Straw houses touted to unlock big gains
Every tonne of grain produced in New Zealand yields the same weight in straw, according to the director of Nelson company Fineline Architecture.
Up to 40% of that straw was burnt every year, said Magdalena Garbarczyk, citing figures from the Foundation for Arable Research.
‘‘You see big fires in the Canterbury plains, because there is simply just not enough time to plough the [cut] straw back into the land, or to use it as animal feed or for any other product.’’ Using straw differently – and more widely – to build homes in New Zealand would not only cut the harmful gases released by burning the crop residue but help keep the carbon it sequestered locked away, Garbarczyk said.
It would lead to homes that emitted less carbon, during construction and after, and that cost less to build and heat than houses typically built now, she said.
Key to the proposal, in a joint project with Unitec Institute of Technology researcher Min Hall, was building homes with prefabricated panels that contained straw.
Straw had ‘‘phenomenal’’ insulating properties, and was already used in the construction of some houses in Aotearoa, Garbarczyk said. But that was traditionally a ‘‘very long’’ process, which involved building a timber frame, using straw as an infill, and plastering it on both sides, the former lecturer from Unitec’s school of architecture said. Using timber panels, with the straw already encased inside, required less labour – ‘‘the highest cost in construction’’.
The prefabricated straw and timber panels could be assembled ‘‘a little bit like Lego blocks’’.
The panels in the ‘‘Strawlines’’ project had a thermal resistance level three times higher than required in the Building Code, significantly reducing the energy – and money – needed to heat homes, Garbarczyk said.
Straw sequestered carbon ‘‘in quite big quantities’’, which was then locked away within a building made with the panels, for the lifetime of the building, she said.
But the material was nothing without the design, she said.
‘‘If you use those panels to build a 350-square-metre house, we are not really solving anything.
‘‘We are using the material in homes that are very small.’’
The project proposed one to three-bedroom houses, which had a total area of 45-75 square metres.
They incorporated built-in furniture, mezzanines and double height spaces which created a feeling of spaciousness, and made them warm and energy efficient, Garbarczyk said.
Elements like roof cassettes could be assembled offsite, eliminating the need for extra structures to support the roof, she said.
‘‘When you have assembly lines that prefabricate elements of the house, the quality is usually superior, it is done a lot faster, it is a leaner process, with a lot less wastage, and it costs less because it . . . requires less people, less labour, less energy.’’
Prefabricated straw panels were being used more frequently in Europe on buildings of varying scales, she said.
Adapted to Aotearoa’s climate, rules and available materials, the project’s authors were now looking for developers to take on their designs.
The project has been shortlisted for an international design competition for ‘‘resilient and adaptable houses’’.
* Garbarczyk is due to speak at a climate leaders event at the Mahitahi Colab on the NMIT campus in Nelson on Tuesday, marking a year of the programme run by Mission Zero, an initiative from local charitable trust Businesses for Climate Action.