Choosing the Best Timbers for Your Job

When choosing timbers there are many factors that are important to consider, including which drying method is used, if the piece is structurally strong enough for it's purpose, and how it is cut, for both structural purposes and beauty.

Some common timber abbreviations and terms:

  • FOHC=Free of Heart Center
  • BH=Boxed Heart Center
  • S4S=Surfaced four Sides
  • SFA=Selected for Appearance
  • Wane=Bark, or lack of wood from any cause, on the edge or corner of a piece of wood.
  • Shake=A lentghwise separation of the wood between or through the growth rings.
  • Dense Grain=Has six or more annual rings.

                   Free of Heart Center                                                      Boxed Heart Center

               Green                           Dry                                               Green                           Dry

                       

Drying Process

There are a few timber drying options to choose from. There are benefits and drawbacks to each. When considering which method you want to use, consider what the timber will be used for as well as how much you want to spend.

Green or Unseasoned Timbers

The moisture content of our green timbers is 30-35%. Green timbers are the least expensive and quickest shipment. These timbers will shrink, in width and thickness as the timber begins to dry. Timbers cut FOHC, (free of heart center) help compensate for excessive cracking that will occur as the timbers naturally dry. Our timbers are sprayed with an anti-stain solution which helps limit mold that may occur in a natural drying process.

Kiln Dried Timbers

The moisture content of our KD timbers is 15-19%. Kiln drying eliminates potential mold problems associated with green or unseasoned timbers. Drying typically takes 10-15 days, and removes loose water in the wood fibers that would normally take months or years to dry. Drying this way also minimizes the size and extent of cracks that will occur if dried too much. The cost of drying timbers is only 15-20% more than green or unseasoned timbers.

Standing Dead Timbers

Standing dead timbers can be a cheaper alternative to KD timbers, but are generally smaller in diameter and shorter in length. They may be infested with insects creating bug holes. A sap stain also generally occurs with standing dead timber, although it does little structural damage to the timber. Kiln dried timbers can offer a better alternative to the quality and limited size of standing dead timber.

RF (Radio Frequency) Drying Timbers

RF drying timbers is a faster, more costly process that dries timbers from the core out. To insure the proper quality, timber must be cut larger than normal. Because the wood is dried from the center out, care must be taken not to over dry the timber causing interior cell structure to collape, and degrade the strength of the timber. After RF drying, timbers should be re-sawn to square the timbers. This compensates for excessive shrinkage, twist and warp.

Custom Fabrication

We can custom cut wood for a wide variety of projects. Here are a few examples of custom fabrication that we have done:

Bridge with fabricated & pressure treated beams                       Custom cut corbels

                    

                        Custom peeled log                                     Lathed, turned and sanded log

                             

There are a multitude of other custom cuts and designs we can do. If you already have an idea of how you would like your design to look, just draw it for us. Feel free to contact us with your ideas and questions.

Structural Strength of Timbers (Design Values)

The structural strength of the fibers in timbers must be strong enough to hold the weight required for each job. The structural strength of timber is described as “design values.” This is a grouping of timbers with similar physical properties together to meet the requirements of the specific end uses. Design values for timbers indicate the basic working stresses and stiffness’s to be used for structural design purposes.

Timber structural strength properties are assigned to five basic properties: fiber stress in bending (Fb), tension parallel-to-grain (Ft), horizontal shear (Fv), compression parallel-to-grain (Fc), and compression perpendicular-to-grain (Fc |). The modulus of elasticity (E) measures the amount a piece of lumber will deform in proportion to an applied load under elastic range stresses. It is a measure of stiffness and not a strength property.

Extreme fiber stress in bending values are calculated for pieces loaded on the narrow face for Beams & Stringers, and on either the narrow face or wide face for Dimension Lumber. Flat-use adjustments are provided for Beams & Stringers and Dimension Lumber, and depth-effect adjustments are provided for Structural Decking.

To see the design values chart for all the common timber species click here.