How to Drill Engineered Wood and Laminated Beams


Unlike solid timbers, engineered joists and laminated beams consist of thin wood layers bound by adhesive. Using a process similar to plywood manufacture, laminated beam manufacturers create thick, timber-shaped beams from thin solid wood strips. The most common type of engineered joist, the I-joist, consists of a thin, vertically oriented chip board sheet sandwiched between a set of small laminated beams. Although drilling through engineered wood products is similar to drilling through solid timbers, builders must follow manufacturers' guidelines regarding hole placement. Placing holes too close to the edges or ends of the engineered joist or laminated beam compromises the unit's ability to safely bear structural loads.

Things You'll Need

  • Power drill
  • Wood drill bit
  • Tape measure
  • Pencil
  • Square
  • Determine hole size according to your beam or joist manufacturer's guidelines; manufacturers specify hole size in maximum inches or as a proportion of the beam's total thickness.

  • Attach the wood drill bit to the power drill. Review the manufacturer's hole placement restrictions; holes that are too close to the ends or edges of the beam compromise the beam's strength. Manufacturers calculate hole placement based on specific values, such as beam thickness, length and width.

  • Stretch the tape measure across the beam's length and use a pencil to mark the horizontal position of the hole relative to the beam's length. Position the tape measure approximately 1 inch to the side of the horizontal mark, latch the tape's tang onto the beam's edge and stretch the tape measure across the beam's face. Mark the vertical position of the hole with a pencil.

  • Position the tape approximately 1 inch on the opposite side of the horizontal mark, stretch the tape across the beam's face and use a pencil to make an identical vertical position mark on the opposite side of the horizontal mark. There are three marks on the beam's face; the center mark represents the horizontal position of the hole and the surrounding, parallel marks indicate the vertical position of the hole.

  • Lay one side of the square flat against the beam's face. Butt the other side of the square flush against the beam's bottom. Align the side of the square on the beam's face with the horizontal hole mark. Draw a pencil along the square's edge to create a layout line that begins at the beam's corner and extends vertically through the horizontal hole mark; this line runs perpendicular to the beam's edge.

  • Lay the square over the vertical hole marks; the square must pass through both marks. Draw a pencil along the square's edge to create a straight line that runs between the parallel vertical hole marks. Remove the square from the beam. Two lines run across the beam's face; a horizontal line and a vertical line. The intersection of the lines represents the precise vertical and horizontal position of the hole.

  • Press the drill bit's tip or pilot against the beam's surface at the intersection of the lines. Drill straight through the beam until the bit protrudes from the beam's opposite face.

Tips & Warnings

  • Avoid drilling through engineered I-joists by using the prescored knockouts in the joist's web; whack the knockout hole with a hammer to pop a portion of the web from the joist. After removing the knockout, simply run wires, conduit or pipe through the hole.
  • Do not drill through engineered wood beams without consulting your manufacturer's guidelines, an architect or engineer. Improperly drilled beams can fail and lead to structural damage or personal injury.

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