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Atlantic Salmon Environment Technology & equipment +3 more

How a Shetland community company has upcycled many miles of salmon feed piping to make ‘the Arnold Schwarzenegger of polytunnels’.

Tom Morton thumbnail

Recycling redundant high-density polyethylene (HDPE) piping from dismantled salmon cages and feeding systems is becoming increasingly popular throughout the world, with companies such as Envorinex in Tasmania producing an extensive range of products, including matting and grids which are exported to the UK. In Scotland, the Oban-based company Fusion Marine produces a variety of upcycled HDPE products, including plastic outdoor furniture such as benches, as well as walkways, fences, bridges and waymark posts. The firm also makes pontoons and has supplied them to Marine Harvest Scotland sites at Kingairloch, Loch Hourn, Muck and Kilchoan.

In Shetland, no stranger to DIY recycling by crofters, you can easily find boat trailers and slipways made using salmon pipe as rollers and supports. But it is a tiny, homegrown community enterprise which has taken, so far, 25km of used HDPE salmon-feed pipe and turned it into a product which is achieving worldwide success: the so-called ‘Arnold Schwarzenegger of polytunnels’ – the Polycrub.

The Polycrub is a robust, durable and resilient polytunnel designed and produced by a homegrown community-owned company in Shetland. So-called ‘hoop houses’, using thin plumbing pipe and rolls of flexible polythene, are favourite DIY projects. But the use of very strong, recycled salmon-farm pipe and double-wall ‘hard’ polycarbonate has produced buildings capable of withstanding extreme weather conditions. So far, two of these structures have been built in the Falkland Islands.

The word ‘crub’ or ‘crö’ refers to a traditional Shetland structure used most commonly to gather or shelter sheep but also, with a variation in design, to nurture young kale plants (which would, when strong enough, be transferred to an open yard and grown for human and animal feed). In its traditional form a ‘planticrub’ was a round, open enclosure of dry-stone construction. Its circular walls would often slope inwards slightly towards the top, like a broch, in order to provide further protection from some of Europe’s strongest and most destructive gales. Planticrubs can still be seen throughout the isles and indeed are sometimes still used for their original purpose.

Their modern descendant, the Polycrub, has been designed and produced by Nortenergy, wholly owned by Northmavine Community Development Company, a charity which aims at developing and sustaining its home parish of Northmavine. Tunnels can be erected on site by the company, but Polycrubs have also be made available in kit form, with full building instructions. The design, which tensions twin-walled polycarbonate sheeting against the recycled feed pipes, has been developed over the past nine years so that it is now capable of withstanding “strong winds, snow and frost, collisions from airborne debris and vandalism”. Even the earliest, experimental examples are still proudly in use, having dealt with everything from full-on hurricanes to accidental collisions with flying wheelbarrows.

So how did it all begin? Drew Ratter is a director of Nortenergy, and remembers that NCDC was “casting around for something that would produce a bit of revenue”, when the idea of producing some kind of polytunnel came up. But what would be strong enough to handle the extreme weather conditions of Shetland? There had been many instances of traditional polytunnels “losing their skins” in the teeth of a gale, and something stronger was evidently required.

“I remember a group of us went off in a minibus one weekend to look at polytunnels round and about Shetland,” says Drew. “We didn’t see anything that was quite what we had in mind but one had used polycarbonate sheets and one had recycled salmon pipe as supporting hoops.

“We came back and designed something which used those ideas, and the notion of using second-hand salmon-farm pipe to make the hoops in the Polycrub was especially appealing, because there was a surplus in Shetland of used salmon pipe. And that was the original design.”

The pipes used in the Polycrub design come from feeding systems. In their original role, after a certain period of time feed pipes’ insides become rough and eroded, and so unsuitable for highly precise feed-supply work. They do remain very robust, though – indeed almost indestructible. The pipes, all donated freely to the project by the salmon industry in Shetland, also act as a thermal store for heat absorbed through the polycarbonate surface of the ’crub.

The original Polycrubs were built, says Drew, “according to an idea rather than an actual design”, but there have been constant improvements over the years.

“Through I guess basically word of mouth, news of them just got out. The most remote and distant ones we have now are in the Falkland Islands – we’ve sent two to the Falklands and there have been more enquiries. There’s a lot in Orkney and the Western Isles – they’re just incredibly suitable for places that experience high winds.”

So what is the basic design of a Polycrub? Essentially, the salmon pipe is cut to lengths suitable for providing a hoop-shaped support for four- or three-metre wide units. They’re the ‘rafters’ of the structure. Longitudinal wooden purlings support the polycarbonate sheets and are attached to the plastic pipes. At the end hoops, round posts are inserted into the pipes and concreted into the ground. The bottom edges are finished in wood, the ends and the doors with wood and polycarbonate. The result is in the shape of a Nissen hut, which was specifically designed so that the wind pushes it down rather than lifts it up.

There’s no sign that the supply of recyclable salmon feed pipes – around 25 kilometres of which have so far been saved from landfill – will dry up. According to Drew: “The salmon industry is in the Western Isles and down the western seaboard of Scotland too, so it looks as if, unless they change the way they do things radically, I would think there will be a good supply ongoing in the future. You could buy new pipe, obviously, but it seems ecologically sound and more in the spirit of combatting climate change if you can use recycled material.”

Now there are plans to market the Polycrubs more dynamically and perhaps extend production beyond Shetland to reduce distribution costs for orders from further afield.

“One of the problems we’ve had is that if you’re making these things here in Shetland you’re building in a fair bit of extra freight costs when you’re exporting them. We’re in discussion with various people about solutions to that. We’d like to do something which means we don’t have this additional cost for shipping them elsewhere.”

Some DIY enthusiasts have made imitations or approximations of the Polycrubs, but Drew points out that these are not the real deal.

“We’ve trademarked the name and the details of how we construct them is copyright. As far as the Scottish crofting counties are concerned, we’re very hopeful that the Polycrub will be eligible for crofting grants quite soon. There’s nothing at all as robust as this available on the market. If these can withstand our Shetland winter gales, they can handle anything!”

Further details

Read more about Polycrubs at and follow Nortenergy on Facebook – Prices for kits range from £2,100 to £6,000 before construction on-site. Planning permission may be required in some settings, depending on local regulations.

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