Cut overhead costs

A siphonic roof drainage system is less expensive, more effective.

The best money-saving ideas don’t have to be new – they just have to be new to your operation. In fact, ESI Design is introducing U.S. food plant and ware­house operators to a distinctively differ­ent approach to roof drainage. The results just might excite you.


Traditional storm water roof drainage is simple. You calculate the amount of rain­fall on an area of roof and size the pip­ing using charts in the mechanical code. The downside to a traditional system is that the piping is very large (often 8 to 12 inches in diameter) and all horizontal pip­ing must maintain a consistent downward slope to guarantee flow. Here, the pipe is only partially full of water and therefore not fully utilized.

Siphonic roof drainage is different. It’s a newly accepted approach that utilizes smaller piping (than code typically allows) and horizontal pipe can run without a slope because it uses the entire pipe.

Special roof drains keep water from swirling, which eliminates air in the pip­ing and smaller pipe keeps the pipe full. Because it uses suction – rather than gravity- to pull water through the piping, it is not necessary to maintain a slope. The result is a piping system that functions like a straw and sucks the water off the roof.

It uses common hydraulic principles to move water more efficiently than tra­ditional systems and has been effectively proven for many years in Europe. Only recently have United States build­ing code officials acknowledged this new practice. Several manufacturers now make siphonic drainage components and many of them will assist with system design, if requested.


The best candidates are new building opera­tors who will need internal roof drainage very far from the exterior walls of the building.

In typical warehouse spaces, it’s not uncommon to see roofs that are several hundred feet wide. If an internal drain is needed in the middle of this kind of roof, a siphonic system can utilize smaller piping (4 to 6 inch diameter instead of 8 to 12 inch diameter) and run to an exterior wall with­out sloping. This also may eliminate any problems with racking interference.

One siphonic drainage supplier says building operators can save 35 to 65 per­cent in costs compared to standard sys­tems. Smaller piping is less expensive and allows for easier installation thus lowering labor costs and is easier to support which reduces structural costs.

Also consider that …

… operators can eliminate most drain­age below the floor of a building;

… there’s more valuable building space due to fewer collector pipes to convey water to the building perimeter;

… HR Wallingford and ASME have inde­pendently tested and approved these sys­tems against various code requirements (EN 12056-3:2000 and ASME 112.6.9-2005). Most of the facilities ESI designs involve (1) sheet drainage, whereby a roof slopes to the edge of the building with water col­lecting in downspouts; or (2) existing facili­ties with drainage systems in place. At the request of a new client, we were asked to design our first siphonic system for a green­field warehouse/ retail distribution facility . We will continue looking for opportuni­ties where we can apply this new system.

By Charles Discasey & Jon Olson

Discasey is a senior mechanical engineer and Olson is a mechanical engineer with ESI. Combined the two have more than 20 years experience with food, beverage, and cold storage warehouse industries.


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