Life Expectancy Of Wood


What is the life expectancy of wood that was used in an attic truss? Does fire retardant change the life expectancy?


There are many factors that affect the strength, which in turn affects the life expectancy, of wood. The strength of wood depends heavily on the direction of the loads with respect to the grain. The moisture content (MC) of the wood also will have an impact on the strength. All other things being equal, the drier the wood, the stronger it will be. Changes in strength properties occur between 0-30% MC. The MC is dependent on relative humidity and temperature. If your attic is well ventilated, this should not be a factor. Strength properties of wood generally have an inverse relationship to temperature; that is, strength decreases when temperature increases and strength increases when temperature decreases. At temperatures greater than 200 degrees Fahrenheit, strength loss is irreversible. Normally, this also will not be a factor in an attic.

Even though chemical solutions reduce wood's strength, chemicals are used as preservative and fire-retardant treatments (FRT). The reduced capacity of using FRT lumber is taken into account when originally designing the attic truss. Therefore, whether or not your attic truss was built using FRT lumber, your attic trusses should not decrease in life expectancy.

All things considered, if your attic is well ventilated and your trusses were designed properly taking all factors into consideration, your attic trusses should last indefinitely. There are wood structures still standing that were built centuries ago. For example, the Gol Church at the Norwegian Folk Museum in Oslo is over 800 years old.

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