Gutters must be installed with a sufficient fall to the downpiper to enable the rain water to drain freely form the roof drainage system.
size and fall of gutters
eaves gutters -----onece in 20 years
intemal box gtutters -------onece in 50 years
vallay gutters------------onece in 100 years
Gutters ,downpipers and flashings must be manufactured in accordance wiith the A S 2179
for metal compnentsand AS 1273