Historic covered bridges and current timber bridges can be vulnerable to damage from biodeterioration or fire. This guide describes procedures for selecting and applying inplace treatments to prevent or arrest these forms of degradation. Vulnerable areas for biodeterioration in covered bridges include members contacting abutments, members near the ends of bridges subject to wetting from splashing and members below windows or other openings that allow entry of wind-blown precipitation. Pressure-treated timber bridge members can be vulnerable when untreated wood is exposed by field fabrication...