How can you tell if you have a ridge vent, and whether it is actually working?
Short answer. From the yard, a ridge vent shows as a slightly raised, continuous ridge cap with small dark openings at each end; from the attic, you will see a strip of daylight along the peak where the deck was cut back. If the ridge looks vented from outside but there is no daylight slot from inside, the vent may have been installed without the slot being cut, which means it does nothing.
Check 1: from the yard
- Look along the ridge with binoculars. A vented ridge sits a bit higher than a plain cap and runs the full length evenly.
- Look at the ridge ends from the side. Many vents show a small dark gap or a plug under the end cap.
- Older homes may have an aluminum ridge vent with visible metal louvers instead.
Check 2: from the attic
- Go up on a bright day and turn off the attic light.
- Look at the peak. A ridge vent slot shows as a continuous line of light between the two sides of the deck.
- Note where it stops. It should end short of the gable ends and walls, but not stop after a few feet.
Check 3: the slot that was never cut
It happens: a ridge vent goes on during a reroof, but the slot is not cut, or is cut only partway, or the crew left the old felt over it. From outside it looks vented. From inside there is no light. Similarly, a slot can be covered by later decking or spray foam.
Check 4: competing vents
If you have a ridge vent plus box vents, a turbine or a fan, the ridge vent may be working backward, pulling air in. Ideally the attic has one exhaust type.
For what a working ridge vent needs, see ridge vent vs box vents and roof ventilation basics.