Roof Vents Explained – What Are They and Why Do You Need Them

What Are Roof Vents

Roof vents are essential components of a complete roofing system. They allow your roof and attic to “breathe,” balancing air temperature and moisture levels inside your home.

In every properly built roof, there are two key types of vents—intake vents and exhaust vents—that work together to move air in and out.

Intake vents are usually installed in perforated soffits along the eaves, where they draw in cooler outside air.

Exhaust vents, such as ridge vents or box vents, sit near the roof’s peak, allowing hot or moist air to escape.

This exchange of air is what keeps your attic dry, stable, and efficient. Without vents, the attic would trap humidity and heat, eventually causing damage to the roof deck and insulation. There are also several venting styles available, including ridge vents, gable vents, and turbine vents, but not all should be used together.

Combining different systems can interrupt airflow or even pull snow and moisture into the attic. A balanced system—designed for your roof’s slope, layout, and insulation—is the foundation of a healthy, long-lasting roof.

What Do Roof Vents Do

Roof vents perform one critical function: they regulate the air circulating through your attic. When the system is balanced, air flows from the lowest point (intake) to the highest (exhaust), creating a cross-breeze effect. This movement equalizes the attic’s temperature with the outside air. For example, if it’s –10°C outdoors, the attic should also stay around –10°C. That even temperature prevents snow from melting and refreezing on your roof—a process that leads to ice dams.

During the summer, ventilation works the opposite way. Rising heat inside the attic escapes through exhaust vents, lowering overall roof temperature and easing the strain on your home’s air conditioning. If hot air can’t escape, attic temperatures can soar above 60°C, which weakens the roof sheathing, dries out shingles, and reduces their life expectancy.

Effective ventilation does more than protect the roof surface—it supports your home’s comfort and safety.

• It prevents frost and condensation from forming on attic surfaces.
• It reduces the risk of mold and mildew, which thrive in damp, enclosed spaces.
• It keeps insulation dry, helping it perform as intended.
• It prevents heat buildup that can cause wood to warp or delaminate.

A well-vented roof protects what you can’t see—the structure beneath the shingles.

Why Do You Need Roof Vents

You need roof vents because they are your roof’s defense against moisture, temperature swings, and structural decay. Without ventilation, the attic becomes a closed environment where warm indoor air and cold exterior air collide. This meeting point creates condensation—tiny droplets that settle on beams, nails, and insulation. Over time, these droplets cause wood rot, mold growth, and ceiling damage.

In winter, poor ventilation is one of the leading causes of ice damming. When attic air is too warm, snow on the roof melts during the day, runs down the slope, and refreezes along the eaves. These frozen ridges trap water behind them, pushing moisture up under shingles and into the roof deck. Inside, you might notice water stains or soft spots in drywall—both signs of a ventilation issue rather than a leak in the shingles.

In summer, the effects are different but just as damaging. Trapped heat bakes the roof from the inside out, breaking down adhesives, drying wood, and warping chipboard sheathing. High attic temperatures also force your cooling system to work harder, increasing energy costs. Over time, heat and moisture will shorten your roof’s lifespan and compromise its structure.

Proper ventilation is both preventive and protective. It keeps the attic cool in summer, cold in winter, and dry all year long. When paired with the right insulation, it forms a complete system that maintains your home’s comfort while preserving the roof’s integrity.

Roof Vent Regulations in Ontario

Ontario’s building code sets specific standards for how much ventilation a roof must have. These regulations have tightened over time as building science has improved. Today, balanced ventilation—meaning equal intake and exhaust—is required by code. Every roof must allow a certain amount of airflow for each square foot of attic space to prevent moisture buildup and ensure energy efficiency.

When a home is re-roofed, its ventilation system must be updated to meet current codes. Installing new shingles on an old, under-vented roof can invalidate your manufacturer’s warranty. Most shingle producers will only honour their warranty if the attic ventilation meets the proper ratio of vent area to roof size. A roof that overheats or traps condensation may show premature shingle wear, curling, or discoloration—all signs that can disqualify a warranty claim.

Homeowners should also be cautious about layering new shingles over old ones. A second layer adds weight and blocks airflow from reaching the attic, which can further trap heat and moisture. Ontario building codes and most roofing manufacturers recommend full removal before re-roofing so that ventilation and underlayments can be correctly inspected and replaced.

These requirements aren’t only about compliance—they ensure that your roof performs safely and efficiently in Ontario’s demanding climate.

Building Requirements and Bylaws Have Changed Over Time

Roof vent standards have evolved as builders and inspectors have learned more about how homes interact with temperature and humidity. Decades ago, many believed black shingles caused excessive attic heat, when in fact, poor ventilation was the real issue. Attics in older homes often had little to no airflow, which led to ice dams, heat buildup, and structural decay.

Modern roofing practices are based on scientific understanding of airflow, insulation, and moisture control. Building codes now require more ventilation openings, better soffit design, and improved insulation. These updates help manage heat loss in winter and heat gain in summer, keeping your attic temperature stable.

When you replace or repair your roof, it’s important to confirm that your contractor checks both ventilation and insulation. Many older homes in Ontario still rely on outdated systems or blocked soffits. A professional roofer can evaluate whether your attic has enough intake vents, ridge vents, or upgraded soffits to meet current standards.

Keeping your home up to date with modern requirements has clear benefits:

• Your shingles last longer because heat and moisture are controlled.
• Your attic stays dry, protecting insulation and wood framing.
• Your roof remains compliant with both building codes and warranty conditions.

These improvements are not cosmetic—they’re essential to protecting your investment. When your roof breathes as it should, your entire home benefits.

Chouinard Bros Specializes in Roof Repair and Maintenance

Your roof protects everything beneath it — and proper ventilation keeps that protection strong. If you’re unsure about your attic airflow or think your vents might not meet today’s standards, it’s the right time to have a professional take a look.

Chouinard Bros has decades of experience diagnosing ventilation issues, repairing roof systems, and keeping Ontario homes safe and efficient through every season.

Our experts can inspect your roof, recommend practical solutions, and make sure your home meets current code and warranty requirements.

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