When does closing a ridge vent make sense, and how is it done?
Short answer. Closing a ridge vent makes sense mainly when the attic is being converted to a sealed, unvented assembly with spray foam, or when the roof is switching to a different exhaust plan. In a normal vented attic, closing the ridge vent removes the exhaust and invites heat and moisture problems; it is not a seasonal adjustment.
Good reasons to close one
- Spray foam conversion. An unvented attic must be airtight at the roof deck, so the ridge slot is closed and decked over as part of the design.
- Switching exhaust types. If a roof will use box vents or a fan instead, the ridge vent should be closed so the two do not short circuit.
- Persistent leaks from a failed vent. Usually the better fix is a new baffled vent, but closing is an option if ventilation is provided elsewhere.
Bad reasons
- Trying to keep the attic warmer in winter. Ventilation keeps the deck dry; closing it traps moisture.
- Hearing wind at the ridge or smelling outdoor air in the attic.
- Covering it from inside the attic with plastic or foam board. That traps condensation against the decking and can rot it.
How it is done properly
- Remove the ridge cap and the old vent.
- Install new decking strips over the slot, fastened to framing or blocking, so the deck is continuous.
- Cover with underlayment and a strip of self adhered membrane along the ridge.
- Install standard hip and ridge cap shingles.
- Confirm the attic now has another approved ventilation plan, or meets the unvented attic requirements.
Learn more about the trade-offs in roof ventilation basics and ridge vent vs box vents.