ArchiGreen

Legend

• 1 Diffusion opening
• 2 Precipitation retention cell
• 3 Stud
• 4 Shoulder

The ArchiGreen^® SedumDrain^® 25 is a black water reservoir and multi-directional runoff-delay drainage board made of recycled high impact polystyrene (HIPS) for use on intensive, semi-intensive and extensive green roofs. The board is thermoformed on both sides with precise 2 mm perforations at the centre of the studs composing its top surface. These perforations are known as diffusion openings. Between every adjacent two studs is a raised dam known as the shoulder. Collectively, these shoulders form the precipitation retention cells that store rainwater and attenuate stormwater runoff. One row of precipitation retention cells is known as a corrugation.

When SedumDrain^® 25 boards are laid on a green roof site, the boards are laid in an overlying tile manner, beginning at the roof outlets and working up by placing each board on top of the one already laid down with one or two overlapping corrugations at the edges of the board. This overlying tile manner of installation ensures that the water flows in the direction of the outlets. Please note that the diffusion openings of SedumDrain^® 25 should point upwards when installed beneath vegetated areas on a green roof whereas the very same openings should point downwards if installed under paved or vegetation-free areas. This is because under non-vegetated areas it is strongly advised that boards do not retain water unnecessarily. Connecting the SedumDrain^® 25 boards by overlapping the corrugations at their edges is referred to simply as overlapping and plays a paramount role in combatting urban flash flooding as will be pointed out below. SedumDrain^® 25 forms the perfect water reservoir and drainage layer in a green roof build-up. The diagram below shows the operational principle of SedumDrain^® 25 followed by a concise explaination:

1. A good green roof substrate will act as a buffer in the case of urban flash flooding and will absorb water to the point it gets saturated thereby, mitigating stormwater runoff. This temporary effect of runoff delay and reduction is known as vertical detention and depends on the physical charecteristics of the substrate. Once the substrate is saturated, rainwater percolating through the FL filter sheet is stored in the precipitation retention cells.

2. When the precipitation retention cells are filled, excess water flows over the shoulders, then over the edges of the boards, into the corrugations of the other boards placed below them and this waterflow continues all the way until it reaches the outlet, while momentum and speed of the water passage is being reduced with every raised dam or shoulder. This is known as horizontal detention and is a very important temporary effect when it comes to stormwater management and combatting urban flash flooding. The double-sided shape of SedumDrain^® 25 resulting in the raised shoulders all over the board and the overlapping manners in which this amazing board is installed, ensure its undisputable role as a sustainable drainage system (SUDS) and in combatting urban flash flooding.

3. During times of heavy storms, water may leak between the overlapping gaps at the overlapping corrugations. This is absorbed by the PL protection mat. Unabsorbed water shall flow to the roof outlets through the drainage passages underneath the drainage layer.

4. As the drainage layer dries out through vegetation usage and evaporation, the damp PL protection mat releases its moisture gradually through the diffusion openings helping to keep the substrate moist.

5. Jointly with the diffusion openings, the bottom channel system ensures the aeration of the root space and prevents it from getting stuffy. Consequently, diffusion openings are sometimes referred to as venting holes.