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First Straw Houses Hit the Market

Wednesday, February 11, 2015

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Despite their bad rap from the Big Bad Wolf, straw houses cannot be huffed and puffed and blown out of existence.

In fact, says Professor Pete Walker, straw is a warm, low-cost, safe, durable, biofriendly—and, yes, fire-safe and insurable—construction material. And he has the numbers to prove it.

Only time will tell if prospective buyers of his seven new straw townhouses in Bristol, England, agree.

PeteWalker
University of Bath

Professor Pete Walker has overseen research into straw bale construction for more than a decade. The work has included a prototype "BaleHaus" (behind him) at the University of Bath, where Walker heads the Department of Architecture & Civil Engineering.

"Fuel-efficient, affordable houses built using environmentally-friendly methods sound almost too good to be true, but our research has made it a reality," reports a research announcement from the University of Bath, where Walker has devoted 13 years of research into straw as a low-impact building material.

Third-Party Certification

Now, that work, which has included internal and third-party scientific monitoring and testing, has produced a straw bale panel, called the ModCell Core system, that has been certified by BM TRADA, a UK-based international certification body. BM TRADA has granted the system Q-Mark certification.

Professor Pete Walker discusses ModCell materials, which have received third-party certification.

In this case, the building products certification "guarantees a straw building’s energy efficiency, fire safety, durability and weather-resilience and means that developers and homebuyers can now get insurance and mortgages for straw homes and buildings," the university reports.

The Making of ModCell

ModCells are prefabricated panels that consist of a wooden structural frame infilled with straw bales or hemp and rendered with a breathable lime-based system, ventilated timber or brick cladding.

The technology has been developed by the university's Department of Architecture & Civil Engineering, which Walker chairs. The team has been studying the load-bearing capabilities of straw since 2005, when it began a collaboration with ModCell Ltd. to develop the straw bale cladding panels.

ModCell ModCell
ModCell ModCell
modcell.com

ModCell construction (clockwise from top left) involves prefabricated panels made of a wooden frame infilled with straw bales and rendered with a breathable lime-based system, ventilated timber or brick cladding.

Government funding and research recognition have followed, as has a prototype "BaleHaus" built and tested on the university's campus.

The researchers "carried out weatherproof testing in a very exposed site on the blustery Cornish coast as well as in the lab," the university says. "The ModCell panels have been blasted by simulated hurricane-force wind loads, soaked in water to simulate flooding, and exposed to roaring fires."

With all of that punishment came energy efficiency testing, which showed an energy usage reduction of "up to 90 percent" when compared with other homes.

Other Projects

The ModCell technology is already moving beyond the residential sector, with one local school testing the panels as a roof and using them as teaching aids, the team says.

ThermalImaging
University of Bath

Thermal imaging shows the insulation difference between the straw BaleHaus (left) and a typical home (right).

In addition to their naturally low-carbon materials footprint, the panels can be put together within 15 miles of a construction site at mobile factories, says the university.

The school is also expanding its sustainable construction efforts with the opening of a Building Research Park in Swindon for the testing of low-carbon construction materials and systems in open-air conditions.

The park includes a £1 million building project called The HIVE, which will support research into hygrothermal performance, flooding and construction loads.

 

   

Tagged categories: Bio-based materials; Building envelope; Building materials; Certifications and standards; Energy efficiency; Green building; Insulation; Renewable raw materials; Residential Construction

Comment from Jeff Laikind, (2/11/2015, 9:28 AM)

How thick are the walls of the straw house? And how well insulated is the "typical" home in the image? It would be interesting to see what the R value is for straw, in comparison to synthetic insulation (fiberglass, polystyrene, polyurethane, etc.).


Comment from Shyamala Rajagopalan, (2/11/2015, 11:08 AM)

How about allergies, air quality in the house, and the smell in the air?


Comment from Tom Schwerdt, (2/12/2015, 8:16 AM)

Jeff - the walls look 4x-5x as thick as conventional walls. Thick enough that you can hardly see the thermal bridging through the studs. Thick enough that the choice of insulating material becomes pretty irrelevant, except possibly for air infiltration. Going with a conventional wall thickness, dense packed cellulose between the studs and 1" of rigid foam sheathing on the outside should get you the same performance at half the cost, with the bonus of being much closer to conventional construction. Shyamala - why would you think of allergies, air quality and smell? It's not like you will have open bales of straw shedding into your house - the insulation will be behind drywall.


Comment from M. Halliwell, (2/12/2015, 10:49 AM)

Jeff, we've got a few structures up here where I live that are straw construction (not prefab panels like this, but conventional build with straw bale insulation). If my memory serves (it has been a few years since the article ran in the local paper), the walls were about 1 ft thick (plus sheeting), instead of the typical 4" + sheeting...so the core of the wall was about 3x the depth with the bales put in on edge. From the pictures, it looks like they are building the walls in the UK on the flat, so I would suspect Tom is right...the pre fab panels shown are probably 5-6x the thickness. Shyamala, unless you have a significant water / moisture problem, there shouldn't be issues with allergies, air quality or smells associated with straw.


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