Attic ventilation is one of the most published roofing topics on the internet today. There are countless articles and blogs available for homeowners from various resources. While many of these articles have similar themes, I have noticed some varying opinions on the importance and benefits of ventilation. I have also noticed that ventilation is sometimes a scapegoat for a deeper, more underlying problem. In today’s article, I want to cover what I feel are the truths about attic ventilation regarding its importance and benefits. I also want to mention where I see ventilation (specifically, the lack of) as being unfairly blamed for issues and deficiencies that have deeper rooted problems. I will also discuss some common products used for attic ventilation.
In simplest terms, attic ventilation is a process of creating air movement and circulation in the attic space. While there are different product options available, The process is typically done with a source of intake air (fresh air normally drawn from the soffit or near the eaves) and a source of exhaust (typically near or at the roof’s peak)
Ventilation is important for two (2) main reasons:
The diagram above illustrates an appropriate attic ventilation arrangement. There is fresh air coming in at the soffits (intake venting) while the warmer air is exhausting closer to the peak (exhaust venting). This arrangement accomplishes both ample air flow to help reduce or prevent condensation while providing a constant flow of fresh intake air, which will keep the attic temperature consistent with the outdoor temperature.
According to OBC (Ontario Building Code) Standards, proper attic ventilation requires two main components:
A balanced venting system – where an equal amount of air comes in at the soffit region and an equal amount of air exhausts near the roof peak. In theory, balancing the venting system is important in order to maintain appropriate air pressure in the attic space.
Too much intake and lack of exhaust can result in high pressure. In this scenario, the attic is susceptible to summertime superheating, which can make the upstairs space uncomfortable. It can also compromise some warranties with some shingle manufacturers.
Too much exhaust and a lack of intake venting can cause the attic to depressurize. The result is often air from your home will be pulled into the attic. While I have read other resources that claim ice dams and condensation can result from this, my experience has been that an increase in energy costs is likely the worse case scenario (I’ll touch on ice dam and condensation issues a little later)
Of these 2 scenarios, the first is much easier to fix. However, according to most shingle manufacturers, the second scenario is most important for peak performance from shingles. Most homes built in the last 30 years or so have adequate venting, both in a balanced sense and from a volume perspective.
An adequate amount of air flow – In addition to a balanced venting system, having a minimum amount of air flowing in and out of the attic is also important. OBC Standards and most shingle manufacturers define the adequate amount as 1 sq ft of net free venting per 300 sq ft of attic space.
There are a number of products available for venting your attic space. When it comes to choosing a venting product, I like to keep it simple and follow a few basic rules:
Referring to some of the theory on roof ventilation as mythical maybe a bit strong and will likely open the door for debate with some. I would, however, like to share my experiences regarding ventilation (particularly the lack of it) in an unbiased and hopefully beneficial way.
Poor ventilation does not cause ice dams. At best, venting can mitigate this issue, but it cannot solve ice dam issues on its own. Ice dams occur when the attic temperature is above freezing while the roof temperature is below freezing. The warmer attic air will melt the ice and snow on the roof by warming the underside of the deck. The melted ice and snow then run to the cooler soffit overhang, where it re-freezes. If the conditions are right (right mix of snow and temperature) the ice will accumulate at the eaves to a point where it creates a level plane to the roof. Water is then directed back towards the shingles, where it can cause leaks. The theory with venting is that warmer air will exhaust and be replenished with cooler air before it can melt the snow. The reality is venting is not the root of the problem. The root of the problem is warm air entering the attic. This is best prevented with attic insulation. If you have issues with ice dams on a regular basis, an insulation top up should be your priority. Ensuring you have both adequate insulation and ventilation is your best defence against ice dams.
Better Ventilation will fix my mouldy attic. For many of the same reasons, improving attic ventilation will not fix mould or condensation in the attic either. The root of the problem is warm/moist air entering the attic space and mixing with cold air. Hot air meeting cold air creates condensation. The first step in fixing this should be to improve insulation levels and fix any air leaks into the attic. Once the source of warm moist air has been stopped, the condensation issues usually go away.
My roof failed before the full warranty term. It must be a ventilation problem. I will tread lightly here, as adequate ventilation is an important part of most shingle warranties. While providing estimates for customers, I often hear the disappointment that their so called 25 year shingle failed in 12-15 years. Homeowners who start to do some research may conclude poor ventilation was the culprit. This is very seldom the case. The reason is usually more to do with the quality of asphalt and stabilizers that were used in the asphalt. Beyond that, UV exposure also plays a big role. That’s why you will notice the West and South sides wearing quicker than the North and East sides (More UV ray exposure in the West and Southern skies.)
In closing, attic ventilation is an important part of the entire roof system. Following best practices as set by shingle manufacturers and OBC Standards should be a priority for all roofing contractors. With this in mind, I find simple, proven venting systems work the best over the long term. I also think it’s important to note that ventilation, while important, is not the answer for larger, more underlying issues such as ice dams or condensation. Fixing these issues usually requires a little more digging.
For more information on venting, roofing or insulation, contact Logik Roofing today.