Which type of roof vent is best?
Continuous ridge vent, balanced against soffit intake, for almost every pitched shingle or metal roof. It exhausts along the whole ridge where the hot air already is, has no moving parts and no power, and adds no penetration to the field. Our published rate to cut one in is $15 per foot.
The five exhaust vents, compared
| Type | How it works | Where it fails |
|---|---|---|
| Continuous ridge vent | A slot cut along the ridge, covered by a baffled vent and shingled over. Exhausts along the whole length where the hot air already collects. | Cheap unbaffled versions let wind-driven rain and snow in. Installed without enough intake it does very little. |
| Box or louvre vents | Individual square vents cut into the field near the ridge. Cheap and simple. | Each one is a hole in the field of the roof, so each one is a flashing detail that can leak. They exhaust only the area around themselves. |
| Turbine, or whirlybird | A wind-driven spinning cowl that pulls air out mechanically. | Only works when the wind blows, has bearings that fail and squeak, and can pull conditioned air out of the house through ceiling gaps. |
| Powered attic fan, electric | A thermostat-controlled fan that forces air out. | Uses power, has a motor to fail, and if the attic intake is inadequate it pulls make-up air from the house — pulling your air conditioning into the attic. |
| Solar-powered attic fan | The same thing driven by a small photovoltaic panel. | Same short-circuit risk without adequate intake, plus a panel and a battery to age. Runs when the sun shines, which at least matches when the heat is worst. |
Intake, which is the half nobody asks about, is normally continuous soffit vent or individual soffit louvres, with baffles at the eaves so insulation cannot block the airflow. On houses with no soffit at all, edge intake vents fitted at the eave course are the retrofit answer, and they are worth doing — an exhaust-only attic is a common and expensive mistake.
Why mixing vent types makes ventilation worse
The single most common ventilation defect on a re-roof is a new ridge vent installed while the old box vents are left in place. Air follows the path of least resistance, so instead of drawing across the whole attic from soffit to ridge, the ridge vent pulls its make-up air from the nearest box vent a few feet below it. The result is a short circuit: a small loop of air moving near the ridge and a stagnant attic everywhere else.
The same applies to a powered fan alongside a passive ridge vent — the fan simply sucks air back down through the ridge. When a ridge vent goes on, the old field vents are removed and the holes are decked and shingled over. If a quote does not say so, ask.
More vents is not more ventilation. A single continuous path from the soffits to the ridge moves more air than five products competing with each other.
If the soffits are blocked, adding exhaust does nothing except add penetrations. The measurement that matters is net free area at intake against exhaust, and it takes ten minutes in the attic to work out.
Ask instead: What is the intake net free area at the soffits, and what is the exhaust? Show me the two numbers.A powered fan in an attic with inadequate intake pulls conditioned air out of the house through every ceiling penetration, so you pay to cool the attic with your own air conditioning. Powered ventilation has legitimate uses; it is not a substitute for intake.
Ask instead: Where is the make-up air coming from if you install this?Roof vent questions
Are ridge vents better than box vents?
On almost any pitched roof with a usable ridge, yes. A continuous ridge vent exhausts along the entire ridge line where hot air already collects, and it adds no penetration to the field of the roof because it sits under the cap shingles. Box vents only exhaust the area immediately around themselves and each one is an individual hole with its own flashing detail. Box vents remain the practical answer on hip roofs with very little ridge, and on sections where a ridge vent cannot be run.
Do powered attic fans work?
They move air, and whether that helps depends entirely on where the make-up air comes from. In an attic with generous soffit intake, a powered fan does what it says. In an attic with blocked or insufficient intake — which is most older houses — the fan takes the easiest available air, which is conditioned air pulled out of the house through gaps around light fittings and the loft hatch. You then pay to cool the attic with your own air conditioning. Fix intake first, then decide whether a fan is needed at all.
Do solar roof vents work?
They work on the same principle as an electric powered fan, without the wiring and without the running cost, and they run hardest when the sun is strongest, which is when the attic needs it. The same caution applies: without adequate intake at the soffits a solar fan short-circuits and pulls conditioned air from the house. They also carry a panel, a motor and sometimes a battery, all of which age faster than a passive vent with no moving parts.
How many roof vents does a house need?
It is calculated as net free area rather than counted as units. Take the attic floor area, divide by 300 for a balanced system, and multiply by 144 to get square inches. Split it at least 40 percent intake at the soffits and the rest as exhaust near the ridge. Then read the net free area printed on the vent you are using and work out how many that takes. A continuous ridge vent commonly provides around 18 square inches per linear foot; a box vent typically provides between 50 and 60 square inches each.
Can you have a ridge vent and box vents together?
You can physically, and it is the most common ventilation defect on a re-roof. The ridge vent draws its make-up air from the nearest box vent instead of from the soffits, so the air loops around the top of the roof and the rest of the attic stays stagnant. When a ridge vent is installed the old field vents should be removed and the openings decked and shingled over. If a quote for a new roof with ridge venting does not mention removing the existing vents, ask what is happening to them.
Do metal roofs need vents?
Yes, the same requirement applies, and the products differ. Standing-seam metal roofs use a purpose-made metal ridge vent with a closure that seals to the panel profile, and the intake is at the eave the same way. Because a metal roof is often installed over a solid deck with a high-temperature underlayment, the ventilation path under the panel and above the deck matters, and on some assemblies a batten system creates a deliberate air gap. It is a design decision on a metal roof rather than an afterthought.
Where to go next
Vents are the products. These cover the requirement and the balance they have to satisfy.
Roof ventilation requirements and the code calculation
Why ventilation is necessary, the net free area arithmetic, and what it costs.
Read the guide →VentilationAttic ventilation: intake, exhaust and balance
How much net free area an attic needs, and the damage done by too much exhaust or a blocked soffit.
Read the standard →WarrantyWhat a roof warranty actually covers
The two separate warranties on every roof, and the exclusions that surprise homeowners.
Read the standard →ThesisWhy a roof fails at its details, not its field
Roofs rarely fail in the middle of a plane. They fail at edges, valleys, walls and penetrations.
Read the standard →