Wall Cap vs Roof Cap: Which to Use for a Vent

When a vent has to exit the building, you usually have a choice: terminate through an exterior wall or up through the roof. As a default, a wall cap is simpler, easier to keep weathertight, and easier to service, so it is what I reach for whenever the duct can reasonably get to an outside wall.

Why a wall cap is usually the better default

A wall cap means no roof penetration to flash and re-flash, it is reachable from a ladder for cleaning, and gravity is on your side for draining any condensation outward. For most bathroom, dryer, and many range hood runs, getting to an exterior wall gives the cleanest, lowest-maintenance result.

When a roof cap makes more sense

Sometimes the fixture sits in the middle of the house with no practical path to an outside wall, an interior bathroom or an island range hood, for example. Then a roof cap is the right call. In the Sea to Sky, a roof termination needs careful placement and proper flashing so snow load and wind-driven rain cannot track in around it.

What to check

• Is there a reasonable, short path to an exterior wall? If so, favour a wall cap.
• Does the cap have a working backdraft damper so it closes when the fan is off?
• Is it sealed and flashed into the wall or roof assembly, not just screwed over a hole?
• For range hoods, is the cap sized for the hood’s airflow and free of fine grease-clogging mesh?

Common mistakes

• Forcing a long, winding run just to reach a wall when a roof cap would be far shorter.
• Roof caps installed without proper flashing, which leak in heavy weather.
• Caps with no damper, turning the vent into an open hole in the building.

When to call a sheet metal contractor

If you are planning a renovation, re-siding, or a new roof, that is the moment to place and seal terminations properly. I route the duct to the right cap for the situation and flash it into the assembly so it stays weathertight.