Legend
- Sub-shoulder
- Shoulder
- Precipitation retention cell
- stud
- Diffusion opening/perforation
The ArchiGreen® UltimateDrain 40 is a black water reservoir and multi-directional runoff-delay drainage board made of recycled high impact polystyrene (HIPS) for use on virtually all types of 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.