In the usage of timber for structural purposes, the strength properties of the timber are of prime importance. The strength required of a timber varies, depending on the load that the structure is expected to carry. Obviously, the heavier the loading, the stronger the timber required. The strength properties of most of the common timbers have been studied and based on conventional standards, the timbers have been grouped into Strength Groups, as shown below: -

Strength Group A: Extremely Strong
Strength Group B: Very Strong
Strength Group C: Strong
Strength Group D: Weak

Strength Groups of Timbers and Their Applications

* The strength groups mentioned here are based on Engku Abdul Rahman’s (1988a,b) classification wherever possible. For timbers that have not been classified by Engku Abdul Rahman, their strength grouping is based on Burgess (1958). 
** Malaysian Standard Code of Practice for Structural Use of Timber (MS 544:Part 2:2001). 

Strength Groupings of Timbers

* Commercially available
Source: Malaysian Standard Code of Practice for Structural Use of Timber (MS 544:Part 2:2001).