unfinished atticNot that long ago, I discovered the reason why my house was slowly turning into a sauna. Summer or winter, it didn’t make a difference – my house was hot all the time, thanks to my poorly ventilated attic. If you’re in the market for a home, you’ll soon discover why venting your attic is important. Now that I know the ins and outs of attics, I wanted to share more about what I’ve learned about venting your attic if you don’t have eaves.

I live in a small, square house. It’s a classic post-war ranch house, built in the ‘50s to meet the needs of the soldiers returning from WW2 and the needs of their growing families. The houses were built with speed and efficiency in mind. We bought our house from the original owners who never made any updates aside from putting wood paneling OVER the drywall in every room and installing light switches that don’t attach to anything. So aside from the nostalgia factor our home provides, it has none of the modern-day architectural advancements that could make our lives a lot easier.

Most post-war ranches are one-story houses with a low roof pitch and shallow eaves with a flat soffit. Did I just lose you? I thought so. Let me break it down. A roof pitch is how steep the slope of the roof is. For example, the Addams Family house has a high roof pitch. The eaves are the part of the roof that hangs over the walls of the house. A great example of great wide eaves are the homes of Frank Lloyd Wright. He loved big eaves. Soffits are the underside of the eaves. So if you have shallow eaves with a flat soffit, you have a very small overhang that has a flat bottom.

Passive Ventilation

Now that we have that out of the way, let’s get to the heart of the matter – venting a house with little to no eaves or soffits. The most common way to add ventilation to an attic is by installing air intakes in the soffits and putting an outlet at the gable of the house. This creates a natural air flow by drawing in the air from outside, pushing it up and out through the vent at the top of the house. This is called passive ventilation.

Passive ventilation relies on the differences of air pressure from the outside and the inside of your attic. Cooler air is heavier and denser; it’s pulled into the attic from the soffit, where it warms up and becomes lighter and less dense, and then escapes through the vent in the gable. This pressure creates a vacuum, drawing in the cold air to replace the hot air that has been lost through the gable. But if you don’t have eaves or if you have shallow soffits like me, ventilation can be a challenge.

One great alternative to a soffit ventilation system is to install an intake vent right at the lower edge of the roof. They call this a venting drip edge. The venting drip edge seems to be the easiest and most common way to go. In most cases, all you have to do is remove about one inch off the top of the fascia (the part that covers the end of the rafters on the roof), install the drip edge, finish with a vent that’s on the top of the roof and you’re good to go. This is a much cheaper alternative to extending the roof line and building new soffits. The challenge with drip edge vents is that they provide less air intake and are more prone to leakage in areas where there’s a lot of ice and snow.

A shingle-over intake vent provides a larger intake area than the venting drip edge. These vents sit right at the roof edge, or sometimes mid-roof, and are placed under the shingles directly on the roof. The benefits of using shingle-over intake vents are that they provide a large amount of intake area for their size, they’re relatively easy to install and they work well in areas that get a lot of snow and ice. Additionally, they’re the most aesthetically pleasing of all the vents. They’re virtually invisible if you’re standing on the ground looking up at the house.

Sometimes a home without eaves or soffits will use ridge vents. These fixed venting units have a lot of advantages over the other venting options. One advantage is that they’re incredibly efficient. Most ridge vents use an external baffle system that’s designed to pull in cool air and push out warm air regardless of wind direction and force outside. It does this by creating an area of low pressure on both sides of the vent, which pulls the hot air right out of the attic. This is what’s known as the Bernoulli effect – the action is similar to the way the low pressure above the wings of a plane lifts it up to fly. Science!

Another advantage of ridge vents is that they create the most air moving in a uniform way. Ridge vents run the entire length of the roof and therefore help to pull air evenly throughout the entire roof. This eliminates any hot spots that can develop with exhaust vents. This is the most naturally balanced of all the fixed vent options. And finally, they look really nice because you don’t have any fixed exhaust vents sticking up from the top of your roof.

The type of exhaust vent you choose really doesn’t matter if you have no eaves or short soffits. It’s just important to remember that whatever kind of ventilation system you go with, it must be properly balanced. What that means is that the net free intake area of vents should be equal to or greater than the area of exhaust venting. So, for example, the net-free ventilation area of one shingle-over intake vent is approximately 9. The NFVA of one exhaust vent is typically about 18. You’ll then want to make sure you install two single-over intake vents to equal one exhaust vent. Additionally, half of the vent area must be high while the other half is low.

Active Ventilation

Active ventilation is what it sounds like – there’s something that creates a push/pull effect to actively draw the air in and actively push the air out. Imagine there’s a screened window on one side of your attic with a big box fan on the roof, facing outward. The cool air is sucked in by the fan and blown out of the roof by the spinning blades.

One common active ventilation system is wind turbines. These are vents that you place evenly along the gable of the home. They act as both the intake and the exhaust. They’re a great, low-cost alternative for venting, but are only maximally effective in areas where wind speeds are consistently five MPH or greater.

Another active vent system is a power fan. Unlike a wind turbine that relies on wind to power the fans, this system requires electricity. A power fan is turned on and off as needed automatically with a thermostat and humidistat control. In some cases, the thermostat and humidistat are built into the power fan. These types of ventilation systems are very powerful and can move a lot of air in a short amount of time, and they work best in areas where the air is hot and stagnant. However, they typically don’t do it uniformly and cannot vent away moisture in the winter without a humidistat control.

But keep in mind, no matter what kind of ventilation you choose or how many vents you install, it won’t matter if everything’s not insulated correctly. Gaps in the framing need to be sealed, any holes from electrical wiring must be filled, and so on. You want to keep condensation from forming anywhere in your attic. Insulate the walls carefully and effectively so that you don’t wind up with further problems down the road.

If there’s one thing I’ve learned in this journey, it’s that maintaining proper ventilation in your home is really important. Not only will it help preserve your roof, attic and overall life of your home, it’ll keep your heating and cooling bills from getting out of control, and you’ll be comfortable in your house no matter what it’s like outside! Hope this helped you!

With or without eaves, have you found a house that you love? Get started on your home loan today!

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This Post Has 9 Comments

    1. That’s a very good point, Tom! We’ll keep that in mind for future articles. Thanks for your feedback!

  1. I have a mobile home in Winnipeg and have had ceiling dripping in the past. Warming trends in January and again in April cause the roof strate to warm and evidently I had condensation ptoblrms( no soffit vents but do have small gable end vents . I reshingle this past year and pulled out old R14 insulation and retaped as many as visually possible areas of vapour barrier leaks/ cuts in material etc. With the MB insulation program I blew in insulation to fill the cavity and added two Duraflo vents to the roof area ( 52×14 ) with now 4 and a wind turbine. Last week I shivered snow from around vents and seen that the wind turbine wasn’t turning and investigated and found it was solidly iced up and took it off and noted the underside substrate as far as I could reach was ice laden.. ? The temperature is above zero now and I have numerous leaking points into the residence and discolouration of ceiling tiles. What’s next ?? Close all vents and use a ridge vent full length of residence..? Suggestions needed 🙁

  2. My roofer (well-respected, in business for many years, top marks on the rating sites, etc) said he would not recommend a shingle-over roof vent because of ice-damming issues. This article could be improved by adding some discussion of the claim that “they work well in areas that get a lot of snow and ice”.

    1. You can use a shingle over vent at the bottom or mid-roof, mid roof being higher up than the potential ice damming. Ice damming is caused by the warmer attic space melting the snow down to the cooler eaves where it freezes. properly vented attic space will not do that because its theoretically the same temp as it is outside.

  3. Very informative, I must protect the attic first….. I share my walls with condos and if water get at ground level it’s even more problems. My concern is can an attic vent flow be to large and let water in and does spray insulation keep attic protected by leak in.

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