Evaluating naturally durable wood species for repair and rehabilitation of above-ground components of covered bridges

More than 1,500 covered bridges remain in the United States. They are a unique part of our history; thus, replacement of bridge components is an equally important part of preserving this uncommon style of craftsmanship. The goal of this project was to evaluate seven wood species for their durability in above-ground field exposure. Chemical analysis was also conducted using gas chromatography-mass spectrometry (GC-MS) for fatty acids and terpenoids in an attempt to correlate extractive content with durability. Extracts removed from the durable wood species were also tested in laboratory bioassays to determine their biological activity against wood decay fungi and termites. This report serves as a guide for the use of these naturally durable wood species for rehabilitation of above-ground components of covered bridges and incorporates the results of filed and laboratory tests into the final recommendations.