Appendix U — Determining Catchments Area for a Flat Surface

Figure 8.U.1 shows a building having flat roofs at different levels. In level 3 the area ABCD is the catchment area contributing to the rainwater down pipe RDP1.

In level 2 horizontal area EFGH and 50% of the vertical wall surface area AFHM, projecting above is the catchment area of rainwater down pipe RDP2.

For the rainwater down pipe RDP3 the catchment area will be the terrace at level 2, 3 and fifty percent of the adjacent contributory wall AFHM, GHIJ and MJLC.

Figure U.1 Catchment area of flat roof and surface wall