When most people hear the word “durability” in relation to wood, they immediately think of its ability to withstand dents and scrapes. However, in this context it specifically refers to a wood’s ability to resist elemental and natural forces of decay. (The former notion of durability equating to physical toughness would be better explored through Janka hardness and Modulus of Rupture values.)

Degradation can occur from fungus (caused by cycles of rain/moisture), or from termites or other boring/destructive insects. An overall chart defining the terms used to describe a wood’s durability in direct ground contact:

Classification Service Life(in years)
Very Durable 25+
Durable 15-25
Moderately Durable 10-15
Non-Durable 5-10
Perishable less than 5

 

This durability assessment is only based on the tree’s heartwood, and not its sapwood—as only the heartwood, due to its extractives, has any appreciable degree of durability; in nearly all instances, sapwood should be considered perishable.

Some genera of Bamboo are only expected to last 6 months to 3 years in direct ground contact. On the other end of the spectrum is wood such as Teak, which is well-known for its durability, and is frequently used in boatbuilding and other outdoor applications.

In addition to the length of time the wood can physically maintain its structural integrity, there’s also the matter of a wood’s weathering characteristics. Weathering can’t be as clearly expressed in a single number or measurement, but overall, woods with good weathering characteristics exhibit limited photo-degradation (caused by UV rays in sunlight), as well as above-average resistance to contraction and expansion, warping, and surface checking due to seasonal changes in temperature and humidity.

Because of this vague definition, only woods that have notably good (or notably poor) weathering characteristics will be noted. (Again, Teak is noted for both its excellent durability and its superb weathering characteristics.)

  • Caleb

    I am interested in the durability of Eastern Hemlock. I see that it is rated as “non-durable” with a service life of 5-10 years when in “direct ground contact”. Do you have any idea what the durability might be when used outdoors but not in direct contact with the ground and covered (I would like to use some large old growth Eastern Hemlock beams for porch columns). Do you have any resources that you could point me to that might help me in this?
    One last question, Is there a durability difference between old growth Eastern Hemlock (harvested in 1790) versus new Eastern Hemlock.

    Thank so much for your time,

    Caleb Tittley
    254-716-1013

  • Joe Bloggs

    A friend is interested in buying an Eric-32 boat (still unfinished) that two brothers spent thirty years building. One bro died and the other bro is now too elderly to continue. Allegedly the wood is Mahogany (no idea what type) Allegedly the best boats were built from an Indian Teak known as Ironwood which is allegedly so hard that the marine worms won’t eat it. How is Mahogany going to compare? The boat has never been put into the water but rainwater that has accumulated inside the hull constantly drips out of joints between the planks. Personally I wouldn’t touch the boat with a barge-pole as to me it just looks like several tons of firewood.

    A GRP version of the boat was produced later on and was known as a Westsail 32. Unfortunately these are not noted for their speed. In fact the cognoscenti of blue water yachtsmen have nicknamed the model “Wet Snail”.

    I fear that my friend will just be putting his money down the toilet if he buys the boat, but how durable is Mahogany?