How to Put a Hole for a Vent on a Flat Roof

Attic spaces, bathrooms and kitchen exhaust hoods require a vent that dispels unwanted air to the outside. Often, the roof is the most direct route for an exhaust vent. A hole must be cut through the roof before the vent is installed. Cutting a vent hole in a flat roof offers some challenges over cutting through a standard pitched roof. A flat roof consists of multiple layers of different materials. Using the correct cutting tool allows you to cut through all the material types without stopping to change blades.

12-inch-long, 5/32-inch drill bit
Drill
Extension ladder
Vent
Pencil
Bi-metal blade
Reciprocating saw

Instructions

- 1
  Secure a 12-inch-long, 5/32-inch drill bit in a drill.
- 2
  Crawl inside the attic. Set the drill bit tip on the sheeting of the flat roof – directly above the area requiring the hole. Ensure that the hole will not sit within 2 inches of a roof truss.
- 3
  Drill through the sheathing. Continue drilling until the chuck of the drill sits against the sheathing. Loosen the drill chuck. Pull the drill down, leaving the drill bit in the roof. Set an extension ladder against the side of the house. Ensure the ladder is stable. Climb the ladder.
- 4
  Place a vent over the drill bit. Move the vent until the drill bit sits in the center of the vent opening. Pull a permanent marker along the vent’s interior opening.
- 5
  Secure a bi-metal blade in a reciprocating saw. Cut along the marked line with the reciprocating saw. Be careful not to cut through the sheathing. Pull the drill bit from the roof. Pull the membrane and insulation from the hole. Cut through the sheathing. Remove the wood from the hole.

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