When you decide to build something, these days you have a choice of four primary building materials :

  • Steel
  • Concrete
  • Processed Wood
  • Wooden timbers

Which one would you guess is the most sustainable?

 Unmilled timbers are what we using to build our house, which is currently a tiny subset of the timber frame industry.  Unmilled timbers structures (and especially branching timbers) solve a number of building and environmental issues, but many builders shy away from a material they are uncertain about.  That may soon change.

In late October I witnessed a test of their strength at the U.S. Forest Products Lab in Madison, WI.    Whole Trees Architecture and Construction, in partnership with the USDA Forest Products Lab,  is currently conducting the first-ever, destructive testing of branching round timber members.

Check out a video about it here.

Whole Trees Architecture and Construction, the company that we are working with, selects trees for construction by using the Worst Trees First Method.  They walk into the woods and seek out what some people call trash trees.


A part of our woods where the trees are seriously crowding each other.

Because these trees are plenty strong to build with.  They make excellent unmilled timbers and create a healthier forest by thinning.  Working with small trees is efficient because there is an abundance of these smaller trees out there.  New forests have as many as 1,000 stems per acre — a mature forest is more like 60 stems per acre.

However that extra 940 trees – all that wonderful, green building material — is not being used by conventional builders because they are unfamiliar with it.  That’s why this testing process at the Forest Products Lab is so important.

With structural guidelines in place to support use of round timbers in construction, forest owners throughout the United States could supply the construction industry with a low energy, highly abundant, carbon sequestering, wasted forest resource, decreasing energy use in the construction industry and promoting energy independence.

In the last 10 years, the USDA has advanced its understanding of round timber and the enormous potential for the construction industry represented by this resource . USDA secretary, Tom Vilsack recently urged the Forest Service to “develop new markets” for forest by-products which encourage healthy timber management. Small-diameter, round timber is an abundant by-product of healthy timber management and could serve emerging green commercial markets if technical barriers, specifically round timber “connections”, can be solved.

Bruce Allison, Registered Consulting Arborist and Adjunct Professor Forest and Wildlife Ecology, UW-Madison, calls this testing the groundwork for a new chapter in sustainable forestry.

He says, “By acquiring data on the load carrying capacity of small diameter trees, they are clearing the way for safe, reliable use of unmilled tree stems in residential and commercial construction. Their creative work will add value to by-products of forest thinning and promote recycling of what otherwise would be wood waste in the urban forest. And the best part is the organic beauty resulting when the natural shape of the whole tree is brought indoors as an integral part of our dwellings.”

This particular test is being performed using ash trees because we are about to have a lot of dead ash trees in our part of the world.  The Emerald Ash Borer is winging its way into Wisconsin.  Madison alone will have more than 2,000 dead ash trees soon, and these urban trees will have to be removed.  Instead of being sawed into little pieces, they could be used as building material, if the strength of their branching members can be quantified.

Whole Trees has built with branching tree timbers for years because branching columns reduce the span length needed to hold up the beams, and they provide lateral stability usually created with artificial bracing.

Intuitively it seems that the natural fiber pattern of a tree’s branching point would be as strong, if not stronger than any man-made mechanical connection.  (And it certainly seems a lot more beautiful to this writer.)

 No one has tested the strength of branching timbers –


The first forked ash timber sacrificed to science.

Now the Forest Products Laboratory and Whole Trees have been awarded a USDA grant to perform “destructive lateral and axial testing and analysis” on almost 100 trees in the hopes of furthering the structural understanding and scientific parameters regarding branching trees to impact building codes and encourage use of this renewable, local, durable, cost-effective building material.

The first tree was placed in what is fundamentally a giant vice and pressure was applied.  At 4,500 pounds of pressure, the timber gave a resounding crack and broke.  One down – about 90 more to go.

After all of the trees and the data has been crunched, I’ll report the findings.

(On our own land, the trees selected last summer will start being felled and prepared in December!)

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