How to Check Attic Ventilation

Attics need to breathe. When they don’t, bad things happen—ice dams in winter, mold year-round, and roofs that fail years before they should. The fix is usually simple, but you have to know what you’re looking at.

Why This Matters

Your attic should stay close to outdoor temperature. Without proper ventilation:

• Summer heat builds up – Radiates into living space, overworks AC
• Winter moisture gets trapped – Condenses on cold surfaces, feeds mold growth
• Ice dams form – Warm attic melts snow, water refreezes at eaves
• Shingles cook from below – Shortens roof life by years
• Wood framing rots – Moisture destroys structural members

A well-ventilated attic protects your roof, your energy bills, and your air quality.

The Basic Principle

Attic ventilation works on simple physics: cool air enters low, warm air exits high. You need both intake and exhaust for air to move.

• Intake vents – Soffit vents under the eaves let fresh air in
• Exhaust vents – Ridge vents, gable vents, or powered fans let hot air out

Both are required. One without the other doesn’t work.

What to Check

1. Soffit Vents (Intake)

Look at the underside of your eaves from outside, then check from inside the attic:

• Are the vents visible and unobstructed?
• Is insulation blocking airflow from inside?
• Are they covered in dust or painted over?

Blocked intake is the most common problem. Insulation contractors often push batts right against the soffits, cutting off airflow.

2. Ridge or Roof Vents (Exhaust)

From inside the attic, look up at the peak:

• Can you see daylight through ridge vents?
• Are they clear of debris, dust, or insulation?
• Is there a continuous opening along the ridge?

From outside, check that ridge vents aren’t covered by leaves or debris.

3. Gable Vents

These are the rectangular vents on the side walls of your attic:

• Are they open and not blocked by stored items?
• Screens intact (no pest entry)?
• Not painted shut?

4. Attic Fans (If Present)

Some homes have powered fans:

• Does the fan spin when the attic is hot?
• Is the thermostat set correctly (around 100-110°F)?
• Is the fan clean and unobstructed?

The Rule of Thumb

Building codes recommend 1 square foot of net free ventilation per 150 square feet of attic space. Split between intake and exhaust—roughly half each.

To check: Measure your attic floor area. Divide by 150. That’s your target ventilation in square feet. Compare to what you see.

Warning Signs of Problems

• Shingles curling or failing prematurely
• Ice dams forming along eaves in winter
• Excessive heat in second-floor rooms
• Musty smell in attic or upstairs
• Dark streaks on roof decking (mold)
• Rusty nails poking through roof boards
• Wet or compressed insulation

Any of these means it’s time for a closer look or professional help.

DIY vs. Call a Pro

DIY: Visual inspection, clearing obvious blockages, ensuring soffit baffles are in place.

Call a pro: Calculating proper ventilation, installing new vents, adding ridge vent, repairing roof damage from poor ventilation. Find a roofing contractor →

How Often to Check

• Quick check: Once a year, preferably in fall before winter
• Full inspection: When replacing roof, adding insulation, or seeing warning signs

The Bottom Line

Attic ventilation isn’t exciting, but it’s one of those invisible systems that determines how long your roof lasts and how comfortable your home feels. A half-hour in the attic once a year can catch problems before they become expensive repairs.