When Dimensional Lumber Can't Do The Job

What to do when dimensional lumber just won't work.

The majority of building projects consist of dimensional lumber (2x4, 2x6, 2x8, 4x4, etc.) which is produced by sawing the boards from trees of various species. They are available in typical thicknesses of 3/4", 1 1/2", 3 1/2", 5 1/2" and 7 1/4" and typical widths of 3 1/2", 5 1/2", 7 1/4", 9 1/4" and 11 1/4" and lengths typical up to 20'-0" to 24'-0". The main advantage of dimensional lumber is price. There is less overhead required to produce building material in the wood mill than there is to produce engineered lumber in a factory. The disadvantages of dimensional lumber are numerous including bowed and twisted boards, knots, non-uniform width and thickness, weak points due to the natural grain of the wood and, one of the biggest, availablity of lengths over 20'-0".

There are many types of engineered lumber.

LVL or Laminated Veneer Lumber which is solid sawn strips of thin veneers of wood which are glued and pressed together to form beams typically 1 3/4" wide by depths ranging from 9 1/2" to 24" and lengths of up to 48'-0". This system of overlapping and pressing together these strips of wood eliminates the issues of bowing, twisting, knots, grain and short lengths. Typically used in multi-ply members the strength is many times greater than dimensional lumber of similar size.

LSL or Laminated Strand Lumber which is wood that has been chipped into small thin pieces of various sizes and shapes which are then run through specialized machinery which alligns the pieces length wise, applies the bonding agent and then presses the material into a solid beam that can range in depth and length similar to that of LVL but is available in a greater number widths without having to laminate multiple pieces together in the field. LSL is typically rated lower than LVL structurally but is still many times stronger than its dimensional counterparts.

Glulam Beams are a popular engineered lumber due to their availability in architectural grade which is manufactured to be left exposed and finished for a rustic or natural look. They are produced by utilizing culled lumber that has too much twisting or bowing to be useful as dimensional lumber and gluing and pressing them together. When they are finished pressing the odd sized boards together and the glue is cured the beams are then planed down to their finished sizes similar to the process by which dimensional lumber is finished. By pressing the imperfect boards together and gluing them in place each layer adds to the strength of the whole beam and all the individual plies work to oppose the individual imperfections which in turn creates a beam with a greater strength than that of its parts. These beams are available in typical as well as custom widths, depths, lengths and even shapes. Glulam beam manufacturers can produce arched beams that can used in building methods similar to steel framed buildings.

I-Joists are maufactured joists with a top and bottom chord (referred to as a flange) similar to a truss but with an OSB (Oriented Strand Board which is the sheet good equivelent of LSL) web that runs continuously the entire length of the joist. They are manufactured with both dimensional lumber flanges and engineered lumber flanges and range in width and depth according to the required load carrying capability. I-Joists are available in lengths up to 60'-0" and have the advantage of unifornity between pieces. They are stronger than dimensional lumber and the availability of such greater lengths makes the I-Joist a great solution to long floor joist and roof rafter spans.

As I said at the beginning, you are going to use dimensional lumber for the majority of your framing and building projects but the availability of engineered lumber can simplify your project when you are faced with those situations where you just can't make a 2x6 stretch quite far enough or a 2x12 carry just a little more weight. Your local truss manufacturer will be educated on engineered lumber and will be able to help you utilize it in the most efficient way possible so stop by and see them the next time you get into one of those head scratching situations.

Coleman Klineline - Senior Component Designer - Capital Structures

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