AbstractThe application of linear elastic fracture mechanics is ideally suited to estimating the strength of notched timber elements because wood is quite brittle with respect to tension across the grain. Elements with notches more than a few millimetres deep behave in a brittle manner. Some of the early research in developing this practical application of linear elastic fracture mechanics is presented.In mathematical terms the stress field in the vicinity of a notch contains at least one and sometimes two stress singularities. The magnitudes of these singularities are defined by stress intensity factors. Crack initiation, associated with a predictable size effect, occurs when these factors reach critical values.This paper gives equations for the stress fields around an orthotropic notch root. It also provides a simple method for computing stress intensity factors and size effects in notched structural elements. Some examples of stress intensity factors for timber elements containing zero and non‐zero angle notches are listed. Critical stress intensity factors for timber, related to density, are given for a series of notch types. Measured effects on strength arising from interactions between loading configurations are also presented. Copyright © 2006 John Wiley & Sons, Ltd.