Thermally modified woods have many of the same attributes as western redcedar – dark colour, dimensional stability, decay resistance, and relatively low strength – and are poised to compete for many of the same markets. Although thermal modification generally increases durability, both species and modification process can affect the degree of decay resistance. There are currently insufficient data on the durability of thermally modified white spruce. The present work evaluates the durability of white spruce modified at two temperatures using the decay fungi Postia placenta and Gloeophyllum trabeum. Western redcedar was included in the study as a reference species of naturally durable wood. A laboratory decay test classified the wood modified at 190°C as moderately resistant to both fungi, while the wood modified at 212°C was resistant to both fungi. In comparison, western redcedar heartwood was classified as resistant/highly resistant to P. placenta, and highly resistant to G. trabeum. In addition, three medium- or long-term decay tests were initiated. The Accelerated Field Simulator (AFS) test will generate decay resistance data from an accelerated above-ground exposure. The L-joint test will generate decay resistance data specific to the window industry. The field stake test will generate decay resistance data from exposure in ground contact. Together these tests aim to provide comprehensive information on the performance of thermally modified spruce in a range of environments that will help producers gain access to new markets.