Fence Post Spacing Under Wind Load: The Widest Bay a Timber Post Can Carry Before Bending Governs

A solid garden fence is a sail, and its posts are the masts. This study computes post bending stress under a stated gust pressure of 0.55 kN per square metre on a 1.8 m solid fence, with each interior post carrying one bay and acting as a 125 mm square timber section of stated allowable bending stress 8 MPa. Stress rises in direct proportion to bay width: 4.92 MPa at the conventional 1.8 m spacing, reaching the allowable limit at a spacing of 2.92 m and 8.2 MPa at 3.0 m. Widening bays from 1.8 m to 3.0 m would save about 6.7 posts over a 30 m run, but it spends the entire structural margin to do so. The practical rule is to keep bays at or below about 2.4 m on exposed sites, where a margin of roughly a fifth remains, and to treat the common 3 m panel span as suitable only for sheltered gardens or stronger posts. SIMULATED, NOT MEASURED.