conventional drainage system
A conventional drainage system can be designed
for large surface areas but does not cut off air flow
into the pipe. For this reason pipes are sized for filling
ratios of 20% or 33% (depending on national or local
standards and regulations) allowing considerable
amounts of air into the pipes of 80% or 67% of the
pipe section.
In conventional roof drainage, the outlets are
simple “funnels” installed on the roof covering and
connected to the downpipes which are as high as
the building and the water collectors which require
a gradient of at least 1%, are dimensioned for a
maximum filling factor of 70%.
When the water collectors are very long and it is not
possible to provide the minimum slope necessary
due to the limited space available, the only solution is
to increase the size of the pipes with a consequent
rise in installation costs.