San Diego GreenLife

by Laura Silver

Photo credit Barry Rustin

I’m mildly obsessed with trees — real trees, images of trees, and almost anything with a leaf motif. So it’s no wonder I keep going back to my November/December 2007 Natural Home magazine, with its article on Chrysalis Farm — a sustainable home designed by whole-tree architect, Roald Gunderson.

Gunderson’s designs use whole young trees in place of milled lumber, in a variation on post and beam architecture. The trees average 6 to 12 inches in diameter, and are chosen from diseased, invasive, or wind-bent specimens.

Rather like thinning plants in a garden, this type of young-growth forestry leaves woodlands healthier and allows the oldest, tallest, and straightest trees — the nearly irreplaceable trees favored by the logging industry — to continue to live, thrive, and reproduce.

Appropriate younger trees are up to 100 times more abundant than straight, older trees, and will replace themselves in less than 20 years. In the meantime, the older trees will continue to grow, and sequester increasing amounts of CO2.

Young, unmilled trees used in construction actually sequester a ton and a half of CO2 for every ton of wood used, and are locally available in most areas. So instead of producing carbon through the milling and transportation processes, they help to reduce it.

Photo credit Barry Rustin

There are also excellent engineering reasons for choosing whole trees over milled lumber — even over steel or concrete framing. Wood in its living-tree form has intact and continuous wood fibers that give it a load-bearing strength 50% greater than milled wood. It has the same compression strength as steel, and twice the tensile strength.

Because tree species that would be deemed unsuitable for milling are perfectly usable when left intact, nearly any type of young tree is an option.

This type of “tree house” may be safer, too. In fire conditions, round timbers char but are harder to burn than milled lumber; they do not get brittle or weaken like steel and concrete. The axial and rotational stability of the trees might give a home an edge in earthquakes and hurricanes, (in theory, no study data are available).

Owners of Gunderson’s designs say the feeling is like living in a grove of trees. Photos show organic curves where most homes have stark angles. When the bark is left on, the trees appear to grow through the building.

Gunderson uses straw-bale insulation in walls and roofs, fire-resistant roofing and exterior wall treatments, and passive solar design that helps keep homes warm in the cold Wisconsin-area climate. With modifications, similar designs could keep out the heat of Southwestern summers and create a far more fire-resistant home than standard construction techniques.

While it seems as though the custom nature of building with unique tree shapes would be expensive, Gunderson’s structures are touted as coming in below the national average for per-square-foot cost, as well as keeping more of the construction money in the local economy.

Photo credit Barry Rustin

I have to admit to being a little skeptical about the overall costs. After all, I built my own supposedly-cheaper-than-normal sustainable home — and learned a thing or twelve in the process. I suspect Gunderson’s owners paid in time and effort what they did not spend in dollars — and I wonder if the architect’s fees were included in the listed costs.

But still, I like the concept of Whole Tree Architecture. Even at equal or higher costs than average, I’d continue to be drawn to the idea. I imagine I’ll keep looking at it, just as I keep looking at trees.

Resources:

Roald Gunderson’s Web Site with photo gallery

Article in Natural Home magazine: Nov/Dec 2007: Deep Roots, Strong Branches