Whether the log cabin or home is being built with cedar, larch, pine or oak logs, the structural strength of the proposed log specie may be in question. Of course, certain portions of a tree can be used as structural members in building a cabin. Good rules of thumb have been used in the past by experienced log home builders.
At present, a new building code is being used to provide answers to the question of structural strength. That new code is the International Building Code, 2006. (IBC). This code may or may not apply to certain counties or states as the IBC must be adopted by the local building authority.
The IBC requires inspection by a certain grading agency or a structural engineer of record to estimate the structural strength of the log and the suitability of logs for structural application. This is covered in the IBC, section 2303.1.10.
The grading agency establishes the criteria to guide the strength reducing log characteristics such as holes, splits, checks, and knots allowed for the proposed log specie. The grading agency determines the stress grades and, in turn, derives the strength values.
Of course, the grading strength values are important. Other issues are to be considered; such as connections of round or non-standard shapes because they are custom made and are used without experimental testing information.
The International Building Code (IBC) is not available to all log home builders, as the locale that the builder builds in may not have adopted the IBC.
The best approach to using logs in constructing a log cabin or home is to use the expertise of any experienced log home builder. An alternative would be to obtain the expertise of a licensed Structural Engineer.