Drainage and moisture retention layer, which is placed at the base of the system, above the waterproofing and before the substrate is laid, is essential for the proper functioning of a green roof. Laterlite Agri lightweight aggregate is the ideal product for the granular drainage of roof gardens and green roofs (both extensive and intensive), or in pots and planters, because:
- It has very good draining action: the dense network of voids between the granules (55 %) optimises the run-off of excess water and prevents damage from water stagnation
- It retains moisture: the pores within the granules have very good water retention (up to 30%) and releases it slowly, giving plants a valuable water reserve that ensures their long-term health and reduces water stress in hot weather.
- It is lightweight, which helps to avoid overloading the structure of the building
- It is simple and quick to put in placeas a granular material that is laid loose and is easy to level
- It is strong, stable, and durable: will not deform, break, or become compacted over time, and is resistant to freezing and high temperatures.
To construct a drainage layer of this type of the expanded clay is laid on the waterproofing and a filtering layer is placed on top, separating it from the substrate above. The thickness of expanded clay will depend on the climate and whether the planting system is intensive or extensive.
- Granular Laterlite Agri 8/20 or 3/8: for maximum drainage and lightness. In intensive or semi-intensive roof gardens where the substrate is 20 cm deep or greater, a draining layer of granular expanded clay at least 5 cm thick it is particularly recommended.
- Crushed Laterlite Agri 5/12: for maximising the moisture reserve. Particularly recommended for extensive types of rooftop cultivation as a drainage layer of limited thickness (lower than 5 cm).
Ultra-light pervious concrete based on expanded clay, such as Latermix Cem Classic, can be used as a highly stable porous permeable layer that allows rainwater to run off freely following the slope of the substrate. It can be used as a drainage layer under hard-paved transit routes or recreational areas, or below small buildings, supported by the drainage layer.
Drainage layer support must be covered by a waterproofing system, provided with slopes and a suitable rainwater evacuation system. Laterlite lightweight screed mortars are ideal for creating the falls and as a support for waterproofing at the base of the green roof system.
See also the pages: Green Roofs Growth Substrate, Intensive and Extensive Green Roofs and Rooftop gardens and green balconies