Knowledge Base

Wood

 

A number of factors come into consideration when selecting materials for truss construction. Primary considerations are (1) appearance, (2) strength and (3) resistance to the surrounding environment. The proper mix of characteristics can be achieved by selecting an appropriate species of wood, indicating the required surface finish and designating any required material grade. Chemical treatment of timbers may also influence performance properties.

Southern Yellow Pine, Douglas Fir, Cypress, Glulams and Reclaimed Timbers are good choices for Structural trusses. The strength characteristics of these materials fall in a similar range, and generally work as equal alternatives for similar spans, roof loads and member sizes. Glulams of equal size are generally superior from a structural standpoint. For Reclaimed Timbers, one must consider the species and condition of the material when evaluating for structural integrity.

Western Red Cedar and Cypress are known for their natural resistance to insect or moisture-related decay over time.  Whereas Cypress has good strength characteristics, Western Red Cedar lacks the strength of the other materials above.  If member sizes are large enough, there are circumstances where Western Red Cedar is acceptable from a structural standpoint.  What Western Red Cedar lacks in strength, it makes up for in appearance.  Western Red Cedar is frequently the material of choice for pure Decorative trusses, but should be checked thoroughly if intended for use in Structural applications.

Cypress is one of the most versatile timbers available for use in exterior applications.  It is visually attractive (light in color with small knots), has good strength properties, and is resistant to both insects and moist environments.  The shortcomings of Cypress are its slight price premium and more limited availability or longer lead times.

Surface Textures - The two most common surface textures used are Rough Sawn and S4S.  The Rough Sawn material SWC supplies is often referred to as “Resawn” or “Band Sawn”.  This is because the timbers are cut on a large band saw and have a uniform “fuzzy” finish.  Our Rough Sawn material does not have the prominent, circular mill marks associated with large circular saws of older saw mills.  S4S material, or “smooth on four sides” is the planed or smooth finish most individuals are familiar with as used for dimensioned lumber. It is common for many customers to select Rough Sawn finishes for exterior installations and S4S finishes for interior work, but surface finish is purely a matter of preference. 

One thing to be aware of from a dimensional standpoint is that standard Rough Sawn material is supplied to full dimension, i.e. a Rough Sawn Four-by-Six measures 4” thick by 6” wide.  Standard S4S dimensioned beams have narrower dimensions because of planning operations.  Net dimensions vary somewhat by size and source mill, but our material usually run 1/2” smaller than Rough Sawn material.  Hence an S4S Four-by-Six normally measures 3-1/2” thick by 5-1/2” wide.  This being said, we can special order material custom-milled to any dimension with any surface texture.

Faux Surface Texture - If a customer finds the surface irregularities, size constraints or price premium of true antique material undesirable, SWC offers several faux finishes that can be applied to new timber to achieve a Hand Hewn or Time Worn appearance associated with age. Price of this material falls between new, unaltered wood and reclaimed material.  A critical step following the faux surface finishing is the stain or antiquing process applied by the customer or his painter.

Material Grades - There are several things to know about grading systems. First, while grading levels appear to be similar for various woods (#1, #2, Select Structural, etc.), different species are typically graded according to standards established by an organization presiding over that species (Example: Western Wood Products Association, Southern Pine Council, etc). Grading is used to evaluate the physical characteristics of a piece of wood and rate it with regard to strength and appearance. Various standards organizations approach the grading process differently. Second, even though a grade may exist in one of the standards organizations’ reference books, it may not be commercially available or economic to purchase in different regions of the country. As a result, SWC fabricates most of our trusses with readily available materials and grades stocked in the region. For some species, multiple grades are available and for others some grades are generally unavailable unless ordered special from mills providing that material. Click here to return to Products - Timber Trusses