Taking small trees from a crowded stand in the forest is much like thinning carrots in a row: the remaining plants get more light, air and nutrients. Carrots grow longer and straighter; trees get bigger and healthier.

Image The loft in the Stoddard, Wisc. home of Amelia Baxter and Mr. Gundersen. Credit... Paul Kelley for The New York Times

And when the trees are left whole, they sequester carbon. “For every ton of wood, a ton and a half of carbon dioxide is locked up,” he said, whereas producing a ton of steel releases two to five tons of carbon. So the more whole wood is used in place of steel, the less carbon is pumped into the air.

These passive solar structures also need very little or no supplemental heat.

Tom Spaulding, the executive director of Angelic Organics Learning Center, near Rockford, Ill., northwest of Chicago, knows about this because he commissioned Mr. Gundersen to build a 1,600-square-foot training center in 2003. He said: “In the middle of winter, on a 20-below day, we’re in shorts, with the windows and doors open. And we don’t burn a bit of petroleum.”

“It’s eminently more frugal and sustainable than milling trees,” he added. “These are weed trees, so when you take them out, you improve the forest stand and get a building out of it. You haven’t stripped an entire hillside out west to build it, or used a lot of oil to transport the lumber.”

Mr. Gundersen had a rough feeling for all of this 16 years ago, when he started building a simple A-frame house here for his first wife and their son, Ian, now 15. He wanted to encourage local farmers to use materials like wood and straw from their own farms to build low-cost, energy-efficient structures. So he used small aspens that were crowding out young oaks nearby.

“I would just carry them home and peel them,” said Mr. Gundersen, who later realized he could peel them while they were standing, making them “a lot lighter to haul and not so dangerous to fell.”