RUNWATER DOWNPIPE CALCULATION IN MALAYSIA

Today I have a task of calculating number of RWDP to be proposed for my project.  So first thing firts, I must use the correct way because it's very important to have a sufficient RWDP in order to prevent a flood.

Parts of a UPVC downpipe

GUTTER CAPACITY CALCULATION
Input roof catchment size for one outlet (m) 8.4m width 34.3m lenght
Roof Catchment Area(m2) 289m2
8.4m x 34.3m = 288.12m2 per RWDP 

Rainfall Intensity (mm/hr) (Malaysia) 325mm/hr
Total cross section area of gutter 65790mm2

Gutter width based on structural design/site condition 300mm

Min Average gutter height including 25mm freeboard 245mm
(between lowest & highest point)

Gutter gradient 1:200
Minimum gutter girth (mm) For 1.0mm thick Zincalume gutter 814mm
Minimum gutter size = 300mm(W) x 300mm (D) 900mm

CAPACITY FOR EAVE GUTTER
Downpipe Capacity for Eave Gutter
Cross section of RWDP for EAVE gutter = 95mm2 x Roof Catchment
Based on above roof catchment,
The requierd cross section of RWDP 27455 mm2
Min Recommendation diameter for RWDP = 200mm 

CAPACITY FOR INTERNAL BOX GUTTER
Cross section of RWDP for Internal Box gutter = 95mm2 x Roof Catchment
Based on above roof catchment,
The requierd cross section of RWDP 27455 mm2
Min Recommendation diameter for RWDP = 200mm

Components in a standard RWDP system

A cross-section showing the location of RWDP at any building.

Final installation of RWDP.

Images sources : Google