Building a High-Performance, Low-Carbon House

Intermediate

Inside this Article

A straw bale SIP starts with a structural form and a base layer of plaster.
The base plaster is spread and screeded to a thickness of 1 inch.
Bales are individually “buttered” to adhere to the plaster layer.
Bales are squeezed into the form, butter side down.
A top coat of plaster is worked into bales and spread to 1 inch.
The finished surface is screeded and smoothed.
Sustainable New Construction students with the finished bale SIP. After drying, the panels are transported to the building site.
Finished bale SIPs can weigh between 800 and 2,000 pounds and require a crane for moving and placement.
Straw bale SIPs are commonly 4 by 8 feet, but can be custom-sized to fit the envelope design.
A stem wall of Durisol insulated concrete blocks made from waste wood chips and cement offers lower embodied energy and more sequestered carbon.
Poraver expanded glass bead aggregate provides subfloor insulation without the embodied carbon of polystyrene.
Poraver expanded glass bead aggregate provides subfloor insulation without the embodied carbon of polystyrene.
Two Thermo Dynamics solar collectors provide all the hot water needed during three seasons.
An EcoSmart electric on-demand heater provides winter backup.
Careful air sealing provides 0.6 ACH, meeting Passive House standards.
Even with a narrow south profile, the house is optimized for passive solar gain with adequate glazing and overhangs.
A 5,082 W rooftop PV array and a Kaco Blue Planet inverter make a grid-tied system that provides about 70% of yearly energy loads, but still creates a net profit due to the Micro FIT payments for PV-generated energy.
A 5,082 W rooftop PV array and a Kaco Blue Planet inverter make a grid-tied system that provides about 70% of yearly energy loads, but still creates a net profit due to the Micro FIT payments for PV-generated energy.
An induction range cooks using electricity—without wasting heat.
Custom-blended clay plasters, and clay and lime paints are some of the natural, nontoxic materials that were used throughout construction.

When it comes to reducing emissions that contribute to climate change, the combination of renewable energy and natural building materials offers an affordable, achievable, and effective solution.

Reducing construction industry greenhouse gas emissions has focused on the energy efficiency of buildings, by reducing the energy used to heat, cool, and power each building. This focus makes sense, as the energy-related emissions over decades of building use are an obvious target.

However, two critical factors are often overlooked: the emissions of the energy source and the embodied emissions in the building materials—from raw materials extraction to manufacturing. Unlike “fuzzy” targets for energy efficiency—which depend on the quality of construction and occupant behavior for any degree of success—these are measurable factors that can be guaranteed to have the desired effect.

Using renewable energy has immediate and measurable impacts in offsetting carbon dioxide and other greenhouse gases. Less understood is the embodied carbon footprint of building materials, including construction materials intended to decrease energy use. Ironically, high-carbon-emitting materials are often used to save energy and carbon.

Consider the carbon footprint of different insulation materials (see “Materials” table), some of which have a very high carbon footprint. For example, a conventionally constructed, 2,000-square-foot house insulated with fiberglass batts in the walls to achieve R-28 will be responsible for 1,750 pounds of carbon emissions. The same house that uses extruded polystyrene foam insulation in the walls has a carbon tally more than double that, at 3,820 pounds. That home could have been built with straw bale walls, which have a carbon-sequestering effect and would have removed 4,245 pounds of carbon from the atmosphere—where it remains in the home’s walls.

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Comments (3)

Terry Trefz's picture

Would like to know how the SIP are joined together and It looks like there are viods all around the outside of the SIP.? How did you run electric and plumbing?

Temporary Username 1287's picture

I have done a few straw bale homes as a structural engineer, but remain unconvinced as to their suitability for northern prairies (we need more R value).
Also, I hate to say it, but the carbon emissions required to mobilize a crane and the extra folks to the site to do this work, will eat up the carbon sequestration. We like to use old newsprint in our walls, and leave the straw on the land for soil improvement.

BTR's picture

Great article. I'm curious how the (is it?) "life cycle energy" of this home compares to the two mentioned above. (code built home & the Passive House using foam insulation).

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