On a small lot tucked between conventional homes on Boise Avenue, Mark Lung is hard at work stacking bales of straw and mixing mud.

He is building a new home using local, recycled agricultural waste to form and insulate exterior walls. Plaster made from clay, sand, lime, straw and water will be used on both the interior and exterior instead of drywall, siding and paint.

Similar in appearance to Southwestern adobes, straw bale structures are earth-friendly and energy-efficient, Lung said.

Unlike the wall in a typical home, which is about 6 inches thick, a straw-bale wall is 18 to 23 inches thick, providing greater insulation against winter cold, summer heat and sound. Fire and pests are not a problem, advocates say, and straw is a cheap, easily renewable building material.

"Straw makes sense. It is the building material of the future," Lung said.

"The building industry is in a real revolution," said Lung's builder, Ron Hixson. Hixson's local company, Earthcraft, specializes in innovative, energy-efficient design and construction. With rising construction costs and a new economy, natural materials like straw are becoming more popular.

Green building "should reflect the earth itself," Lung said. His house does: straw, dirt and sun - his passive solar design will help heat and cool the house.

Lung lived in a straw-bale house in Gunnison, Colo., before moving to Boise. While there, he carefully charted the temperatures over an extended period. The outside temperature ranged from 20 to 80 degrees. Inside, the temperature stayed between 68 and 72 - without supplemental heat or cooling.

The cost of building a straw-bale home is comparable to a conventional home. The materials - straw, sand and clay - are cheaper. The labor is more intensive, and includes applying multiple layers of plaster to the straw walls.

To build his home, Lung purchased 250 bales at $2 a bale from a Meridian farmer. He held a "barn-raising" event to get his walls up.

Lung is providing much of the labor himself and is using recycled materials, which brought the costs down to about $86 a square foot - he's spending about $165,000, not including land.

Building the 1,900-square-foot home with conventional materials would have cost Lung about $103 per square foot.

Lung and Hixson are sharing their straw-bale building experience with other builders, architects and students.

They hosted a workshop last month; this month Timberline High School environmental science students will help apply a layer of "mud" to the house.

Lung said that almost every day, curious passers-by stop and ask about the house. Lung gives them a tour and explains what he is building and why.

Despite their positive attributes, straw-bale homes still haven't caught on with the mainstream in urban areas, primarily because city codes have not been updated to allow them, Hixson said.

Boise has one other straw bale structure that was built in 2000 - a 600-square-foot addition to a conventional home - said city planning director Hal Simmons.

The city decided then to implement a straw-bale policy. "That (permit) apparently took the owner almost two years to get approved," Simmons said.

Cynthia Sewell: 377-6428