Wood Structure, Properties, and Manufacturing

Wood Structure and Growth

• Cells are microscopic, hollow tubes in trees
• Cells transport water vertically
• Ray cells transport food horizontally
• Lignin holds cells together
• Cambium layer is the outermost growth ring
• Growth rings form inside the tree
• Growth rings indicate tree age and maturity
• Pith is the center of the tree

Wood Properties

• Wood is hygroscopic, absorbing or releasing moisture based on its environment
• Wood is graded by the National Lumber Grades Authority (NLGA)
• Visual and machine stress testing (stiffness and strength) evaluates wood
• Wood is a naturally grown material, distinct from steel and concrete
• Wood has grain orientation and load duration characteristics
• Wood can be treated to prevent decay and fire
• Moisture content impacts wood
• Load sharing capabilities are relevant factors
• Member size is another key factor

Wood Manufacturing

• Logs are cut from trees
• Logs are transported to the mill
• Bark is removed from the logs (debarring)
• Logs are cut into timber
• Surfaces of lumber are smoothed
• Green lumber is dried
• Lumber is graded

Wood Seasoning

• Air seasoning is one method
• Kiln seasoning is another method

Wood Types

• Softwoods
• Hardwoods

Wood Species Groups

• Spruce-Pine-Fir (Spr)
• Douglas Fir-Larch (D-Fir-L)
• Hemlock Fir (Hem-Fir)

Building with Wood

• Sheating for roof rigidity

• Joists for structural support

• Beams for intermediate support

• Build-up timber beams

• Columns are vertical support

• Stud wall (multiple vertical supports)

• Wall plates (bottom wall spacers)

• Lintels for windows, placed horizontally

• Sill plates, positioned flat on the foundation