Mixed Roofing Ventilation Products on Your Roof

Roof of house - depicting roofing ventilation

When it comes to roofing ventilation, most homeowners don’t know a lot about what types there are. Unless you have had a bad experience with inadequate ventilation you are probably content to let your roof and attic do their thing.

However, what if it comes to a choice, or you have someone telling that you need to change or add attic ventilation?

Should you mix the types of ventilation?

Roofing Ventilation 101

The ideal attic ventilation system is a balanced one and a passive one. This means that no air is actually being blown anywhere. The system relies on the natural movements of hot and cold air to make the air in your attic the right temperature.

In order to achieve this system of balance, you need the correct number of intake vents (usually installed in the soffit or under your eaves) and exhaust vents (installed at or near your roof’s peak).

If the roof ventilation system is out of balance, you are going to start having problems. This includes skyrocketing energy bills, ice dams, and roof deterioration among other things. In addition, mold could grow down into your walls where you can’t see it.

This problem has less to do with excess heat trapped in your attic than it does with the moisture problem created by inadequate ventilation.

One problem we see with ventilation is that contractors haven’t installed enough intake vents or none at all. It is more time-consuming to install a vent under an eave than to just slap a new roof onto the top of the structure and call it a day.

In order for a roof to last, it has to have intake ventilation. In fact, it’s better to err on the side of too much intake rather than too much exhaust. Some of those intake panels can actually act as exhaust panels when they are on the leeward side of the house, sheltered from the wind.

Mixed Exhaust Ventilation

The other question about ventilation you might run into is whether you should install a turbine vent if you already have a ridge vent or vice versa. By the way, this would be very rare, as ridge ventilation actually requires a structural change other than cutting a hole and installing the vent.

Two Roofing Ventilation Products Are Not Better Than One

More does not equal better when it comes to attic ventilation. Again, the thing you are going for is not just letting out heat during the summer months. It is actually regulating temperature and moisture levels.

When you add another kind of ventilation exhaust system to the one you already have, the two (or more) actually end up competing with each other and lowering the performance of the whole system.

Air follows the path of least resistance. In a well-designed system the air will flow from the intake vents up to the exhaust vents and flush out the warm, moist air along the entire underside of the roof decking in the process.

A secondary exhaust vent interrupts the flow of the air. In fact, sometimes even to the extent that it will become like a secondary intake vent for the primary exhaust vent. This leaves large parts of the attic space “dead” and inadequately vented.


If you are having problems with your roofing ventilation and someone tells you that you need to add another exhaust vent, think again. Correctly installed roofing ventilation will create lots of intake ventilation with one source of exhaust ventilation.

If you live in the Southeast Michigan area, please give us a call. We would be happy to help.

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