Why Ventilation Matters

Proper attic ventilation is critical for roof longevity and home comfort. It removes heat in summer (reducing cooling costs) and moisture in winter (preventing ice dams, mold, and rot).

Benefits of Proper Ventilation:

• Extends shingle lifespan by 5-10 years
• Prevents ice dams in winter
• Reduces cooling costs in summer
• Prevents mold and rot in attic
• Required by building code and shingle warranties

Consequences of Poor Ventilation:

• Premature shingle failure (curling, cracking)
• Ice dams and water damage
• Mold growth in attic
• Rot in roof deck and rafters
• Voided shingle warranties

The 1:300 Rule

Building Code Requirement:

1 square foot of net free ventilation area (NFA) per 300 square feet of attic floor space.

Example Calculation:

• Attic floor: 1,500 sq ft
• Required NFA: 1,500 ÷ 300 = 5 sq ft
• Intake (soffit): 2.5 sq ft
• Exhaust (ridge/gable): 2.5 sq ft

Balanced System:

50% intake (soffit vents) + 50% exhaust (ridge/gable vents). Imbalanced systems don't work properly.

Ventilation Types

Intake Ventilation (Bottom of Roof):

• Soffit Vents: Continuous or individual vents in eave soffits (REQUIRED)
• Drip Edge Vents: Ventilated drip edge (alternative to soffit vents)

Exhaust Ventilation (Top of Roof):

• Ridge Vents: Continuous vent along ridge (BEST option)
• Gable Vents: Vents in gable ends (OK, but less effective than ridge)
• Roof Vents: Individual vents on roof slope (OK for spot ventilation)
• Turbine Vents: Spinning vents (effective but noisy)
• Power Vents: Electric fans (expensive to operate, not recommended)

Before You Start

Skill Level: Intermediate

Time Required: 1-2 days for complete system

Cost: $500-1,500 (DIY) vs. $1,500-3,000 (professional installation)

Required Tools

• Reciprocating saw or jigsaw (for cutting roof deck)
• Circular saw (for cutting ridge)
• Drill with bits
• Utility knife
• Tape measure
• Chalk line
• Pry bar
• Hammer or roofing nailer
• Caulk gun

Materials Needed

• Ridge vent (length of ridge)
• Soffit vents (continuous or individual)
• Roof vents (if needed for additional exhaust)
• Roofing nails
• Roofing cement
• Ridge cap shingles
• Baffles (to prevent insulation from blocking soffit vents)

Step 1: Calculate Ventilation Requirements

Process:

1. Measure attic floor: Length × width = square footage
2. Calculate required NFA: Attic sq ft ÷ 300 = NFA needed
3. Divide 50/50: Half intake, half exhaust
4. Select products: Check manufacturer specs for NFA per unit
5. Calculate quantity: Required NFA ÷ NFA per unit = quantity needed

Step 2: Install Soffit Vents (Intake)

Why This Matters:

Soffit vents provide intake air. Without adequate intake, exhaust vents can't function properly.

Continuous Soffit Vents (Recommended):

1. Remove existing soffit: If replacing solid soffit
2. Cut soffit to size: Measure and cut ventilated soffit panels
3. Install panels: Nail or screw to fascia and wall
4. Ensure airflow: Verify vents aren't blocked by insulation

Individual Soffit Vents:

1. Mark vent locations: Evenly spaced along soffit
2. Cut openings: Use jigsaw or hole saw
3. Install vents: Screw or nail in place
4. Seal edges: Caulk around vent perimeter

Install Baffles (Critical):

1. Position baffles: Between rafters at eaves
2. Staple to deck: Secure to roof deck
3. Ensure airflow path: From soffit to ridge, unobstructed
4. Keep insulation back: Don't let insulation block airflow

Step 3: Install Ridge Vent (Exhaust - Recommended)

Why Ridge Vents Are Best:

• Continuous ventilation along entire ridge
• Natural convection (hot air rises)
• No moving parts (no maintenance)
• Weather-resistant design
• Aesthetically pleasing (low profile)

Installation:

1. Remove ridge cap shingles: Along entire ridge
2. Snap chalk lines:
   • 1 inch from ridge center on each side
   • Creates 2-inch wide slot
3. Cut ridge deck:
   • Use circular saw set to deck thickness
   • Cut along chalk lines
   • DO NOT cut through ridge board (structural)
   • Stop cuts 6 inches from each end of ridge
4. Remove cut deck: Pry out cut section
5. Position ridge vent: Center over opening
6. Nail ridge vent: Follow manufacturer instructions (typically every 12 inches)
7. Install ridge cap shingles: Over ridge vent, following manufacturer specs

Step 4: Install Roof Vents (If Needed)

When to Use Roof Vents:

• Hip roofs (no ridge to vent)
• Additional exhaust needed
• Spot ventilation for problem areas

Installation:

1. Mark vent location: High on roof slope, near ridge
2. Remove shingles: 12 inches around vent location
3. Cut opening: Use reciprocating saw or jigsaw
4. Position vent: Center over opening
5. Nail vent flange: To roof deck
6. Reinstall shingles: Over vent flange (top and sides), under flange (bottom)
7. Seal edges: Roofing cement under shingle edges

Step 5: Install Gable Vents (Alternative Exhaust)

When to Use Gable Vents:

• No ridge vent
• Gable-style roof
• Supplement to ridge vent

Installation:

1. Mark vent location: High on gable end, near ridge
2. Cut opening: Use reciprocating saw
3. Frame opening: 2x4 framing around opening
4. Install vent: Screw or nail to framing
5. Seal edges: Caulk around vent perimeter

Step 6: Verify Balanced System

Critical Check:

1. Calculate total intake NFA: Add up all soffit vent NFA
2. Calculate total exhaust NFA: Add up all ridge/roof/gable vent NFA
3. Verify 50/50 balance: Intake and exhaust should be approximately equal
4. Adjust if needed: Add vents to balance system

Fraser Valley Specific Considerations

Winter Moisture:

• Adequate ventilation prevents condensation in attic
• Condensation leads to mold, rot, and ice dams
• Ensure continuous airflow from soffit to ridge

Summer Heat:

• Attic temperatures can reach 150°F+ without ventilation
• Heat accelerates shingle aging
• Ventilation reduces attic temperature by 20-40°F

Ice Dams:

• Proper ventilation keeps roof deck cold
• Cold deck prevents snow melt and ice dam formation
• Combine ventilation with proper insulation (R-50)

Common Mistakes to Avoid

1. Imbalanced System

Too much exhaust, not enough intake (or vice versa). System won't work properly.

2. Blocked Soffit Vents

Insulation pushed into eaves blocks airflow. Use baffles to maintain airflow path.

3. Mixing Exhaust Types

Using ridge vents AND gable vents creates short-circuiting (air flows from soffit to gable, bypassing ridge). Choose one exhaust type.

4. Inadequate Ventilation

Not meeting 1:300 rule. Insufficient ventilation causes all the problems you're trying to prevent.

5. Power Vents

Electric fans are expensive to operate and can create negative pressure that pulls conditioned air from living space. Not recommended.

Maintenance

Annual Inspection:

• Check soffit vents for blockages (paint, debris, wasp nests)
• Inspect ridge vent for damage or separation
• Verify baffles are in place and not crushed
• Check attic for signs of moisture (condensation, mold, frost)

The Bottom Line

Proper ventilation is critical for roof longevity and home comfort. The 1:300 rule is a minimum — more ventilation is better. Balanced intake and exhaust is essential.

At RJ Roofing Bros, we install balanced ventilation systems on every roof. Ridge vents with adequate soffit intake. Baffles to maintain airflow. We verify the 1:300 rule is met. Proper ventilation is included in our standard installation — not an upsell.

Need ventilation installed or upgraded? Call (604) 997-1292 for a free assessment.