Crew is doing a reroof on a 1,900 sq ft ranch.

Short-circuiting the airflow. You’ve created competing exhaust points. Ridge vents rely on the stack effect: cool air enters low (soffits), warms, and exits high (ridge). By leaving the turtle vents and gable louvers, you give that rising hot air easier, lower exit paths. The ridge vent becomes ineffective; the attic ventilates only the upper third, leaving heat trapped at the sheathing.

Code violation. IRC R806.2 requires cross-ventilation or a balanced system. Mixing exhaust types without disabling the old ones unbalances the system. Most ridge-vent manufacturers (Air Vent, GAF, CertainTeed) explicitly void warranties if other exhaust vents remain active.

Fix:

1. Remove turtle vents; sheath and flash the holes.
2. Block gable louvers from inside (rigid foam + tape) or remove and side over.
3. Verify soffit intake: 1 sq ft Net Free Area (NFA) per 150 sq ft attic floor (IRC R806.2). For 1,900 sq ft, you need ~12.7 sq ft NFA intake and 12.7 sq ft NFA exhaust. A typical 4-ft ridge vent strip provides ~72 sq in NFA/ft; you’ll need ~25 linear feet of ridge vent.
4. Ensure baffles keep insulation off soffits.

If the foreman argues “more vents = better,” he’s wrong. One high exhaust + low intake = flow. Multiple exhausts = stagnation.

The foreman’s plan to add a full-length ridge vent while leaving the existing turtle vents and gable-end louvers in place creates a short-circuiting airflow problem — a common and serious mistake in attic ventilation design.

What’s Wrong:

Attic ventilation relies on balanced intake and exhaust. Intake (soffit vents) brings in cool air; exhaust (ridge, gable, or turtle vents) releases hot air. For effective convection, air should flow from low (soffit) to high (ridge) along the underside of the roof deck.

By retaining turtle vents (near the roof peak but not at the ridge) and gable-end louvers (on the sidewalls) in addition to a full ridge vent, you create multiple exhaust points at different heights. This disrupts the natural stack effect:

• Hot air will preferentially exit through the closest or lowest exhaust point (often the turtle vents or gable louvers), bypassing the ridge vent entirely.
• This creates dead zones in the attic where stale, hot air isn’t exhausted — especially near the ridge if the ridge vent is “starved” of makeup air due to competing exhausts.
• Worse, if wind blows into a gable louver, it can reverse flow, pushing hot air into the attic instead of out — turning exhaust into intake and causing short-circuiting: air enters soffit, exits immediately via nearby gable/turtle vent, never circulating through the attic volume.

Code Reference:

Per IRC R806.2 (2021/2024), attic ventilation must provide uniform airflow to prevent moisture buildup and heat retention. The code implies balanced, unobstructed paths from intake to exhaust — not competing exhausts that disrupt stratification.

Correct Approach:

• Remove the turtle vents and gable louvers when installing a full ridge vent.
• Ensure soffit intake is unobstructed (baffles installed, insulation pulled back).
• Ridge vent should be the sole exhaust, working with soffit intake for continuous, laminar flow.
• If gable vents are to remain, they must be sealed off (not just left open) — or the ridge vent omitted — but mixing them violates ventilation principles.

Bottom Line:

Leaving multiple exhaust types in place defeats the purpose of the ridge vent, risks inadequate ventilation, and can worsen attic heat and moisture problems. Remove the old vents. This is a standard best practice — not just opinion, but grounded in building science and code intent. If the crew refuses, consult a licensed roofing contractor or building inspector.

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