Planning Aids Wind Up-Lift Protection
Because of the climate change roofs that are higher up or exposed are exposed to increasingly stronger winds.
The current DIN EN 1991-1-4 (mit NA) "Wind Loads" addresses these new issues. In regards to green roofs one has to differentiate between wind up-lift protection and wind erosion protection and take this into account for planning.
Wind Up-Lift Protection
No matter what green roof type is used wind up-lift protection always entails securing and fixation of loose or partially fixed roof membranes through superimposed load with gravel, paving or roof greening. Suction forces have an effect on the roof membrane that is connected to the substructure. Depending on the green roof system the suction forces can be reduced by a factor of R.
Wind Erosion Protection
A green roof must not only have wind up-lift protection but must also be wind erosion proof. This is the case when the wind is not able to blow single grains of gravel or substrates off the roof. Wind erosion protection can be tested in a wind channel.
The technical department of Optigrün international AG proposes the following measures in case the roof is vulnerable which should already be considered during the planning phase and proposal:
- Gravel strips at the edges and corners. Extremely exposed buildings also need grid paving filled with gravel.
- Depending on the object location, vegetation mats are used at the edges and corners of the green roofs.
- The central parts of the green roofs can usually be planted using hydro-seeding which is sufficient for wind erosion protection. Taller buildings (wind zone 3 and 4, exposed roofs) usually require the use of vegetation mats.
- For pitched roofs the verge, roof edge and ridge are vegetation-less.
- Regular and professional care and maintenance.
- Object specific calculations using the proved, system specific reduction factor R - a free service of Optigrün international AG.
Reduction Factor for Green Roofs
Depending on the used material and vegetation different reduction factors may be found; this means that a system solution inspection is necessary. The Optigreen System Solutions were tested by the IFI Aachen and show reduction factors of 0.4 to 0.6. The reduction factor is greater when the roof membrane is fixed to the substructure. For a proved reduction factor R the green roof build-up may be designed significantly lighter and the fixation of the roof membrane can be reduced due to the superimposed dry weight of the roof greening:
- Reduction of the used roof membrane fasteners depending on the necessary green roof weight
- Reduction of the layer height of the green roof
- Because of this a reduction of the supporting structure / substructure is possible, because only a lighter and smaller green roof build-up is required