siphonic roof drainage data sheet/brochure 1, may 2009

Note: Document provided for illustrative purposes only. Please contact Richmond Trading for advice tailored to specific job requirements.

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SIPHONIC ROOF DRAINAGEData Sheet/Brochure 1, May 2009

ApplicationsBy using a siphonic system, smaller bore pipe with fewer downpipes can be used to more efficiently drain water from roof areas leading to cost savings

What Richmond Trading Can DeliverIn conjunction with our partners in this field, Aquaphonix Ltd, we can offer a complete package of design and installation of siphonic drainage for any project at a very competitive cost.We have successfully carried out over 100 installations in Ireland to date for projects varying from warehouses to schools, supermarkets, apartment blocks, concert arenas, hospitals etc.We have a highly skilled installation team with a project management and design section dedicated to this element of our business.

We have set out this presentation to cover the following pertinent areas•Explanation of Siphonic Drainage•Efficiencies & cost savings that use of siphonic drainage can achieve•Comparisons between siphonic and traditional drainage•Typical design details supplied for each project




What is Siphonic Draiange & how does it work?

Most downpipe systems have a very inefficient way of discharging water from roofs because water spirals down around the inner edges or walls of the downpipes in what is called annular flow (in the form of a ring),At no time does the water ever exceed a third of the capacity of the downpipes,the reason is that the downpipes are discharging two-thirds air and one-third water. Siphonic roof drainage works very differently. Rather than letting the water fall under gravity, which is what happens with traditional downpipes, it sucks the water off the roof at velocities up to seven metres per second. This means that instead of having downpipes every ten metres or so along the sides of large buildings, the water can be piped horizontally at roof level to almost any point in the building before being brought down to a single collection pipe at ground level.

With gravity flow the water quickly reaches a maximum velocity that it can’t exceed (about two metres per second). Also, there is so much air in the vertical downpipes that many are needed to discharge the volume of air and water from buildings. Siphonic drainage replaces these downpipes with a single large pipe full of water that discharges at a very high flow rate . . •The siphonic system works like a domestic water supply. A lot of pressure or ‘head’ that has been built into the water supply system drives the flow of water out whenever a tap is turned on in any part of the house.” “At no time does the water ever exceed a third of the capacity of the downpipes,”

•The system self primes (to exclude air), which creates an operating head that sucks the water to any point in the building. Priming is achieved by placing a metal baffle just above the outlet to restrict air intake. Excluding air makes the flow more efficient because pressurised water flow can be generated.

•Priming can easily be explained by emptying a bath of water. When the plug is released, you can see a spiralling air core going down the drain. If you place your hand over that air core above the outlet, the spiralling disappears and the bath empties much quicker because full flow conditions have been initiated




Cost Savings by using Siphonic drainage

• Smaller pipe diameters with a siphonic system can be used, reducing material costs.Full-bore flow within the piping reduces pipe diameter as compared to open-channel, traditional gravity flow. The smaller pipe size equates to savings in material. For example, a traditionally designed system calls for an eight (8”) inch pipe, a siphonic system of equal drainage capacity may need only a four (4”) inch or six (6”) inch pipe to drain the same quantity of water.

• Siphonic action permits level pipe installations allowing fewer vertical stacks, saving ground work and building costs.Traditional systems are designed to be atmospheric throughout and rely on pipe gradient or pitch to induce flow to the point of discharge. This pitch necessitates the pipe elevation to become increasingly lower as it runs laterally. Full-bore flow is achieved independently of pipe gradient in a siphonic system. The piping can be installed flat like any other mechanical system such as sprinklers and it simplifies coordination with other building elements. With siphonic piping being horizontal, the building height may be reduced by 3 to 4 feet, saving on construction costs.

• Driving head of the siphonic system is up to 100 times that of a traditional system (i.e. height of building vs. depth on roof).Siphonic roof drainage systems make full use of a building’s roof height to drive the drainage capacity. The resulting higher operating velocities (3 ft/sec up to 30 ft/sec) of a siphonic system further reduce pipe size and promotes self-cleaning of debris.

• In a siphonic system, due to the fact that there are much fewer downpipes from the roof, below-slab installation costs are minimized, thus reducing excavation, backfill costs and exterior underground piping.

• Within a siphonic roof drain system, stack and horizontal pipe locations are highly flexible.Level installation and freedom of placement of vertical stacks reduces buried pipe depths and the associated costs of trenching, bedding, shoring, and dewatering. The flexibility of stack placement also facilitates on-site rainwater harvesting by allowing flexibility for cistern locations either below or above ground.

• Level installation allows for longer lateral runs overhead thereby reducing or eliminating pipe installed below slab and the associated costs of excavation, bedding and backfill. If overhead, traditional drainage pipe has to quickly drop vertically to avoid a conflict with the ceiling, structural elements or HVAC systems. If below grade, the longer the horizontal run, the deeper the pipe trench must go to accommodate pitch. Siphonic systems reduce or eliminate these issues. This means there are lower site preparation costs




Comparison of Traditional gravity system and Siphonic Roof Drainage System




Typical Design details provided for each ProjectAfter consultation with our client, we ask for a typical roof drawing for the proposed project so that, having reviewed the detils, our engineering team can draft and issue an overlay drawing together with detail sheets outlining the proposed siphonic drainage

siphonic roof drainage data sheet/brochure 1, may 2009

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