Can you have too much attic ventilation?
Short answer. In terms of vent area alone, it is hard to have too much passive attic ventilation; the code sets a minimum, not a maximum. Problems come from the wrong kind of extra ventilation: excess exhaust without matching intake, several exhaust types on one attic, powered fans, or extra holes that let in wind driven rain.
Why more passive area usually is not harmful
Passive vents only move air when wind or rising heat drives it. If you have double the minimum area in balanced intake and exhaust, air simply moves a bit more freely. The attic does not get colder than outdoors, and it does not pull heat out of the house when the ceiling is properly air sealed and insulated.
When "too much" does cause trouble
- Too much exhaust for the intake. If exhaust area far exceeds intake, the attic tends to run slightly negative and draws air from the house through ceiling gaps, carrying moisture and conditioned air with it. Many manufacturers recommend intake equal to or greater than exhaust for this reason.
- Too many penetrations. Every extra box vent or turbine is another opening to flash and another target for hail. A roof covered in vents has more places to leak.
- Wind driven rain. Low quality vents and oversized openings near the ridge can admit rain during the strong storms Georgia sees in spring and summer.
- Powered fans. A fan can easily outpull the available intake, which is the most common true over ventilation problem.
Signs your setup has gone too far
Watch for drafts at ceiling fixtures, higher cooling bills after adding a fan, water spots below vents after storms, or a roof with three different kinds of exhaust. The fix is usually to remove extra exhaust and add intake, not to add more vents. Learn more in roof ventilation basics.