layer laid on top of the thermal insulation prevents fine granules to be washed into the drain layer or between the thermal insulation boards, and also provides mechanical protection for the surface of the boards. It is important to build them in in every case.
Over the thermal insulation, as a drain layer, a 30 to 40 mm thick washed gravel, crushed stone, expanded clay aggregate or various special products (drain carpets, profiled drain plates etc.), light-weight combined systems may also be used to ensure free departure of migrant vapour through the thermal insulation.
The use of expanded clay aggregate or keramsite as a surface drain helps to efficiently and quickly drain water and also acts as a water storage layer. In this way, the necessary water remains on the roof, but the excess will be drained.
With respect to thermal insulation materials, XPS thermal insulation boards provide in an impeccable solution. In consideration of the highest loads, the appropriate material is at least 300 kPa. In normal cases, the boards are to be installed in one layer, in offset bond, the fluted-edge boards with tight joints, in the thickness complying with thermal dimensioning.
In green roofs, irrespective of whether it is an intensive or extensive solution, a topsoil layer with special composition is required, and also the planned vegetation should also be carefully selected.