The Owner Built Home - Chapter 7: Wood Framing and Structure

This chapter excerpted from "The Owner-Build Home" examines secure, proven wood framing methods.


| January/February 1972



wood framing - rational framing systems

Ken's hand-drawn illustrations are found throughout the book. This depicts four possible approaches to wood framing.


ILLUSTRATION: KEN KERN

Ken Kern, author of The Owner-Built Home and Homestead, is an amazing fellow and everyone interested in decentralist, back-to-the-land, rational living should know of his work. Back in 1948 he began collecting information on low-cost, simple, and natural construction materials and techniques. He combed the world for ideas, tried them, and started writing about his experiments. We're excerpting chapters from Owner-Built Home and Owner-Built Homestead. Here he considers wood framing and structure. — MOTHER EARTH NEWS

Why on earth do home builders continue to ignore the more rational approaches to structure? They ignore the "skeleton of the house" and go all-out for affectation and trimmings. Take frame houses, for instance. Conventional stud-walls are inefficient; while overdesigned they retain weak joints; both erection labor and materials are wasted; they offer maximum fire hazard; erection is slow and thus vulnerable to bad weather.

Extensive studies into the structural engineering of houses have been made by various private and government agencies. One government report, Strength of Houses, maintains:

Houses have never been designed like engineering structures. Since prehistoric times, safe house construction has been found by the tedious and wasteful method of trial and error. If the modern research that has proven so successful in the solution of other problems had been applied to houses, not only would homes be more satisfactory as dwellings but, much more important, the cost would be much less. This would be an outstanding contribution to the problem of providing acceptable houses for the low-income groups in this country.

Note the lack of engineering approach in house-building practice today. It is customary to assume that walls, floor, and roof contribute nothing to the strength of the building! All loads are supposed to be carried independently by the frame. And all stresses and loads are analyzed separately for each structural component! Design loads are calculated for compression, traverse, impact, and racking on walls, floor, and roof. Dead loads (gravity weight of construction) are added to live loads (objects or persons on the floor). To these the builder must add calculated wind, water, and snow loads. Then, to complicate matters more, the builder must be acquainted with the strength of various materials and fastening methods; the modules of elasticity, stress, shear, and deflection for each independent member, as well as for the effective cross-sectional area, grade, and species of each variety of material used!

In the engineering approach the usual building practice of analyzing each structural component separately is replaced by a consideration of integrated structural effect; and a deliberate attempt is made to have the foundation and roof function as extensions of the wall — to eliminate the separation of function between wall and roof, floor and foundation.

A structural system has only four basic forces to overcome; compression, tension, bending, and shear. Bending occurs when a weight or force is placed at a distance from a support. Shear, in mechanics, means a thrust outward at right angles to the stress. With these basic structural reactions in mind, various framing systems can be evaluated and compared in relation to strength per unit of material and of time expended in fabrication. Wood was inefficiently used, of course, by early settlers in building cabins of massive logs cut from trees. Later, with the advent of power-driven sawmills, wood-frames having lighter members were developed and less wood was required. The post-and-girder structural system provided a transition between the log cabin and the currently employed vertical-stud-wall system of construction, which in some ways, however, marks a decline from the post-and-girder design.





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