Posts Tagged ‘straw bale homes’

Canada’s Greenest Home to be Built in Peterborough

March 22nd, 2012

Endeavour Centre's next sustainable house, Peterborough, ON

The Endeavour Centre located in Peterborough, ON is a not-for-profit hands-on education centre that teaches students how to build and renovate homes using more sustainable methods and materials than are currently in use. Students learn about building science in the classroom, then take their knowledge onto a building site to apply it.

The people at the Endeavour Centre will build, starting in April, 2012, what they consider to be “Canada’s Greenest Home.” It is being built to surpass LEED Platinum standards, striving instead for the Living Building Challenge certification. This is a recent green designation that is by far the toughest green building standard to achieve. The Living Building Challenge strives for buildings to be, among other things, net zero water and net zero energy use, as well as being constructed using materials with the least embodied energy possible that are healthy, ethical, accessible, sourced as locally as possible and beautiful. The Living Building Challenge certification makes achieving LEED Platinum look like a walk in the park!

To achieve Living Building Challenge certification Chris Magwood, Director of the Endeavour Centre, and his crew are already hard at work sourcing local materials with low embodied energy. Part of this will include prefab walls that consist of straw bales for insulation. While straw bale homes aren’t new, even if they’re not that common, assembling them as a pre-fab structure certainly is. These straw bale walls are built near Peterborough by NatureBuilt Walls, so not only do they provide excellent insulation levels, they are also of very low embodied energy and don’t have to travel a long distance to get to the site. According to the information on the Endeavour Centre’s website, straw bale prefab walls provide an R value between 30 and 40 and are inexpensive to make, mould and mildew resistant, strong, and surprisingly (to me, anyway) are quite resistant to fire. To learn more about straw bale prefab walls, see this presentation.

In addition to pre-fab straw bale walls, the house will include grid-tied solar electricity, composting toilets, an underground rainwater cistern for rainwater harvesting, solar hot water, and natural paints and finishes.

The house will be put up for sale, and the proceeds help off-set tuition costs. The home will be priced affordably, demonstrating that an energy-efficient, state of the art home doesn’t have to be expensive. The house will be built over the course of five months, and at the end, the students completing the program will receive a certificate for their efforts. The point of the program is to give student hands-on green building experience and technical knowledge.

I was curious about how this house would be built and the challenges it will face, so I contacted Chris and asked him a few questions about it.

Cathy:  What will the heating method be?

Chris: We have been intending to use the Mitsubishi Zuba air source heat pump. It is rated to -30C and I’ve heard good things about it from those who have been using it. With the Living Building Challenge, we are basically limited to solar heating and/or heat pumps, as they disqualify any kind of combustion heating, including biomass (which would have been one of our options).

Cathy: What do you envision the overall kWh/sq foot will be? (similar or less than passive house)?

Chris: The PHPP (Passive House’s modeling software) has us at 80% more efficient than code, and their target is 90%. However, we modeled the building in a few different configurations, and found that we needed to nearly double the insulation levels everywhere to move from the 80% to the 90% figure. So we will not be pursuing Passive House certification, as we just can’t justify the additional costs and material use to get to PH levels. We’re very happy with the performance level the model is showing, and feel that we’re in the “sweet spot” where affordable, sustainable materials can be used to make extremely energy efficient buildings.

Cathy: Given the criteria of LBC [Living Building Challenge], how do you anticipate selling it to a buyer who will have to live by strict electricity use? How do you size a solar system to meet that use when you’re not sure what it will be?

Chris: There was a really interesting article in Green Building Advisor recently that looked at the whole notion of designing for net zero, and used two case studies… one in which the occupants used only 36% of the expected energy and another where they were 200+%. The truth is, we don’t know how the owners will behave and we can only design according to accepted averages and see what happens. I’m really not that concerned about getting certified with the LBC. I think it’s a wonderful standard and we’re going to work hard and do our best to meet it, but we can’t control things like the owner’s behaviour or the weather. It would have been easy to hit net zero if this past winter had been our “trial year” but that won’t necessarily be the case next year!
This isn’t the same article, but same message… http://www.buildinggreen.com/auth/article.cfm/2011/8/30/Want-a-Net-Zero-Home-Be-a-Net-Zero-Family/

Cathy: What will the overall R value be? R 30-40 for the walls, however roofing and basement will be what?

Chris: We’re rating the bale walls at R-30. I believe we’ll see better performance in real life, but that’s at the low end of the test results and that’s what the energy modeler wanted to use. However, because there are no thermal bridges at all (which PHPP calculates in every case), the results were good. We are doing some frame wall sections (to show the students two kinds of wall construction) and they are R-40. We’re doing R-28 Durisol block in the basement and R-80 cellulose in the attic.

Cathy: What kind of landscaping do you plan on including? An edible garden? Shading for summer heat? Green roof of some kind?

Chris: Definitely an edible garden (or the space to make one, since we won’t be planting it during the building season!), fruit trees (learning lots about the service berry tree lately) and all native and drought resistant plantings. There is passive solar shading for both stories on the south side (the skirt roof will hold the thermal collectors). No green roof… I’m not convinced they are a worthwhile investment for single family residences.

Cathy: When do you anticipate it will be ready for market?

Chris: October [2012].

For more information on the Endeavour Centre and sustainable building programs, visit its website.

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