"Huff as hard as you like - you can’t blow a straw house down"

Segue um artigo muito interessante publicado hoje no Times relativo a investigação sobre casas com paredes de fardos de palha. 

Créditos imagens : ModCell

Times Online, 20 de Maio 2010

Autor: Ben Webster, Environmental Editor

"Scientists have ruined the plot of a children’s fairytale by proving that straw houses do not necessarily blow down, even when subjected to an awful lot of huffing and puffing.
The first straw housing estate is being planned after tests showed that walls built of straw bales can be made strong enough to withstand hurricane-force winds. A two-storey straw house constructed at the University of Bath moved only 4mm (0.16in) when subjected to a force exceeding four tonnes, equivalent to 120mph winds.
Researchers pushed hydraulic jacks against the walls to simulate the wind speed. They concluded that even a three-storey straw house would be strong enough to survive the worst storms Britain is likely to experience. The house in the tests was made from prefabricated panels that consisted of wooden frames filled with straw bales and covered with lime render.
The heating bills for this type of straw house, which has walls almost half a metre thick, are 80 per cent lower than for modern homes made from bricks and breeze blocks. The carbon footprint from the construction and materials is also far lower because straw locks in carbon as it grows.

Pete Walker, director of the university’s Centre for Innovative Construction Materials, said there could be a net carbon reduction if transport emissions were avoided by purchasing straw from local farms. “We hope the data will help strengthen the case for the mainstream building industry switching to using more sustainable building materials like straw,” he said.

“It can be difficult to get a loan for a straw house because of the perception among some building societies that they are not as strong. But we have shown that the BaleHaus design is robust and suitable for the windiest places, though that doesn’t quite include building one on top of Snowdon as a replacement restaurant.”

Professor Walker said that the house had also passed fire tests, with the lime render preventing flames from reaching the straw for one and a half hours, well over the 30-minute minimum under safety regulations. The greatest risk to straw houses is from moisture, which can cause the straw to decay. The university is planning to test how the panels would cope with a flood this summer.

Professor Walker said that lime render was breathable and this should allow any moisture to escape. “If you get an inundation we don’t yet know if the straw dries out quickly enough before it starts decaying,” he said. “But even in the worst-case scenario, the straw could be replaced in a panel for only a few hundred pounds.”

He added that the homes should last more than 100 years if they remained occupied and any leaks were quickly repaired. In Nebraska there are several straw bale buildings dating from the early 20th century.
The BaleHaus design used by the university requires eight panels for each storey. Once the concrete foundations are in place, it can be assembled in four days, compared with a minimum of four weeks for a conventional home.
An affordable housing co-operative in Leeds is planning to submit an application within three months for 20 straw homes in the Kirkstall area of the city. A single-storey apartment will cost £60,000 and a four-bedroom terrace home £160,000.
The homes will have slightly smaller rooms than conventional houses of similar overall dimensions. The straw bales are 490mm thick, compared with 300-350mm walls in a new brick home.
Professor Walker said: “This is an issue for developers that want to pack as many houses as they can into a space.” But he added that developers using straw would find it much easier to meet the Government’s target to make all new homes “zero carbon” from 2016. "

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