Common Mistakes in Mixed Ventilation

Ridge vent, tall vent, turbo vent, pot vent; with so many vent choices out there, it’s hard to know which ones to choose. At Canplas®, we recommend selecting only one type of vent for your rooftop.


Installing the wrong number of vents

So how do you know if you’re selecting the right type of vent? It’s important to ensure that you’re not short circuiting your ventilation system. This means first calculating the amount of ventilation you will need.

With mixed ventilation, your vents might end up pulling from each other instead of from the soffits. This can be prevented with the right number of the same type of vents.


Using mixed ventilation

“If you have a tall vent that has a larger net free area, it’s going to draw from your roof vent that has a smaller net free area, instead of your soffits. All that they’re doing is exchanging air and your shingles are going to deteriorate.”

Donna Burtch, Duraflo® product manager, Canplas®


Roof vents can draw air from other vents when using mixed ventilation, resulting in uncirculated moist air cumulating in the soffits.

The net-free area is the range in your attic that the roof vent will be drawing air from.

Without proper ventilation, a rooftop will start to build up moisture or damage from the sun, resulting in curled-up roof shingles, ice damming, and mold.

Burtch noted that if your vents are all the same, and you have the right number of vents, you will draw from the soffits instead of from each other.

It’s important to take into account a combination of roof pitch, attic size, and climate when selecting your roof vents. We go into more detail on how to select the correct roof vent for your application here.

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