The growing value of siphonic roof drainage: an interview with Amanda Gibbon, Technical Sales Manager

min read time
2023-09-13 09:14:59

Amanda Gibbon, Commercial Technical Sales Manager at Wavin specialises in Siphonic Roof Drainage (SRD) systems within the commercial and public industrial market. As an active member of the industry body, the Siphonic Roof Drainage Association (SRDA), Amanda is at the forefront of SRD evolution. In the light of growing interest in how SRD can support greater sustainability in a build, we caught up with Amanda to get her specialist view.

Q: Welcome, Amanda! Can we start with a little on your background with Wavin? 

AG: Well, I joined Wavin in 2009 and soon found my niche in commercial products. I started out in Swindon, and now I cover Wales and the Midlands as Commercial Technical Sales Manager, supporting commercial industrial projects. About five years ago, siphonic roof drainage stole my heart a bit, and it’s become an expert focus of mine. And developing that expertise has been critical to establishing my credibility as a woman in a male-dominated industry. But things are really changing now and, today, more women are having great careers in construction – as installers and site managers, and behind the scenes as designers, architects and commissioners. I love to see that. 

Q. So, as an expert in the field, why do you think siphonic roof drainage is more visible within the construction industry right now – what’s changed? 

AG: It’s an interesting one. Siphonic roof drainage isn’t new. The first commercial installation took place in 1972 in a Swedish turbine factory, and the construction industry has been using the high-capacity, low-maintenance system powered by negative pressure ever since. It’s the accepted way of removing water quickly and efficiently from large roofs. 

What siphonic drainage can achieve hasn’t changed, but the industry context has. The shift is driven by the world waking up to the climate emergency, and realising that we need to manage our impact on the planet by increasing sustainability. Construction generally, and particularly those who commission builds, are under pressure to find ways to deal with the effects of climate change. Siphonic roof drainage is now getting recognition for the sustainability benefits it has been delivering all along. This is excellent progress, and I’m doing all I can to get SRD systems the sustainability recognition they deserve from project commissioners through to architects, design specialists, engineers and site teams. 

Q. To help non-specialists fully understand where these benefits come from, what exactly is an SRD system? 

AG: To fully explain that we first need to take a small diversion to look at the alternative, older approach – a gravity roof drainage system. 

In a gravity system, when water flows in the downpipe it forms a vortex and spirals round the inner wall of the pipe, leaving an air-filled core down the centre of the water flow. About a third of the pipe is filled with water, and the remaining two thirds are air, so the drainage is really inefficient. This means to cope with a large water flow, you need a lot of pretty big pipes and, even then, you can’t be completely confident that the system will cope. Because of this, gravity systems aren’t the standard approach for draining large, sometimes complex roof areas anymore. 

Siphonic roof drainage systems have taken over because they offer a much greater capacity. SRD systems work by restricting air entry into the pipes to create a full bore flow. During normal rainfall conditions, the system operates as a traditional gravity system. Then, in heavy rain, once the system’s ‘design rainfall’ is reached, an anti-vortex baffle in the outlet prevents air from entering and the system fills with water. The combination of no air and the water’s gravitational pull creates a vacuum, so the system is primed (fully filled) and operates at full flow capacity. On average, an SRD system drains water ten times faster than a gravity flow system. The siphonic action is broken at the connection with the below ground drainage, and the first adjoining manhole should be vented to provide atmospheric pressure in order to break the siphon. 


Q: So, SRD systems are much more efficient – has that been their main attraction to the market? 

AG: That’s been a massive part of it, but this efficiency boost also unlocks cost savings that are a big plus for developers in today’s tight economic environment. Basically, an SRD system takes less pipework than a gravity system, and it can use smaller diameter pipes – which cuts costs. For example, I know of a 6,000 square metre roof that fitted an SRD system and cut the overall pipe length needed by 47%, as well as shrinking the pipe diameter; the old gravity drainage needed a pipe range of 160mm to 450mm, but the SRD system only needed a range of 56mm to 200mm. Siphonic drainage also needs fewer roof outlets and downpipes, saving money on materials and reducing the amount of groundwork installation needed. And, as a bonus, their high flow rates mean siphonic systems are self-cleaning, cutting operating costs.

But the benefits go wider than that. SRD systems take up less room within a building and are more flexible in design terms, giving architects more freedom and scope. For example, you don’t need to install pipes on a gradient, and you can put downpipes wherever it’s most convenient – and that can even be inside the building, which can make the exterior look more attractive. And, because the pipes aren’t on a gradient, they’re easier to seal. With less overall pipework to fit, it cuts installation time and resources, speeding up the construction schedule. 

Basically, siphonic roof drainage systems mean less, less, less – which is always a good thing on site. 

Q: Is this where the sustainability gains come in? 

AG: Yes, ‘less’ is a part of it. In green construction we talk about ‘dematerialisation’, which means using the minimum amount of material to achieve the functionality you need. SRD systems definitely link into this because they cut down the amount of pipework and get more functionality out of what pipework there is.

But they are also a piece of a wider sustainability approach in construction. Developers are really waking up to how climate change is making heavy rain downpours more of an issue. They’re realising how critical it is that their buildings can handle moving huge amounts of water from the roof, to avoid flooding off the rooftop into the surrounding area and even into the building itself. So, at Wavin we’re seeing an increase in SRD system take up, but also in developers taking a wider view of rainfall management. We’re talking more about sustainable drainage systems (SuDS) and looking at how developments as a whole can be smarter about collecting and distributing rainwater in environmentally friendly ways. 

It really warms my heart to see sustainability becoming a mainstream topic in construction. It’s been part of our Wavin DNA for a long time now, and we’ve been pushing it forward with our customers and the industry. Now, people are listening. 

I believe we’ve got to step up and give something back because, unfortunately, human beings are doing things to this planet that it doesn’t like. I love being able to use my role and experience to spread the word and to share the Wavin way of bringing sustainability in early when planning any project.

At Wavin, we’re building a team to take a broader urban climate resilience approach, focusing on achieving amazing product efficiency and environmental benefits at the same time. 

Q: What does an urban climate resilience approach look like in practice? 

AG: It centres on tackling the challenges of floods, droughts, heat stress, groundwater depletion and surface-water pollution through smart innovation and design. 

From a roof drainage perspective though, it’s about bringing together an SRD system with SuDS at ground level to manage the water from roof to river. That’s how we’ve got to think now – roof to river. There’s no point taking huge amounts of water away from the roof at speed if there’s nowhere for it to go at ground level and it causes flooding there. There are all sorts of SuDS solutions that can help, like setting geocellular attenuation tanks into the ground around the building, to help out natural drainage with some manufactured capacity. Attenuation tanks collect excess water and release it into the environment via infiltration or, where that’s not possible, into sewers and watercourses at a manageable rate.

I’d also like to see developers making the most of the SuDS potential of the roof itself by creating a blue-green roof rather than the standard black roof with no sustainability features. With a blue-green roof, you combine a ‘blue’ rooftop water storage system with a topping of ‘green’ planting to create a surface that can absorb, hold and disperse water to stop damaging run off. Already, developers with one eye on the future are taking the blue-green option; project commissioners like the sustainability credentials it brings, and it’s something that planners are increasingly favouring. 

Coming back to SRD though, siphonic systems are a key part of a blue-green roof set up, as they’re by far the most efficient way to move water when you need to. In fact, they’re so critical that many developers fit a secondary SRD system as a back-up for extra protection. 

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Q: Is the industry ready to go full speed ahead on SRD? 

AG: Well, the technology is definitely out there, and has been for some time. I’d say the challenge is more that developers may not be aware of everything the systems can offer and might not have access to the expertise needed to deliver them well. SRD is a technical solution, and each building needs its own unique plan and implementation strategy, plus expert fitting. At Wavin, for example, we partner with a leading installation firm that has over 30 years of experience to give our customers complete peace of mind. 

Q: What’s the Wavin approach to SRD? 

AG: Well, the important thing is it’s not just an SRD approach – it’s an ‘everything’ approach to water transference. The beauty of Wavin is that we’re a one-stop-shop for everything a commercial project needs to manage water into a building, through it and away from it – which is something unique to the market. 

So, although we have deep expertise in SRD solutions, our true value lies in being able to achieve the best, most efficient outcomes by designing and delivering systems that work from roof to river – and we can also help you manage them on an ongoing basis. We can connect everything, with one linked solution that makes sure your building can release rainwater into the water system safely, at a flow level it can handle. 

In terms of SRD specifics, our core product is our QuickStream system, and we take care of all design and calculation requirements, using our own software – that I’m proud to say is the most sophisticated in the industry. Our pipes are primarily high density polyethylene (HDPE), but all our outlets have metal pins for extra reassurance that the risk of damage and breakage will be minimal. 

Our reputation for good engineering is really precious to us, and this drives us to keep looking for ways to further improve our SRD solution. For example, we’ve focused on making installing outlets as easy as possible by minimising the number of parts needed. In fact, lots of different parts of our roof to river technology and systems are innovative. For example, our push-fit Hep20 range is the only push-fit plumbing system with joint recognition, secure demounting and a 50-year guarantee. And our new generation of Tigris K5 Press Fit comes with our acoustic leak alarm that makes a loud whistling sound if there are any leaks. 

There’s lots more I could say, but the bottom line is, our SRD approach is comprehensive and designed to do the heavy lifting, providing all the expertise and support developers need. 

Q: Is promoting a sustainable approach something you’re working on as part of the SRDA? 

AG: Absolutely. I believe blue-green roofing is the future, and SRD is a fundamental part of that. So, we’re working hard as a group to champion SRD within the industry, while providing a recognised platform for specifiers. Because we’re a member, our customers know Wavin provides independently accredited software for drainage design to BS8490, pipework and clamping systems compliant with SRDA standards, and installation that uses SRDA-recommended methods. 

Q: And finally, to wrap up, what’s the message you’d like readers to take away from our discussion? 

AG: That siphonic roof drainage is a valuable part of a wider, sustainable roof to river water strategy. It can be a little complex, which is why we offer a complete service to take care of the technicalities and handle the process from start to finish. But its importance is only going to grow, so it’s worth investing time in understanding the possibilities. 

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