The Hidden System That Extends Your Roof's Lifespan

Proper roof ventilation can add 5-10 years to your shingles' lifespan. Improper ventilation can cut it in half. Yet most homeowners never think about it, and many contractors don't calculate it correctly.

Ventilation isn't sexy. It's not visible. It doesn't have curb appeal. But it's critical to your roof's performance, your home's energy efficiency, and your comfort.

This guide explains what roof ventilation is, why it matters in Fraser Valley's climate, and how to ensure your roof is properly ventilated.

What Is Roof Ventilation?

Roof ventilation is the system that allows air to flow through your attic space, entering at the eaves (soffits) and exiting at or near the ridge. This continuous airflow:

• Removes Heat: Prevents attic temperatures from exceeding 70°C in summer
• Removes Moisture: Prevents condensation and mold growth in winter
• Extends Shingle Life: Reduces thermal cycling stress on shingles
• Prevents Ice Dams: Keeps roof deck cold in winter (prevents snow melt and refreezing)
• Improves Energy Efficiency: Reduces cooling costs in summer

The Science: How Ventilation Works

The Stack Effect (Natural Convection):

Hot air rises. In an attic, hot air accumulates at the peak. If there's an exit point (ridge vent, gable vent, etc.), hot air escapes. This creates negative pressure, pulling cooler air in through soffit vents at the eaves.

The Balanced System:

For ventilation to work, you need:

• Intake Vents: At eaves (soffit vents) — 50% of total ventilation area
• Exhaust Vents: At or near ridge (ridge vents, gable vents, etc.) — 50% of total ventilation area

The 1:300 Rule (Building Code):

BC Building Code requires 1 square foot of net free ventilation area (NFA) for every 300 square feet of attic floor space, with balanced intake and exhaust.

Example:

• 1,500 sq ft attic floor = 5 sq ft NFA required
• 2.5 sq ft intake (soffit vents)
• 2.5 sq ft exhaust (ridge vent or equivalent)

Types of Ventilation Systems

1. Ridge Vents (Our Preferred Exhaust System)

What It Is:

Continuous vent running along the entire roof ridge, covered by a cap that allows air to escape while keeping rain and snow out.

Advantages:

• Even Exhaust: Vents entire ridge length, not just a few points
• Aesthetics: Low-profile, blends with roof
• No Moving Parts: Passive system, no maintenance
• Works with Soffit Vents: Creates ideal balanced system

Installation:

• 1-2 inch slot cut along ridge
• Ridge vent installed over slot
• Ridge cap shingles installed over vent

Cost: $3-5 per linear foot installed

Our Recommendation: Ridge vents are the gold standard for exhaust ventilation. We install them on 90% of our projects.

2. Soffit Vents (Essential Intake System)

What It Is:

Vents installed in the soffit (underside of roof overhang) that allow air to enter the attic at the eaves.

Types:

Continuous Soffit Vents:

• Perforated strips running entire soffit length
• Best option for new construction or soffit replacement
• Provides maximum intake area

Individual Soffit Vents:

• Circular or rectangular vents spaced along soffit
• Easier to retrofit on existing soffits
• Requires proper spacing calculation

Critical Rule: Soffit vents must not be blocked by insulation. Baffles (rigid foam or cardboard channels) should be installed between rafters to maintain airflow path from soffit to ridge.

3. Gable Vents (Supplemental Exhaust)

What It Is:

Louvered vents installed in gable ends (vertical walls at roof peaks).

Advantages:

• Good for cross-ventilation
• Aesthetically pleasing (can be decorative)
• Works well in combination with soffit vents

Limitations:

• Only ventilates attic ends, not entire space
• Less effective than ridge vents for even airflow
• Can create short-circuit airflow if combined with ridge vents

Our Recommendation: Gable vents are fine as supplemental ventilation but shouldn't be the primary exhaust system. Ridge vents are more effective.

4. Turbine Vents (Wind-Powered Exhaust)

What It Is:

Spinning metal vents that use wind to pull air out of the attic.

Advantages:

• Effective in windy areas (Hope, exposed Chilliwack)
• No electricity required
• Can move large volumes of air

Disadvantages:

• Moving parts can fail (bearings wear out)
• Noisy in high winds
• Aesthetically divisive (some people hate them)
• Ineffective in calm conditions

Our Recommendation: Turbine vents work, but ridge vents are more reliable and quieter.

5. Power Vents (Electric Exhaust)

What It Is:

Electric fans that actively pull air out of the attic, often controlled by thermostats.

Advantages:

• Powerful exhaust (can move large volumes quickly)
• Thermostat-controlled (activates when attic reaches set temperature)
• Good for complex roof geometries

Disadvantages:

• Requires electricity (operating cost)
• Moving parts can fail
• Can create negative pressure that pulls conditioned air from living space
• Expensive to install and operate

Our Recommendation: Power vents are overkill for most homes. Passive ridge and soffit vents are adequate and more cost-effective.

Why Ventilation Matters in Fraser Valley

1. Summer Heat (Chilliwack, Abbotsford)

Fraser Valley summers can hit 35°C+. Without ventilation, attic temperatures can exceed 70°C. This extreme heat:

• Accelerates shingle aging (thermal cycling stress)
• Increases cooling costs (heat radiates into living space)
• Can warp roof decking
• Degrades adhesive on shingles

Proper Ventilation: Keeps attic within 5-10°C of outdoor temperature, dramatically reducing thermal stress.

2. Winter Moisture (Hope, Harrison, Mission)

Fraser Valley winters are wet. Warm, moist air from your living space rises into the attic. If it can't escape, it condenses on cold roof decking, leading to:

• Mold and mildew growth
• Wood rot
• Insulation degradation
• Interior ceiling stains

Proper Ventilation: Removes moist air before it condenses, keeping attic dry.

3. Ice Dams (Hope, Harrison)

Ice dams form when heat from the living space warms the roof deck, melting snow. Meltwater runs down to the cold eaves and refreezes, creating an ice dam. Water backs up behind the dam and leaks into the home.

Proper Ventilation: Keeps the roof deck cold (same temperature as outdoor air), preventing snow melt. No melt = no ice dams.

Signs of Poor Ventilation

Summer Indicators:

• Attic temperature exceeds outdoor temperature by 15°C+
• Second-floor rooms are uncomfortably hot
• Air conditioning runs constantly
• Shingles show premature aging (curling, granule loss)

Winter Indicators:

• Frost or condensation on attic rafters
• Mold or mildew in attic
• Ice dams at eaves
• Ceiling stains in upper rooms

Common Ventilation Mistakes

1. Blocked Soffit Vents

Insulation pushed into eaves blocks airflow from soffit vents. This is the #1 ventilation mistake we see.

Solution: Install baffles (rigid foam channels) between rafters to maintain airflow path.

2. Imbalanced System

Too much exhaust and not enough intake (or vice versa) creates inefficient airflow.

Solution: Calculate required NFA and ensure 50/50 split between intake and exhaust.

3. Mixing Ventilation Types

Combining ridge vents with gable vents can create short-circuit airflow (air enters soffit, exits gable vent, never reaches ridge).

Solution: Choose one primary exhaust system (preferably ridge vents) and stick with it.

4. No Ventilation Calculation

Many contractors install ventilation by feel, not calculation. This leads to under-ventilated attics.

Solution: Calculate attic square footage, determine required NFA, and install adequate vents.

The Bottom Line

Ventilation is invisible, but its effects are measurable: longer shingle life, lower energy costs, no ice dams, no mold. It's not optional — it's essential.

At RJ Roofing Bros, we calculate ventilation requirements for every project. We don't guess. We don't use "standard" vent spacing. We do the math.

Concerned about your attic ventilation? Call (604) 997-1292 for a free attic inspection.