Arkansas HVACR NewsMagazine March 2026

HVACR NewsMagazine March 2026

Tech News

Ridge vents exhaust it up high via natural convection (with some guidance from baffles). While the wind pushes air above the roof and against its slopes, it helps create negative pressure when it blows across the ridge vent(s), forcing some attic air out. But while wind is helpful in well-designed ventilation systems, it can also cause lots of problems when we have significant leaks or poor vent designs. When wind pushes air straight into the attic via poorly placed off ridge exhaust vents or significant gaps in the structure, that air doesn’t have the same designed ventilation pathway as it would with properly planned soffit and ridge vents that follow the IRC’s guidance. Additionally, that air contains water vapor. Generally speaking, bulk water is the worst way for water to enter (as opposed to water vapor in the air or via vapor diffusion), but water vapor in the air is a definitive second- place. It also doesn’t help that wind often comes with severe (read: very wet) weather conditions. Based on the way heat and water vapor behave and the IRC’s guidance, it would make sense for a Florida home to have 60% of the attic ventilation come in via low soffit vents and 40% at ridge vents in the peaks. With that design, we can take advantage of solar radiation, convection, water vapor’s natural tendencies, and baffles to keep the fresh air on the edges of the attic and on a clear ventilation pathway — that is, away from centrally located supply ducts and air handlers. When the air in the center of the attic has no reason to move or be displaced by incoming air, there isn’t nearly as much condensation. Vent Placement: Expectation vs. Reality

Unfortunately, that’s not quite what we see a lot of the time.

Off-Ridge Vents and Crossflow

If you’ve ever seen Florida McMansions, you may have seen sections of roofing about midway up the roof that jut out — very clear off- ridge vents. Rick Sims called them “big, goofy roof caps,” and they are heavy contributors to the moisture problems we see. These vents are intended to be exhaust vents, but they’re lower than the ridge and allow large volumes of humid air to enter the unconditioned attic via wind. Even worse, their location enables crossflow; instead of staying along the edges and exiting the structure at or near the peak, humid air gets dumped into the middle of the attic and is more likely to flow across the attic, bringing its moisture with it and causing ducts to sweat between the added moisture and movement.

When we have off-ridge vents instead of ridge vents for exhaust, it’s also worth mentioning that the moisture that does reach the top just cycles. Again, when the roof decking loses heat at night, that moisture will condense