Four years in the making, the $40 million, 8,100 square metre Bunnings on the Frankton Flats, Queenstown, finally opened earlier this year.
Bunnings first applied to council to build the Queenstown store on the 1.6-hectare site in April 2017, but was declined, leading Bunnings to appeal the decision to the Environment Court and finally getting approval for site works last year.
Now, standing tall under The Remarkables with the largest trade yard of any New Zealand Bunnings, business is booming and they’re proud to be supplying important building materials to support the local construction sector.
But, big buildings need big drainage so the Marley Akasison siphonic roof drainage system was chosen to cope with the imposing structure, in an area known for its environmental extremes, including snow and sudden, massive dumps of rain.
We spoke with some of the key partners involved in delivering Bunnings Queenstown to learn more about the factors that made Akasison the right drainage solution for this landmark project.
Main contractor for the Bunnings Queenstown design/build project was Milton head-office based Calder Stewart Industries Ltd/Calder Stewart Construction.
Paul Smith, National Design Manager says that despite the complex planning process for the project, the build itself was relatively straight forward with a prefabricated steel structure, Kingspan panels and roofing.
One issue however, was to provide adequate roof drainage despite the client’s brief for no visible downpipes on front face of the building. That made Akasison the ideal solution.
“When we do design builds, typically we find the projects have been designed with a traditional drainage system,” Smith says.
“But when you get into the detailed design and you realise it actually doesn’t suit a traditional method, because you can’t have the downpipes where you need them.
“That’s when we contacted Marley and looked at a siphonic option,” Smith says.
Siphonic systems use the unique properties of water to draw the water down the pipe at a much faster rate.
In traditional roof drainage the water spirals down the downpipe, with a tunnel of air in the middle, so only a limited amount of water is discharged. That means multiple downpipes are required to handle the total load during heavy rain periods to stop water overflowing out of the gutters.
Siphonic systems require fewer, smaller downpipes because the system gets loaded and the water fills up and drops down the downpipe without the air tunnel. This means the water volume is cleared much faster. And the pipework can be installed horizontally and close to the roof with no gradient.
Paul Smith’s first experience with siphonics was using it for a cinema complex project in Christchurch, which had a long internal gutter, but, like Bunnings Queenstown, nowhere to put downpipes. Smith saw siphonics as the best solution and was impressed with the result.
Now, Smith has introduced the system for the new, Port Otago building in Port Chalmers as well, “because it’s all glass and no one wants to see downpipes,” he says.
Smith says that there are significant planning benefits in using the Akasison system.
“With the speed that many projects are being developed in these days, there’s often not enough time to have the design finished to see where all the downpipes are, and to get all the drains cast into the floor.
“If you’ve only got one connection point it’s easier. Instead of having multiple vertical downpipes, you’ve only got the one vertical downpipe, depending on building size, so you can make a duct space or a set out, and that’s where all your siphonic system can go to,” he says.
Smith works with the Marley design team to do the concept for budgeting, and once all details are agreed with the plumber, it goes back to Marley for the detailed design phase. Then, all the documentation is ready for the building consent.
And Smith says the councils like it.
“If you show them, “Here, Marley have designed it for us. Here’s all your documentation you need,” they usually go, “Cool. Tick the box”.
And Smith says the system stacks up well for those “big, big, projects”.
“Even if there is a premium for siphonics, when you weigh it up against the simplicity of maintaining the client’s brief of clean walls, or the fact the architect’s given us no space to put any services in, it helps solve those issues for us and more than makes up for any difference”.
Peter Diver Plumbing was the subcontractor for Bunnings Queenstown and Director, Michael Diver has used a mixture of siphonic systems for different projects over 15 years, but says Marley is definitely his preferred option.
“We’ve done other siphonic systems in the past, but Marley has a different clipping and rail system compared to others. The overall product looks a lot better and it allows for expansion and contraction a lot better than other systems out there, so it will give a lot longer life.”
Diver says that prior to the Bunnings job, his team had been involved in a much larger installation in Christchurch with the Marley system at Waimakariri Multi-Use Sport Facility, in Rangiora.
Diver says that the first time using siphonics was “definitely an eye-opener.”
“When you run a 75mm pipe where you’d normally have a 200mm pipe, you do question yourself. But then, when you see it working, it’s quite surprising how much water it actually sucks out.”
Diver got a chance to see the Akasison installation get a solid workout this year, with big one-in-200 year rain events hitting both Queenstown and Rangiora. Diver says that the team went out to see how the systems were coping and found both were well within capacity.
“You just have to trust the Marley design team to specify the right system.
“It can look quite daunting to start with, but the Marley guys are really good. They come down and do training. They run over everything with you, give you really good documentation with plans, fittings list, measurements, everything like that. So once you actually drill into it, it’s actually a lot easier than it looks.”
So, why does Diver think siphonic systems are not more extensively used?
“I just think it’s lack of knowledge from consultants. If they saw the benefits of it and the cost savings and the time and space savings they’d use it more. Those consultants just don’t get to see what it is and how it works,” he says.
Self-employed Plumber Dave Weight of Ezyplumb contracted to Peter Diver Plumbing on this project and said it was a relief to not have to wrangle massive pipes on the Bunnings job.
He says it was a relief to not have to wrangle massive pipes on the job.
“When you have big pipes that have got fall on them, they always hit an aircon duct sooner or later. And putting in a 125mm or a 80mm siphonic is a hell of a lot easier than trying to put 150mm PVC in and getting the ends together and all that,” he said.
Weight says the Bunnings project was a good one for him to start on, with a ‘small’ 120 metre straight run.
“I got to see it in action. It started raining and I actually opened up the inspection lid that was at the very end of the line where it goes into the 200mm.
“Obviously on a normal system, if you open that lid, you are going to get absolutely saturated. But I took the lid fully off and there was just a solid 125mm column of water blasting past that inspection lid.”
Weight said that getting all the plans from Marley, with a full list of materials and measurements made the process even easier.
“I’ve done bits and pieces on other systems, but that’s the first time I’ve done a whole system. I thought it was cool. It was definitely a process, but it wasn’t really that difficult and I liked the end result.”
Developer: Bunnings (NZ) Limited, Owen Sanders (Project Manager)
Main Contractor: Calder Stewart Industries Ltd/Calder Stewart Construction
Plumbing subcontractor: Diver Group/Peter Diver Plumbing, Michael Diver.
Installer: Dave Weight