Roof Sailing Roof Ventilation and Attic Systems 1 — Questions and Answers
Question 1: What is the minimum net free ventilation area required per square foot of attic floor space under the IRC?
- 1/100 of floor area
- 1/150 of floor area
- 1/300 of floor area (Correct answer)
- 1/500 of floor area
Correct answer: 1/300 of floor area
The IRC requires a minimum of 1/150 of the attic floor area in net free ventilation area when vapor retarder is absent, or 1/300 when a vapor retarder is present on the warm side of the insulation.
Question 2: What is the benefit of a balanced ventilation system (equal intake and exhaust) in a residential attic?
- Reduces cooling costs only
- Creates consistent airflow that removes heat and moisture without short-circuiting (Correct answer)
- Eliminates the need for insulation
- Prevents ice dams on south-facing slopes only
Correct answer: Creates consistent airflow that removes heat and moisture without short-circuiting
A balanced system with equal intake (soffit/eave) and exhaust (ridge/upper) vents creates continuous airflow that flushes out heat in summer and moisture-laden air in winter without drawing from unintended paths.
Question 3: Where should intake vents be located in a properly designed attic ventilation system?
- At the ridge only
- At or near the eaves or soffits (Correct answer)
- At gable ends only
- At the center of the roof slope
Correct answer: At or near the eaves or soffits
Intake vents must be located at the lowest possible point — at the eaves or soffits — so that cool outside air enters at the bottom and warm, moist air exits at the ridge through exhaust vents.
Question 4: What problem can occur when attic insulation blocks soffit intake vents?
- Increased fire risk
- Reduced ventilation causing moisture buildup and heat accumulation (Correct answer)
- Structural roof damage from weight
- Increased shingle reflectivity
Correct answer: Reduced ventilation causing moisture buildup and heat accumulation
When insulation blocks soffit vents, intake airflow is eliminated, causing heat and moisture to accumulate in the attic, which can lead to ice dams, shingle deterioration, and mold growth.
Question 5: What device is installed at the soffit to maintain the airway between attic insulation and the roof deck?
- Rafter tie
- Baffle (insulation dam / rafter vent) (Correct answer)
- Vapor barrier
- Radiant barrier
Correct answer: Baffle (insulation dam / rafter vent)
Baffles (rafter vents or insulation dams) are channels installed between rafters at the eaves to keep the ventilation path open and prevent insulation from blocking the airflow from soffit vents.
Question 6: Which type of ridge vent performs best in high-wind conditions?
- Open-cut ridge without cap
- External baffle ridge vent (Correct answer)
- High-profile hip-style vent
- Static box vent near the ridge
Correct answer: External baffle ridge vent
External baffle ridge vents have a low-profile design with baffles that deflect wind over the vent opening, using the Bernoulli effect to enhance exhaust airflow rather than driving rain into the attic.
Roof Sailing Roof Ventilation and Attic Systems 1
What is the minimum net free ventilation area required per square foot of attic floor space under the IRC?