Straw Bales & Solar Energy -- A Natural Partnership

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Straw bale walls can be part of a whole-house plan to achieve high energy efficiency while keeping embodied energy low.
In a post-and-beam structure, bales are notched around the structural uprights, preventing thermal bridging. (See "Straw Bale Walls" sidebar.)
In an I-joist structure, bales are fit between the joists, which reduces thermal bridging compared to a conventionally framed structure. (See "Straw Bale Walls" sidebar.)
A bale wall will rest on a raised and insulated double sill.
Author and builder Rebecca Tasker (center) helps homeowners ceremonially set the first bale.
Exterior stucco can be lime-cement or, for reduced embodied energy, earthen-based, and any plaster used must be vapor-permeable.
Bale wall systems have fewer thermal bridges that cause heat flow across the assembly.
Well-sized roof overhangs protect the walls, and shade south-facing walls and windows from the intense summer sun. (See "Southern (Oregon) Comfort in a Solar Straw Bale Home" sidebar.)
A double airlock entry reduces air exchanges by stopping blow-through when the outer door is opened. (See "Southern (Oregon) Comfort in a Solar Straw Bale Home" sidebar.)
Clerestory windows let in natural light and admit solar heat during winter. (See "Southern (Oregon) Comfort in a Solar Straw Bale Home" sidebar.)
Thick walls make deep windowsills, for an old-world feel. (See "Southern (Oregon) Comfort in a Solar Straw Bale Home" sidebar.)
High ceilings paired with well-placed windows promote convective cooling. (See "Southern (Oregon) Comfort in a Solar Straw Bale Home" sidebar.)
A natural earthen floor covers R-15 insulation and provides thermal mass for storing passive solar gain. (See "Southern (Oregon) Comfort in a Solar Straw Bale Home" sidebar.)
Multiple layers of natural plaster, both interior and exterior, mitigate diurnal temperature swings inside the building.
Thick walls make for deep door and window openings. There are several structural and aesthetic ways to approach this.
Thick walls make for deep door and window openings. There are several structural and aesthetic ways to approach this.
The relatively simple, but labor-intensive, aspect of building with bales fosters community involvement with “bale raising” parties.

Building with straw can completely change how we use resources in construction, how we heat and cool our homes, and how we relate to the buildings we inhabit.

Straw bale building has unique and important answers to a few broad questions that help us get to the heart of sustainable building:

•           What materials will have the lowest environmental impacts during and after construction?
•           What materials and techniques will result in the most effective building—one that is durable, efficient, safe, healthy, and comfortable?
•           What materials can be used together to make a building appealing over generations because of its resonant beauty, sense of solid shelter, and peaceful comfort?

Low-Impact Building

The straw in bales is left over from grain harvesting. Crops aren’t grown just to make straw bales: the plants are being grown for rice, wheat, barley, or oats. Once the grain is harvested, the stalks are bundled together into bales.

Straw is an abundant agricultural by-product with few uses, and using straw bales as a building material is a great example of upcycling. Unlike wood, straw is an annual crop and can often be sourced locally—frequently from less than 100 miles from a building site. That results in a small carbon footprint: other than the energy it takes to bale the leftover stalks and then deliver that bale to your job site, all of the other resources needed to produce that bale were used for the production of food.

The California Straw Building Association (CASBA) is currently studying how much carbon a straw bale wall sequesters. Plants draw carbon out of the air as they grow and lock it up, releasing it only when they decompose (or burn, which is what happens to many grain fields when the straw is not upcycled). By keeping the straw in the wall, the carbon is not released into the atmosphere (see “Carbon Sequestration” sidebar).

Plastered straw bales replace the insulation and drywall, and often the paint. They can reduce the amount of lumber needed for framing, and may even be part of the structure. Leftover straw can be used as fiber in the plaster, or used onsite as mulch without further processing. And at the end of a long life in a straw bale building, a straw bale is biodegradable.

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