Episode Four: Straw Bales

Straw Bale Basics

"Today we're working with our main ingredients: straw bales. Imagine, a farmer's waste material stacked and plastered to become structure and insulation as one. And where straw bales are not appropriate, we're using a new product that is not your father's insulation. It's more like your baby's blanket and your favorite pair of blue jeans."

- Building Green Host Kevin Contreras

Straw is the stalk of threshed grain. It has little nutritional value and is usually bundled into bales to be used as bedding for animals and for erosion control. But Kevin has a different plan: He is going to use straw bales as the building blocks for his new home. Using straw bales for home construction is a good green choice because straw is a renewable, natural building material; it is highly insulating and, therefore, very energy-efficient.

Kevin's first step is to find dry, structurally sound straw bales, transport them and then move them to the center of the house so that they don't get wet.

Building with Straw

Kevin visits Dave Exline of the Three Little Pigs Construction Company, who specializes in straw bale building. Dave is in the process of building a new straw bale home in Paso Robles, California, where temperatures are soaring into the 100s. This is the perfect opportunity to learn more about the process.

First Dave shows Kevin how to inset windows by building a window "buck." Next, Dave explains how easily a window seat can be constructed with straw bales and then discusses the organic shapes the bales give to a home. Dave also shows Kevin how to install electrical wiring within the straw bale walls using a Romex, a type of plastic insulated wire. On a more aesthetic note, Dave also shows Kevin how to create architectural accents within the straw bale construction.

Dave and Kevin wander outside to discuss the insulating capabilities of straw bales. "They're super insulated packages," explains Dave, "and so when it can be 110, 112, outside, it doesn't affect the temperature on the inside, because we have such an insulation barrier. The mass on the outside, the stucco on the outside, it will build up a certain amount of temperature. And it will get 118, 120 on the outside surface, but it can't penetrate the house."

Every bit of Dave's advice is invaluable, and Kevin returns a month later to see the house after it has been plastered.

Straw Advantages

Did you know that a regular wall is 90 percent air? Because of all that air, when fire gets into a standard wall it burns quickly and races right up it. A bale wall on the other hand, even if you chip away all the plaster and light it, will burn quickly for a second or two, but then the flame has nowhere to go. Because bales are so dense, there is not enough air for the fire to travel up the wall, making them highly fire resistant.

Straw bales also ensure a less toxic environment inside the home. As our Building Green health expert Alyssa Alvord explains, straw bales are breathable. Because water vapor can move in and out of straw bales, they reduce the chance of mold growing in the walls. Kevin explains that exposure to elevated levels of indoor mold infestation is a proven health threat.

Straw bale building is also cost-efficient. Kevin calculates that it will take approximately 600 straw bales to build his green dream home. The total cost comes to just $2,600. "Since the straw bales serve as both walls and insulation," explains Kevin, "that means that for roughly the same price as standard building insulation alone, we are able to use straw bales to insulate and provide basic wall structure for our home. Now, that's saving green."

It takes a little time, but Kevin finds a farmer in the central valley of California with rice bales that he is willing to guarantee will be clean and dry upon arrival in Santa Barbara. Once the straw bales arrive, installation begins. After a few walls are up, Kevin gets a visit from bale and plaster expert Tim Owen Kennedy. Tim explains that the only reason that the building community moved away from natural materials was because of their variability. "It's that variability, that's the spice of life," he explains. "I mean, you know, every time you make a dish, it's not exactly the same."

Kevin then decides to invite a few friends and neighbors over so that they can see the progress. They are amazed at how quiet and cool the house is, even though there are no windows or doors. It takes 20 days to finish the straw bale installation.

Blue Jean Insulation and Other Alternatives

Although straw bales are the primary form of insulation in the house, Kevin decides to use another green option to complete the home's envelope. Blue jean insulation holds more heat and absorbs more sound than the insulation commonly used in homes; it also eliminates formaldehyde and other harmful chemicals that outgas and cause irritation to the skin, nose and throat. Blue jean insulation is made from recycled denim trimmings from blue jean manufacturing factories, making it a great green choice.

Kevin takes a trip to Phoenix, Arizona to visit a blue jean insulation manufacturing company. There, Todd Kennedy walks Kevin through the entire assembly line and explains how they take scraps of blue jeans and turn them into insulation. Blue jean trimmings are mixed with a polymer fiber to bind them, then the mixture is ground up and sent to a secret, patented machine that adds a flame retardant and a mold and mildew inhibitor. Next, the mixture goes into a huge oven that melts the poly fiber to hold everything together. Lastly, it is cooled and cut to various widths. Kevin invites Todd back to his house to demonstrate proper installation. The blue jean insulation is used in between the floors and in the ceiling, as well as in the interior walls not made of straw bales. Kevin explains that in many places like California and other warm climates, insulation was not put in houses for many years.

A simple building green step that Kevin recommends is to climb up into your attic and install something like blue jean installation. While blue jean installation is very simple to install, Kevin also explores a more extreme green building technique: cob building. Cob is earth, sand and straw mixed together and massaged onto a foundation, creating thick, long-lasting, load-bearing walls. Furniture, alcoves and shelves can be sculpted and carved out as you build.

Next week on Building Green: doors and windows.