Rigid foam-board insulation provides a barrier between the outside elements and the inside of your home. Cutting the foam board with the correct tool keeps the edges of the board straight. Jagged cutting edges create air spaces between pieces of foam after installation. Air gaps present in between pieces of insulation cause a loss in R-value. An R-value loss reduces the efficiency of the insulation to keep your home energy efficient.
Place a piece of insulation board on a stable work surface.
Pull a tape measure along the piece of insulation board. Mark the cut location on the board with a pencil. Place a second cut mark on the surface of the insulation.
Align one side of a straightedge with the two cut marks. Pull the pencil along the straightedge to provide a reference line for the cut.
Move the insulation board to place the cut line over one side of the work surface.
Set the blade of a handsaw at one side of the insulation, aligned with the cut line. Tilt the saw to set the blade at a 45 degree angle to the surface of the board. Cut along the reference line using rapid back and forth movements with the handsaw while pulling gently along the cut line.