Constructing Wood Beams
Wood beams are used extensively in wood frame construction and can be either fabricated by a wholesale manufacturer or constructed at the jobsite. Wood beams or girders can be solid or assembled from smaller wooden components. Laminated beams consist of small strips that are glued together with waterproof adhesive to meet the required dimensions. A stack of strips equal in height to the depth of the beam are glued together in horizontal layers and all sides are finished to a clean, smooth surface.
The strips are joined with interlocking “fingered” joints to resist tensile, compressive and bending stresses. Built up beams can be constructed in a variety of configurations. A hollow box beam uses single solid members for the top and bottom “flange.” A plywood “web” is nailed or glued onto the edges of each flange either in full strips or in equally spaced segments.
Another type of built up beam is made from framing lumber nailed or bolted long dimension to long dimension (side to side). It generally consists of two to four vertical layers (members) which are either nailed adjacent to each other or with plywood spacers inserted between each pair of boards. The framing members used to make this type of beam range in size from 2 x 6 to 2 x 12, but sometimes can include a board one-inch wide in nominal thickness to bring the overall beam thickness flush with the wall thickness.
For longer beams made of two or more layers of boards nailed end to end, it is a good engineering practice to stagger the joints in alternating layers. Built up beams are not as strong as laminated, steel or flitch beams (a steel plate sandwiched between two boards). But built up beams can be extended to span almost any distance and are the least expensive in terms of materials. The simplest type of built up beam can be constructed by following three easy steps.
Step 1 - Cut the Individual Boards
Select straight boards that are neither twisted, crowned, or bowed for the beam components. Measure the length of the beam on one of the boards. Use a triangular measuring square to make a straight, square cut. For accuracy, cut directly alongside the pencil line with a circular saw, keeping the thickness of the saw blade on the scrap side of the board. Use the original as a template to trace and cut the other board (or boards).
Step 2 - Cut the Plywood Spacers
Cut plywood into squares or strips to be spaced evenly between the boards. Cut the strips a few inches in width by one inch less than the width of the beam, so that the top and bottom edge of the plywood is set back from the edge of the beam.
Step 3 - Assemble the Beam
Place the strips flat on the face of one board, spaced a few inches apart. Place the second board on the plywood so that the two boards are flush all around. Using #16 nails, nail the two boards together from both sides in a grid pattern. Be sure to nail through the plywood strips. If 2 x 6 studs are to be used for the wall construction, another layer of plywood and an additional board are used to bring the total thickness of the beam to 5 ½ inches.