Looking across a paved area towards a drain, water removal seems like a simple equation: surface water will be directed across the plane, through the channel, and then moved away to the stormwater system. However, a podium or suspended slab with a habitable or dry space below requires additional considerations, and careful planning must be made to control both surface and subsurface water. Additionally, the system design must consider factors such as loading, available fall, and aesthetics.
Once the base slab is poured it will be membraned to create a waterproof enclosure that protects the area below. Careful attention must be paid to any penetrations in this layer. Using the podium drain system from Allproof, the membrane can be clamped so surface and subsurface drainage can be managed – this is installed into the concrete base slab, providing a flange for the membrane to be dressed onto. A specialized clamp ring secures the edge of the membrane and provides an escape for any subsurface water.
It is often thought that a tiled or paved surface will provide a complete surface to direct water to the relevant drain. In reality, tiles are porous, grout can crack and concrete has many fissures that allow the surface water to track through the topping/wear slab to the membrane below. Weeping penetrations in a basement carpark roof, which shows that a penetration has not been adequately fitted off, is an example of this. The build-up on top of the base slab will vary depending on the requirements of the finished surface. Generally, a drainage cell and filter media are installed on top of the membrane to facilitate drainage – after which a wear/topping slab is poured as either the finished surface or base for tiles to be applied.
The surface water drainage system must be designed to all applicable Australian Standards. The selected drainage outlet or channel will be connected to the previously installed podium base via a cut-to-length PVC riser. This completes the function of the podium outlet, collecting surface and subsurface water through a single outlet. Point drains, such as those from the Allproof Storm Series, provide a subtle outlet that has excellent hydraulic properties and can be attached by O-rings to the PVC riser.
Where a longer run is detailed, a channel drain may allow for shallow falls, with outlets along the run being dropped into the podium bases below. Early planning by the main contractor will ensure outlets are aligned with the finished channel when it's installed in the base slab to final fit-off dimensions. Melbourne's South Warf has successfully implemented this system. A 75 mm deep polymer concrete channel with wedge wire grating was selected due to the shallow wear slab and tile combination finish.
Allproof's selection of stocked products creates systems that will help you detail a reliable drainage solution to meet the aesthetic and performance requirements of your project.
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