The lifespan of natural Douglas fir versus pressure-treated pine can vary depending on several factors, such as the environment, climate, and how well the wood is maintained. In general, pressure-treated pine tends to have a longer lifespan than natural Douglas fir.
Pressure-treated pine is treated with chemicals to resist rot, decay, and insect damage, which can extend its lifespan to 20 years or more.
On the other hand, natural Douglas fir has a shorter lifespan and may last around 10 to 15 years, depending on the conditions it is exposed to. It is also more susceptible to rot, decay, and insect damage than pressure-treated pine.
It's important to note that both types of wood can be affected by various factors such as moisture, exposure to sunlight, and temperature changes, which can impact their lifespan. Regular maintenance such as staining, painting, or sealing can help prolong the life of both types of wood.