Siphonic Roof Drainage: Rocket science? I don’t think so


By Mike Richmond S


ince the first major construction in the U.S. incorpo- rating siphonic roof drainage (SRD), the Boston Convention and Exhibition Center, was completed


in 2004, many questions have been asked by contractors, owners, architects and engineers, and many a furrowed brow has been seen on the so called experts and specialist manufacturers and distributors. Why has there been (and continues to be) such scepti-


cism about the use of what is, on the face of it, a simple piped rainwater disposal system? Many of the readers of this article will have at least


heard of the system if not participated in one of the many seminars or presentations that have taken place in the last five years or so. Hopefully, some will have been involved in one of the many projects that have embraced the system. Those directly involved in the market will be aware of


SRD’s wider use in recent times. Something has triggered this recent change in attitude. There are a number of pos- sibilities for this change: • The market decision makers have been browbeaten by


the various system proprietors. • The decision makers embrace innovation elsewhere,


why not this? • The recent hard times have given the decision makers


time to listen to the proprietors. • Cost savings are now as important, if not more impor-


tant, than they once were. • The great selling tool is the fear of loss. • It actually … works. As far as I’m concerned, too many articles have already


tried to explain the complex mathematics and science that makes SRD tick. Let us assume that the smart guys have fulfilled that task, and let us look into the practical work- ings that bring benefits to builders and owners.


Commercial The first comment usually made is that, if the pipe is


smaller, it must be less expensive. This is correct, but far from the end of the matter. Involving SRD at the outset of a project can significantly reduce the amount of pipework, as well as reducing the size, and can reduce the extent of civil works below the building or below ground externally. Many projects are presented as a gravity design, partic-


ularly in buildings where the pipe system is located in and above the ceiling location. In office buildings, schools and medical buildings, for example, the extent of the routing is governed by the available ceiling void. This usually forces torturous extended routing in order to find suitable drop locations. With SRD, you simply pick your elevation, con- nect the line of drains in the most direct route and connect


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The Boston Convention and Exhibition Center was the first major construction project to incorporate siphonic roof drainage.


it to the most convenient downpipe discharge location, either within the building or on its perimeter. Remember, the pipe runs truly level and is smaller in diameter. What are the downsides? Field changes and modifica-


tions cannot be left in the hands of the installer; these must be referred back to the designer for verification. An installer’s first project is quite rightly met with uncertain- ty and some trepidation. After a cautious start, all in my experience have come back with significant praise of the system’s simplicity and the question “Why have we not been doing this for the last 10 years?”


Constructability and coordination SRD is a piped rainwater system. In most cases, it uses


the identical materials to a gravity system. In some cases, it can even use the same roof drain (with slight modifications), so there is little to be afraid of with respect to the basic construction. The big winners are as follows: 1) Smaller pipe means less cost, less space required, less load on the structure, less weight for the installer and 2) Level installation makes it much easier to install and simpler to coordinate with other trades — set up a laser level to the crown of the pipe — same bracket lengths throughout.


Environmental The big green word. Less material use is the obvious


gain. Controlled flow discharge is a further benefit, and SRD’s simplicity of co-ordination and flexibility gives rise to benefits when used in conjunction with rainwater harvesting.


In summary What are we all so worried about? I met one plumbing engineer who is adamant that SRD is far too risky, the physics do not work, that the flow patterns are too dynam- ic around peak. It is a disaster waiting to happen. Last time I met him he was 2,000 miles from home. I asked, “I pre- sume you walked here then. Surely flying is too risky!” Tens if not hundreds of thousands of SRD systems have


been installed worldwide, I suspect that the United States has hundreds, shortly thousands, of installations. It does not rain here any differently than it does in the rest of the world. n


Mike Richmond “joined forces” with one of the U.S.


drain manufacturers in 2007. He has been involved direct- ly as a design-build SRD contractor for the better part of 18 years, covering the UK, Europe, the Caribbean and, more recently, the U.S. and the Middle East. Richmond has been involved in thousands of different projects.


June 2011


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