There's a bite of October chill, but the crackling fire creates warmth.

The air smells like burning wood.

Sam Chillaron and Sara Henry use their hands to push crumbling red clay through a quarter-inch screen, sifting it to remove rocks and particles.

Karen Rudolph of the Sequatchie Valley Institute supervises.

Rudolph, along with Chris Gilligan, is teaching a three-weekend series on wattle and daub, a low-impact, sustainable building technique. This morning is the first workshop, at Rudolph's home.

Rudolph -- Gilligan calls her Rudy -- offers coffee to Chillaron and Henry. They are the only two students on this first morning, but more students are expected for the afternoon session. The couple, in town from Gainesville, Fla., to visit friends, extended their visit to Chattanooga because they wanted to attend the workshop.

"We wanted to see what was appropriate for the bioregion," says Chillaron. He and Henry have worked on several homesteads and were interested in learning the methods of wattle and daub.

A small structure, house-like in shape, stands in her backyard. The frame, created by timber, stands firm. The walls have yet to be installed.

The clay particles Chillaron and Henry are sifting will be mixed with chopped straw, sand and water to create a thick, concrete-like material, which eventually will be spread over a bamboo latticework

created within the timber-frame structure to create walls.

Gilligan uses a special tool to split stalks of bamboo.

"The clay in this area is great," he said.

Chattanooga, he said, boasts plentiful red clay that can be dug up from several inches below the ground. The clay is sifted through multiple screens, increasingly smaller, to create a fine red powder.

Very fine sifting, Gilligan said, can create a material that is more appropriate for indoor walls, which can be painted like plaster.

The mixture of sifted clay, sand, water and straw is a versatile combination that Rudolph and Gilligan said can be used for a simple mortar or to build a garden wall, as well as home structures, or even larger buildings.

The straw, which is chopped into pieces, forms a matrix, he said, similar to reinforcement bars (rebar) in concrete. The thickness of the walls can determine how well insulated a structure will ultimately be.

"It's a very interesting, natural low-energy technique," Gilligan said.