June 9th, 2009 – BELLEVILLE, Canada – He’s no expert on the Canadian scene, but a UK civil engineer says that with strong buy-in from the British government, the UK will see an increase in the use of crop-based building materials as it works to reduce its carbon emissions.
Professor Peter Walker, a director and researcher at Bath University’s building research centre for innovative construction materials, says both straw and hemp-based building materials, won’t go mainstream anytime soon, but they are gaining ground.
“I don’t see them as a universal panacea, but a significant portion (of new buildings) will use those materials.”
He said the UK’s construction industry is responsible for about 10 per cent of its greenhouse gas emissions, with new and existing buildings contributing about half of the UK’s footprint; one third of that coming from the housing sector.
“The recession has hit the construction industry, but green building has held up or slightly grown,” he said.
Walker visited central Ontario recently, speaking at a meeting of the Eastern Lake Ontario Regional Innovation Network. He also toured a Sir Sandford Fleming College sustainable building site.
With support from the government, including a code for sustainable homes which aims to reduce carbon emissions from new homes by 90 per cent by 2016, there’s huge potential for buildings using renewable resources.
The use of renewable materials, Walker said opens up competition for agricultural markets, reduces the depletion of non-renewables and has proven to offer high levels of thermal insulation, with hemp-lime and straw bale structures actually storing, rather than emitting carbon.
“The farm can replace the quarry as a source of material,” Walker said, describing straw as a “very low carbon plant-based material.”
And there’s room for a “definite skill set” to specialize in the construction of such buildings.
“To me we have been de-skilling the industry; bricklayers and carpenters are not valued,” Walker said, adding there is a need for tradesmen with “artisan skills.”
An “experienced tradesman,” could learn it in no time.
Walker said the sustainable building industry is still fighting for acceptance, even though straw houses built in the 1800s are still standing.
“It’s a challenge at times trying to persuade people it will work.”
A civil engineer, Walker has been experimenting with advanced fibre composites and low carbon and renewable construction materials such as hemp-lime, straw bales and earth and timber construction. He has also experimented with pre-fabricated straw bale panels, though the later presents “handling issues.”
The rainy UK climate, is a challenge, he admitted, explaining the bales do have to be kept dry.
But a 32 mm lime mix render is sufficient to prevent decay.
He also noted that straw bale panels tend to have a 12 hour lag time in thermal performance.
Professor Walker has also experimented with hemp construction and explained that it can be either cast or sprayed in construction. Mixed on-site at a ratio of one part hemp to 2.25 parts lime to 3 parts water, hemp must be monitored to assure that it doesn’t dry too rapidly.
Hemp and straw demonstrated fire resistance properties which more then met building standards.
He noted that in one test, he raised the temperature to 900 degrees Celsius one side of a panel, and after one hour, the temperature on the other side of a bale panel was still 14 degrees Celsius.
But mainstream uptake is hindered by the usual culprits, he admitted.
While his research is on-going, there is still a limited understanding of material performance, a lack of design tools and materials such as hemp and straw bales still lack profile in mainstream construction.
Cost of a building using sustainable materials is about double that of traditional methods and with concerns over long-term durability, even though research is on-going, there is some “risk aversion.”
By Suzanne Atkinson – Source.