Sips from bottles and leaves

Ever since I first heard about them maybe ten years ago, I’ve been a huge fan of Structural Insulated Panels (SIPs) as a building system for energy efficient buildings. I’ve never quite understood why SIPs hasn’t been picked in the Australian market in a much bigger way than it has. Whilst things are improving, market adoption of SIPs has remained modest and limited to just a few specialist players.

Recently, two completely unrelated events caused me to think about SIPs again. Firstly, for my 50th birthday my lovely partner Frances took me on a bucket-list holiday to the Maldives. Secondly, one of our neighbours has expressed concern about leaves dropping over the fence from our poolside bamboo grove. “What on earth could a tropical resort holiday and a neighbourly issue with falling leaves have to do with SIPs?”, I hear you wonder. Before I get into that, let’s briefly recap on what a SIP is and how it works.

A SIP is constructed like a sandwhich, with the “bread” generally being two sheets of structural ply or Oriented Strand Board (OSB), and the “filling” being an insulating foam material such as EPS, XPS, PIR or PUR. The three layers are bonded together with a glue under pressure, to produce an extremely strong, lightweight panel capable of performing as a combined structural element and insulation layer. Hence, Structural Insulated Panel.

By combining functions, SIPs panels can speed construction. Indeed, they are often pre-cut offsite based on the building plans, and delivered as a flat-pack where they can be rapidly laid out and nailed together. With SIPs, it is possible to achieve lockup in a typical house-sized building in a matter of a few days.

OK, so what of the Maldives and bamboo?

Well, the Maldives is indeed a remote, beautiful place. It was quite a journey to get there, flying from Melbourne to Singapore, then on to Mali, followed by a short speedboat trip to our island. The water is crystal clear, warm and blue. There is a lot of dead coral, but snorkelling along the drop-off is a spectacular experience with sharks, eagle rays, turtles, and millions of fish in every colour imaginable. And plastic bottles bobbing around in the water everywhere. Our resort had a strict ‘no plastics’ policy, so no straws and no plastic drink bottles, which was terrific to see. Yet sadly, bottles, plastic bags and sheet, and other items drifted in the waters around the islands in their thousands.

At about the same time, news reports of China starting to refuse to take Australia’s recycling waste were starting to emerge. And so it got me thinking about what could be done with all this plastic – not just that I could see floating around in Maldivian paradise, but building up relentlessly in oceans and landfills around the world. Of course, Polyethylene terephthalate (PET) bottles are routinely recycled today into all sorts of things. But being a sustainability nerd, I wondered whether this material could be recycled into something much more wonderful – insulation! It seemed like a reasonable idea, to turn waste PET bottles into fibre or foam. And so to Google, where I learned that there is a company called Armacell in Belgium doing just this! My purpose here is not to advertise them specifically, just to note that there is at least someone out there turning PET bottles into green foam core products. There may well be others who didn’t stand out so readily in my searches. In any case, the Armacell products I found appear to be fully recycled, and they have a fire-resistant version. The boards come in a variety of thicknesses, up to 320mm. The 200mm board has a λ-value of 0.043 W/mK, giving a U-value of 0.043 / 0.2 = 0.215 w/m²K. This is a great starting point for a Passivhaus built in Melbourne’s warm-temperate climate zone – although I’d agree it makes for a fairly chunky wall!

Meanwhile, in our backyard a small grove of bamboos were dropping leaves, probably as a result of the dry Summer in Melbourne this year. After getting some complaints from a neighbour, I again turned to Mr. Google to find out what we could do. Do you get the feeling I resort to Google a lot? Anyway, amongst reading about root barriers and pruning, I also learned that bamboo:

  • Is amongst the fastest-growing plants in the world
  • Release 35% more oxygen than trees
  • Can be harvested in less than 5 years, compared with up to 20 years for softwoods
  • Creates 6x more biomass than pine trees
  • Is one of the strongest building materials available, and with a tensile strength of 28000 psi is stronger than mild steel

I could go on, but I think you get the point. Miracle plant, but not necessarily a hit with the neighbours. Anyway, the properties of bamboo got me wondering whether it would be any good as the raw material for OSB. Again, Google to the rescue, and this time I learned that bamboo OSB is a new but growing industry in China (which happens to have more bamboo than anywhere else). Apparently mould grows quite well on bamboo, so it would need to be treated. But again, Google pointed me to some research studies showing the effectiveness of copper-aqueous pre-treatments for preventing mould growth in bamboo OSB.

So there you have it! SIPs are an awesome solution for construction of highly-insulated buildings, and a SIP made from recycled bottles and plantation bamboo would have to be a winner, surely. What do you think, am I onto something? I’d seriously love someone to start manufacturing such a product, and I would recommend it to all my clients. But if it does turn out to be a billion-dollar money-maker for you, I hope at least you’ll give me mates rates 😊

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