How far above the roof must a vent terminate?

How far above the roof must a vent terminate?

• A. 100 mm / 4 inches
• B. 120 mm / 5 inches
• C. 200 mm / 8 inches
• D. 150 mm / 6 inches

Answer: (D)

The key idea is that a vent must extend a minimum distance above the roof to keep vent gases from being drawn back into the building and to prevent water, snow, or debris from entering the vent opening. A standard minimum often used in practice is six inches (150 mm) above the roof surface. This height provides a clear path for vented air to escape and reduces the risk of rain or snow entering the vent when weather runs off the roof. Choosing 150 mm / 6 inches aligns with this common requirement. The smaller distances (around 100–120 mm) aren’t enough to reliably prevent water entry or blockages, while a much larger height (like 200 mm) isn’t typically required and can be unnecessarily difficult to install or service in some roof layouts.

The key idea is that a vent must extend a minimum distance above the roof to keep vent gases from being drawn back into the building and to prevent water, snow, or debris from entering the vent opening. A standard minimum often used in practice is six inches (150 mm) above the roof surface. This height provides a clear path for vented air to escape and reduces the risk of rain or snow entering the vent when weather runs off the roof.

Choosing 150 mm / 6 inches aligns with this common requirement. The smaller distances (around 100–120 mm) aren’t enough to reliably prevent water entry or blockages, while a much larger height (like 200 mm) isn’t typically required and can be unnecessarily difficult to install or service in some roof layouts.