How to Cut a Fascia Board at the Outside Corners
Fascia is placed on the edge of the roof, secured to the home's rafter face (the piece of wood secured to the roof joists). Fascia may be made of either vinyl or aluminum, but its installation is the same. The soffit is installed underneath the fascia. However, you do not need to replace the soffit to replace the fascia. At an outside corner, fascia must be cut and mitered along the bottom to create a tight fold.
Start from a fascia piece's left edge and measure 5 1/2 inches to the right. Mark this length near the fascia's top and bottom edge. Draw a line connecting the two marks using a straight edge. Cut along the line with a tin snips.
Measure from the bottom of the F-channel (which is the hook piece on the bottom of the rafter face) to the undersill (the top of the rafter face). Subtract 1/8 inch from this measurement.
Measure from the 5 1/2-inch piece of fascia's bottom edge up. Place a mark on the fascia indicating the height you measured in Step 2. Move down the fascia's length, placing a few more height marks. Draw a line connecting the height marks with a straight edge. Cut the fascia along the line with a tin snips.
Flip the fascia piece over and lay it face down on a flat work surface. Measure 2 3/4 inches over from the fascia's left edge, along the bottom edge and the back side. Mark this measurement on the fascia's bottom edge and draw a straight line down the fascia's back side. This is the center line of the 5 1/2-inch length of fascia.
Hold a protractor along the fascia's bottom edge, centered over the mark you made in Step 4. Make a 45-degree line on the left and right sides of the center line using the protractor. The two lines should meet at the mark from Step 4 to form a 90-degree angle.
Cut the two 45-degree lines with a tin snips to remove a small piece from the fascia's bottom edge. Hold a metal straight edge along the line you drew in Step 4. Bend the fascia over the metal straight edge until the two cuts you just made meet.
Position the fascia corner cap you just made over the rafter face's outside corner. The fascia's bottom edge hooks over the F channel on the bottom of the rafter face. Secure the fascia in place with stainless steel nails.