Rice, straw and coconut the new alternatives to wood

Paddy field

You've found the house of your dreams.

Or it will be when the renovations are done. After years of grotty flats and poky "starter homes" that ended up being second and third homes too, that windfall from great-aunt Annie is going to be put to good use.

More than anything you want to have some beautiful timber features both inside and out - but without destroying a small corner of the Amazon basin to do it.

Would your next thought be rice? Possibly not.

Swelling and splintering

Resysta may look like wood, and be used like wood, but the main ingredient is rice husks.

"The idea was to create a new environmentally friendly material that could replace a variety of natural building materials, like stone and in particular tropical hardwood, for all uses where water creates difficulties," says Bernd Duna, managing director of Resysta International GmbH.

"Demand for wood such as teak has boomed in recent decades, making it into a profitable export, yet the long growth cycle of hardwood trees and the difficulty of certifying origin has meant the de facto existence of a large unregulated 'grey market' that preys on mature forests."

Image caption Resysta being used in a Hong Kong park

The husks are powdered, mixed with salt and mineral oil and pressed into board. Mr Duna says the material looks like tropical hardwood, but has certain advantages.

"It cannot absorb water, which causes wood to swell, warp and splinter.

"Secondly, wood contains a compound called lignin which leads to greying - but as rice husks are mainly cellulose, they do not have this compound and so the material maintains its original appearance."

The recyclable material has won awards for its sustainability credentials - using a widely available agricultural by-product to conserve hardwood stocks.

Resysta is more expensive than more traditional alternatives, and is designed for exterior use. The company will also recycle it at the end of its usefulness.

Jörg Sperling is a partner at clean-tech private equity firm WHEB Partners, which has invested heavily in the business.

"There's a lot of interest in sustainable building. You have large operators of hotels or shopping malls, supermarkets - they want to give their properties a green look.

"Consumer awareness is driving this. People are looking for viable alternatives to wood where you have the green credentials, but still you have material that's easy to maintain."

Straw houses

Image caption Kirei board is made from sorghum straw

Straw as a building material may have a bad reputation among pigs, but a California company has developed a technology to challenge that assumption.

Kirei board is made from sorghum stalks, another renewable agricultural by-product that would otherwise be burnt or make its way to landfill.

This is a material designed for its aesthetic appeal - kirei is Japanese for beautiful - with customers globally including Starbucks, McDonald's, Hilton and Google.

"Green has to be beautiful," says company founder John Stein.

"If you're going to do green for green's sake you're going to have a very limited market - people who have health issues or people with a conscience.

"If you have beautiful materials that happen to be green, then really they're open to everybody. I regard it almost as a gateway drug to other green activities."

Image caption Kirei USA's John Stein says that "green has to be beautiful"

Currently, the board is produced at the company's plant in Asia, but there are plans to expand production to other areas of the world.

A no-added-urea formaldehyde adhesive is used, with bio-based binding agents in the pipeline.

"I think there's a large potential for new materials being developed every day using what were once considered to be agricultural waste products.

"We're reclaiming them, and turning them into valuable building materials."

In terms of cost, Mr Stein says it is comparable to mid-range hardwoods. The company also produces a wheat-based MDF alternative, hemp panels, coconut mosaic tile, and a range of bamboo products.

Illegal harvesting

Using hardwoods of course isn't necessarily a bad thing.

"The whole problem is with tropical hardwoods," says Andrew Lawrence, timber specialist at Arup, a founding member of the UK Green Building Council.

"Those are the ones where there's a general problem with a lot of unsustainable, illegal harvesting."

Image caption Tropical hardwood being offloaded in Indonesia

His colleague Dr Kristian Steele, senior consultant specialising in materials and sustainability, agrees.

"Temperate hardwoods [such as beech and oak, found in North America and Europe] represent much less of a problem.

"To use it isn't fundamentally wrong, you just need to use it in the right way, and ensure your procurement processes are proper in terms of where you're supplying and purchasing from."

In general, softwoods grow faster than hardwoods, which means that they can be harvested earlier, and are rapidly replaced.

There are always exceptions - eucalyptus is a hardwood, yet has a growth cycle of just 20-30 years.

Deforestation of the rainforest areas where many hardwood species grow has been linked to climate change and has a devastating impact on bio-diversity and the water cycle.

Across the developed world businesses are being forced to consider sustainability, as governments try to clamp down on the use of unsustainable tropical hardwoods.

Choosing FSC-certified (Forest Stewardship Council) wood means it has been sustainably sourced.

Assessing your green building material can be a complicated balancing act.

"When we talk about sustainability of materials, we want to look at the impacts and the benefits.

"There might be a whole host of criteria that frame impacts and benefits.

"So you end up with quite a complex set of parameters against which you're judging materials, and that may change depending on what it's being used for."

Conker champion

Image caption The pine goes into the reactor for acetylation at Accsys Arnhem plant

Softwoods such as pine are traditionally less stable, less durable and more prone to bleaching than their more stoic sisters.

Put them through a process known as acetylation, however, and that could change everything.

Chief executive of AIM-listed Accsys Technologies Paul Clegg explains how it works: "I don't know if you've ever played conkers, but in order to make your conker harder you would soak it in vinegar and stick it in the oven.

"In essence what you do there is acetylate the conker. You make it harder and you make it much more stable."

Radiata pine is loaded into one of two reactors at the company's plant in Arnhem in the Netherlands.

A vacuum is created and then flooded with a liquid called acetic anhydride - effectively industrial vinegar - which is sucked into the spaces in the wood.

Image caption Chemistry lesson: How acetylation works

It is heated to start the reaction, and when it is complete the resins, residual acetic anhydride and acetic acid are wicked away from the wood, and the pine has become Accoya.

The result, says Mr Clegg, is a material that has the look and feel of hardwood, but that is stronger, more stable, durable and longer-lasting.

"What we don't know is whether it ever rots.

"We know it lasts for 50 years above ground. You can burn it, chip it and recycle it so it doesn't become a problem, but it's an 'at least' number not a maximum," Mr Clegg says.

An independent report carried out by research institute Scion found Accoya was more durable than the most durable hardwoods.

Image caption This bridge in the Netherlands city of Sneek is made of Accoya

The company has had ups and downs in recent years. Mr Clegg joined in 2009, and the business now has a new board, management team and structure.

Accoya is used around the world, from a velodrome in Tbilisi, to decking on the Shanghai Bund and Disney theme parks. The company hopes to license the technology to others, and is working on Tricoya, an acetylated MDF that can be left outdoors untreated, unlike regular MDF.

"We've gone beyond the tipping point," Mr Clegg says.

"Sustainability or responsible behaviour amongst consumers or corporations is becoming ingrained in society."

Arup's Dr Kristian Steele feels business now has little choice in the matter.

"The reason business should be specifying sustainable materials is not that it's just ethically the right thing to do, but for commercial longevity it's going to be the right thing to do as well," he says.

Related Internet links

The BBC is not responsible for the content of external Internet sites