I met Ben Polley on the trip to Poland in October, 2014, but his company, Evolve Builders had been on my list of ones to contact for awhile. Evolve Builders builds low impact houses and buildings from straw, earth and wood. The company is divided into various divisions each of which specialize in a particular area of green building ranging from green design to “biological based building systems” (dealing with gray and black water and the like) through the Torus division.

mobEE, the prefabricated straw bale school portable system has recently signed a contract with the Pinoleville Pomo Nation to provide six mobEE units for the aboriginal group. What is unusual about this contract is that this nation is based in northern California. You might be wondering, like I did, why this group from northern California selected a southern  Ontario-based natural builder to build these school buildings for them. The questions was answered in Evolve’s press release:

After extended bid requests for a strawbale constructed portable school structure failed to garner interest locally or elsewhere across the U.S., determined Pinoleville Native American Head Start program representatives discovered Evolve’s mobEE eco-portables. Both parties came to learn that they held in common many organizational values, including support for local jobs, environmental stewardship, healthy buildings and energy efficiency. This inspired a joint effort that ultimately will meet Pinoleville Pomo Nation’s ideals, needs and budget.

Construction of the walls will take place in the Durham, Ontario factory then the parts will be shipped to California where they will be assembled by local trades, overseen by the mobEE group.

The structure:

mobEE, the acronym stands for “mobile Eco Enclosure”. The units are made from straw bales and finished with a sturdy reinforced cementitious plaster both on the interior and exterior — strong enough to stand up to children and Canadian weather. The floors and roof consist of structural insulated panels and the structure sits on a steel frame. The two sides of the building can also be moved and reattached in the same way that conventional portables are.

Straw Bale Truth Window
Straw Bale Truth Window

Customizeable: Evolve will work with a client to give them exactly the kind of portable they’re looking for. It can be sent to the site “turnkey” as in, completely outfitted with everything installed and assembled by Evolve, or, it can be “bare bones”  with just the building envelope, to be assembled and finished on site by a local crew – also used for teaching building skills to senior students. Regarding the heating and cooling system, depending on the requirement, a space outfitted with a protective sleeve is cut into the building to allow for whatever heating/cooling/ventilation system a school board requires.


Energy Efficiency: These units have been in operation in Ontario for five years. The first one was built for the Upper Grand District School Board. The building envelope is thick (straw bale walls), resulting in walls with an R value of 40, floor, R-29 and  roof, R-39.5. The result is a tight building envelope that needs little residual heat.Lighting provided is T-8 florescent tubes. To verify the energy efficiency of these units, any building operated within a public school board within Ontario must publish its energy consumption and greenhouse gas output annually. This mandate has allowed the mobEE builders to track its portables’ energy efficiency. The resulting energy savings are significant: almost six times better than the energy consumption of an average school building within the district, and 2.5-3 times better than the most recently built school, finished in 2013.

GHG Emissions (Kg)Energy Intensity (ekWh/sqft)
Average of all schools:148886.7819N/A
Avg of all schools /sq ft:2.8519.01690013
Island Lake/sq ft: 0.43 4.470685328Four to six times better than average
Next best school/sq ft (King George, Guelph):1.5310.74541288Two and a half to three times better than next best school
Worst school/sq ft (Wellington Centre for Continuing Ed.):4.9832.18370295Seven to eleven times better than the worst performing school

Note: “ekWh/ft2” where “e” stands for “equivalent.” Energy coming from different sources (ie., electricity or natural gas) has been converted to the same units for easier comparison.

Interior of the mobEE
Interior of the mobEE

Indoor Air Quality: One thing conventional school portables are known for is their staggeringly poor indoor air quality. Reports of black mould abound in conventional portables and it’s certainly one of the reasons parents (myself included), resist the use of portables when a school outgrows its space.  Poor indoor air quality has been known to contribute to illness in staff and students, with resulting respiratory problems being one of the main problems. Absenteeism rises, learning is diminished.

The mobEE creates a clean air environment for several reasons:

  • Breathable walls: the lime-cement based coating on the straw provides a large thermal mass which helps not only regulate temperature, but also humidity. The walls and straw bales are “hygroscopic” meaning “water loving” — so they absorb excess moisture in the air and release it when the air is dryer than the walls maintaining relatively constant and comfortable humidity.
  • mould resistant: the walls are mould resistant due to the nature of the straw and the cementitious covering and the lack of condensation build-up within the structure.
  • Flooring is anti-static no wax linoleum flooring providing easy maintenance and no need for wax or chemical cleaners to maintain.
  • Use of natural, low VOC and no-VOC finishes, ensuring that no off-gassing of harmful chemicals will occur.

Cost: To construct one of these portables costs less than a conventional portable with a service life at two to three times the service of a regular portable (projected 50 year service life), with lower maintenance and operating costs.

To follow the construction of the mobEE units for the Pinoleville Pomo nation like their Facebook page. To find out more about these portables, visit the mobEE website.

BEC Green

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