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Siphonic Roof Drainage
Common in Europe, now gaining traction stateside
by William Verdecchia
All images courtesy Zurn Industries
ALL ROOFS ARE SUBJECT TO THE
DESTRUCTIVE EFFECTS OF SEASONAL
WEATHER CHANGES, ENVIRONMENTAL
CONDITIONS, LOADING, AND AIR
POLLUTANTS. ALTERNATE CYCLES OF
WETTING, DRYING, FREEZING, AND
THAWING CAUSED BY WATER LYING
ON THE ROOF LEADS TO EXPANSION,
CONTRACTION, AND ROTTING—THIS
RISKS DAMAGE TO THE ROOF AND
EVEN THE BUILDING SUBSTRUCTURE.
Drainage is a signiﬁcant component of roof design
itself. Roof collapses typically occur because water
accumulation exceeds the roof’s structural capacity.
With proper water drainage in place, many major
causes of failure are eliminated.
For this reason, siphonic roof drainage is coming
into its own in the United States. First developed
in Finland by engineer Ovali Ebeling in 1968, these
systems are used around the world—in Europe, they
account for one-ﬁfth of commercial projects. This
sustainable technology crossed the Atlantic in 1999 with
the Boston Convention Center’s installation as the ﬁrst
major example, and acceptance has steadily grown.
Siphonic roof drainage differs from conventional
gravity drainage in what is called ‘full-bore ﬂow.’
Unlike conventional drainage, a fully engineered
siphonic roof drain system prevents air from entering,
allowing the pipes to be completely full of water.
The unique component of a siphonic drain that sets it
apart from conventional gravity drains is the air bafﬂe,
which prevents air from entering the piping system
at full ﬂow and protects against debris.
48 the construction speciﬁer | march 2014
2/13/14 10:04 AM