Roof ventilation is key to protecting your roof and attic space. Attics and roofs need to breathe or they’ll start to decay. Remember, we produce a lot of moisture in our homes, from showering, doing laundry, cooking, doing dishes—even breathing. All of these things lead to moisture in your home, and that moisture needs to escape or you’ll run into issues like mould and rot.  

We know hot air rises and it can hold moisture. As the hot air in your home rises holding that moisture, where do you think it will end up? In your attic, and once it’s up there you’ll get condensation.

You don’t want condensation in your attic. It will soak your insulation, making it lose its R-value (a material’s resistance to heat loss or heat transfer). During winter it can lead to frost built-up on the underside of your roof, which can cause issues like mould on your roof’s sheathing, rafters, or trusses. Sometimes homeowners will think they have a leak—they’ll see a big stain on the ceiling—but really it’s just too much condensation in the attic.  

Your attic is a cold zone—or at least it should be. That means it needs to be properly sealed off from the rest of the living space below with vapour barrier and insulation and have a minimum R-value of R50. The vapour barrier must also be properly sealed with Tuck tape or acoustical caulking to help stop warm air and moisture from getting in.

Your attic must also be ventilated. That means having enough roof vents. How many depends on the size of your attic. The standard is one square foot of venting for every 150 sq. ft. but it all depends on where you live, or if there’s a vapour retarder on the ceiling of the room below the attic.

Insufficient ventilation can wear down your roof prematurely (e.g., shingles can blister due to too much heat in the attic). That means re-roofing more frequently. So it saves you money to make sure you have enough ventilation.

There are different types of roof vents. For example, there are box-style vents, which are your typical roof vent, square-shape with the open side facing the ground; soffit vents are the narrow horizontal section on the underside of your roof eaves. They’re perforated, usually made out of vinyl or aluminum.

There are also gable vents, which are located not on the roof but at the top of the wall on either end of a peaked roof. They tend to let in less moisture but they cannot work without wind. And then there are ridge vents, which run along the peak of a roof to allow for continuous airflow. I love ridge vents but they’re more labour intensive to install and more expensive.

Whether your roof has soffit or gable venting or ridge vents, the most important thing is that there are enough vents to ensure the attic is properly vented—and they cannot be blocked by insulation on the inside or snow on the outside.

I heard of one case where the roof vents on the north side of a home were constantly covered by snow. (The north side of a home tends to get more snow accumulation.) This blocked the ventilation in the attic, which led to condensation. The homeowner thought they had a leak but it was just a roof venting issue. The solution? Raising all the roof vents on the north side of the home.

Also, when adding extra insulation in your attic, which is a great idea especially before winter, make sure it doesn’t block your soffits. One solution is using Styrofoam baffles that direct airflow from the soffit to the top of the attic. Another thing I’m always finding is old wooden soffits that have been covered over with aluminum during an update or renovation, but no holes were made in the original wood soffit under the new layer of aluminum, which means there’s no venting.

We also need to make sure our roof vents are properly protected against critters. Squirrels love to chew through them and pull up the flashing that protects the roof area around the vent.

If you’re not sure if your roof has enough ventilation, contact a professional roofer and ask them to come by and take a look. It’s not a bad idea to get it checked especially as we move into winter, and usually the best roofers get booked up fast. If you invest in your roof it pays you back.