How to Cut a Hole in a Roof for Ducting

Climb up into the attic space and locate the roof area above the duct. Measure the width of the area between the two roof trusses using a tape measure. Divide the number in half to locate the center of the area, and draw a pencil mark in it.

Insert the tip of a 5- to 6-inch spike on top of the pencil mark, and hammer it up through the roof until it extends out the top. If desired, you can accomplish the same process using a drill and a 5- to 6-inch drill bit.

Measure the diameter of the duct using the tape measure to determine the diameter of the required hole. If you are installing a vent or fan, refer to the manufacturer’s instructions for the proper-sized hole opening.

Walk to the exterior of the home, and use a ladder to climb up onto the roof. Walk to the general area where you are installing the duct hole, and look closely at the roof until you locate the nail head. When you locate the nail, tap it with a hammer to sink it back inside the home.

Divide the diameter of the circular opening in half to arrive at the radius, and then add 1 inch. Cut a piece of string to the length, and then tie the last inch of it around a piece of chalk. Place the free end of the string on top of the nail hole. Swing the chalk end around in a circle to draw your cut line on the roof.

Run a utility knife around the chalk line to cut through the roofing material and the tar paper. Insert a pry bar up under the shingles to pull out the nails and detach the shingles within the circular area.

Cut out the remaining plywood using a reciprocating saw to cut around the circular perimeter.