Proper Ventilation for a Healthy Roof

roof ventilation

Much like those that live under it, a roof needs to breathe. Proper ventilation helps keep moisture at bay, preventing mildew and structural damage. That said, a roof doesn’t usually rely on mechanical or electrical ventilation systems; instead, it creates natural air flow using the temperature differences in the attic. There’s a lot to learn about roofing, so let’s start by going over how roof ventilation works and signs that yours might need a professional.

How does roof ventilation work?

In roof ventilation, air comes in through the soffit (at least, usually) and goes out through an evacuation valve. There are two methods to create airflow in your roof: active and passive. The latter is the most common. In passive ventilation, the soffit and the wind outdoors work together, relying on convection to circulate air naturally.

All roofs have some type of ventilation system. When both the ventilation and insulation are properly installed, they work together to prevent ice damming, moisture damage, and even increased utility bills.

snow on shingles

The benefits of good roof ventilation

Good roof ventilation not only protects your home from mildew and mould, but it also helps cut down on heating and cooling bills. Let’s go over a few reasons to invest in your roof.

Roofing materials will last longer

Poor roof ventilation also wreaks havoc on your roof’s exterior. For example, in the winter, a hot attic, combined with the heat of the sun, can melt the snow and ice on your roof. This trickles down and then later refreezes on your roof’s edges and gutters. This forms an ice dam, and it can slowly build up underneath your roofing materials and cause damage to your roof, your attic, and the inside of your home’s walls.

How can you tell you have good ventilation? Well, for one, you won’t find ice on your roof unless the weather called for freezing rain. And, of course, good roof ventilation will save you from an early roof renovation.

icicles on a roof

Mould, water damage, and structural damage prevention

Even the best-built homes sometimes get some humidity in the attic. But when your ventilation isn’t up to par, it causes condensation to build up on the trusses and the underside of the roof. This is especially problematic in winter: the condensation freezes upon contact, forming ice, which then melts in the spring. Over time, the water drips down into the walls and onto the flooring, causing mould, mildew, and rot to develop. At that point, you’ll need a decontamination contractor.

Reduced energy costs

Attics lack climate control, so they tend to get a lot hotter than the rest of your home. And since heat rises, it can be especially bad in the summer. A well-ventilated roof will mimic the temperature outdoors in the summer, leading to decreased cooling costs. It’ll also save your roofing materials from an early death. Poor ventilation can cause your roof’s temperature to double, not only damaging your roofing materials but also causing them to deteriorate up to two times faster.

Checking your roof ventilation

Aside from your biannual roof inspection, you should also regularly check up on your roof’s ventilation. Here are a few signs that you may need a roofing contractor to take a closer look.


  • Ice dams
  • Roof damage (e.g., sagging, warping, rot, rust)


  • Water bubbles on the walls or ceiling
  • Overheating and/or high hydro bills during the summer

Inside the attic

Try to check your attic after a few cold winter nights: it’ll give you a better idea of the humidity levels. Be sure to check the vents that pass through the ceiling, plumbing columns, chimney flues, and entrances to recessed wires and lights. Signs of moisture tend to show up in these locations.

  • Ice buildup, especially under the gables
  • Mould
  • Flaking rot
  • Dark circles on wood and insulation
  • Rusty nails
  • Strong and abnormal odours
  • Blackened wood

My roof has poor ventilation. What should I do?

We recommend reaching out to a professional roofer to evaluate the situation. In some cases, you may not need to redo your entire roof to fix the problem.

Add roof vents

If you have minor ventilation problems in specific parts of your roof, like the gables, a roofer can add air vents in those areas. That said, because of their low profile, they can get blocked by snow during the winter. Some professionals recommend using larger vents like those sold by Ventilation Maximum to avoid this problem.

roof ventilator

Unclog or replace your soffits

If you notice that your attic is abnormally humid or warm, take a moment to inspect your soffits. They can become blocked or clogged by a variety of things, from shifting insulation materials to bird nests. In some cases, you just need to clean your soffits to solve the problem. If your soffits aren’t ventilated, you may want to consider replacing them with a better model – one with holes that allows air to circulate properly.

Replace your insulation

If you’re having trouble keeping the heat in your home, it might be the insulation that’s causing problems. For example, you might realize that your attic is uninsulated or unevenly insulated. Whether caused by contractor oversight, decay from old age, or pests taking up residence in your home, these uninsulated areas allow heat to escape. Condensation might build up in those spots as well, which can lead to mould over time. In this case, reinsulating your attic will fix your air circulation problems. And not only will you keep the heat inside your home, but you’ll also save on your heating bill while extending your roof’s lifespan.


Avoid truss issues with regular inspections

Much like the rest of your home, your roof and attic need a little love and care to function properly. Take some time each year to inspect your roof, check for building envelope problems, and prepare your home for the winter. It’ll help maintain your roof, keep your home comfortable in all seasons, and curb replacement costs.