What clearance is needed between the bottom of the roof sheathing and the insulation for a cornice vent?

What clearance is needed between the bottom of the roof sheathing and the insulation for a cornice vent?

• A. 1 inch
• B. 2 inch
• C. 1/2 inch
• D. 3 1/2 inch

Answer: (A)

For cornice ventilation to work, there must be an unobstructed air path from the soffit into the attic at the eave. That means the insulation should not sit right up against the bottom of the roof sheathing where the vent opens. A one-inch clearance keeps a continuous air channel open so air can flow into the cornice vent without being blocked by insulation. If the space were smaller, insulation could block the vent and reduce ventilation, leading to moisture buildup, condensation, or rot. The other numbers don’t fit the purpose of maintaining an open air path—their values either relate to insulation thickness or exceed what’s needed for the vent’s air intake. So maintaining a one-inch gap is the correct approach.

For cornice ventilation to work, there must be an unobstructed air path from the soffit into the attic at the eave. That means the insulation should not sit right up against the bottom of the roof sheathing where the vent opens. A one-inch clearance keeps a continuous air channel open so air can flow into the cornice vent without being blocked by insulation.

If the space were smaller, insulation could block the vent and reduce ventilation, leading to moisture buildup, condensation, or rot. The other numbers don’t fit the purpose of maintaining an open air path—their values either relate to insulation thickness or exceed what’s needed for the vent’s air intake. So maintaining a one-inch gap is the correct approach.