Attic Ventilation: Preventing Condensation One Vent At A Time

When it comes to condensation prevention, there is no greater factor to consider than proper attic ventilation. Most homeowners are probably aware that the majority of roofs are vented. What they may not know, or fully understand, is that many homes do not have enough attic ventilation. This lack of adequate air intake and/or exhaust can increase the cost of your energy bills. It can also cause condensation build-up and interior water damage.

Why Is Attic Ventilation Important?

Without proper attic ventilation, hot and humid air is not able to leave the space, it is instead forced to sit stagnant. During the winter months especially, this humid air will hit the much colder roof deck before condensing. Frost is often the result. Frost caused by condensation build-up eventually has to melt, and when it does your attic insulation is going to act like a large sponge. When that sponge gets too full, or when that water finds a gap in the vapour barrier, condensation leaks are the result.

Frost is present on the nails
Frost is visible on the nails, and on the underside of the roof deck. This is caused by condensation in the attic space, as a result of inadequate attic ventilation.

Interior water damage caused by condensation occurs frequently throughout the winter months, as too many homeowners just simply do not understand the sheer importance of attic ventilation. A delicate balance of intake and exhaust ventilation is needed to keep our attic spaces, and roofing systems in good health.

The Importance of Air Intake

Most homes will have soffit panels installed around their perimeter. Best case scenario, these soffit panels will be vented and allow cool air to be pulled into the attic space. Unfortunately, time and time again we see homes with minimal soffit vents, or none installed at all. Even when vented soffit panels are present on a home, there is no way of knowing from a purely external examination, whether or not they are blocked by wood or insulation. Which is why regular attic inspections are recommended.

When soffit panels become blocked within the attic space, often by insulation, it prevents the exhaust vents from pulling cool air into the space. When no cool air is able to enter the space, humidity is able to build and this is when condensation issues form.

The soffits are blocked by insulation.

What Are Attic Baffles?

Any regular home, with functional vented soffits should have an appropriate amount of baffles installed within the attic space. Attic baffles are designed to keep the insulation away from the soffit vents and maintain the flow of air into the attic.

Attic Baffles
There are no attic baffles installed at the soffits. This is disrupting the entire ventilation system.

For homes that were not designed for proper intake from the soffits, there are numerous products on the market that have shown to be just as useful in allowing cool air to be pulled into the attic. These include: edge venting, and V-Max intake vents. They are two of the most common types of alternative intake vents.

Edge venting
This roof has edge venting installed. This is because there is no air intake from the soffits.

Inadequate air intake upsets the delicate balance of intake and exhaust and can cause problems for the entire roofing system by allowing warm air that is full of moisture to build up instead of flushing it out with cooler, dryer air. This can also cause the shingles to deteriorate prematurely.

Exhaust Ventilation

Exhaust ventilation is equally as important as air intake, as the exhaust vents help to pull the cooler air from the soffits. However, there are many different scenarios that can disrupt the flow of air through the attic space. Because roof ventilation is a complicated science, many installers are simply under-educated in proper installation techniques. Unfortunately, this lack of knowledge can wreak havoc on the conditions within your attic space. Which can lead to serious and costly interior and exterior damage.

Some of the most common improper installation techniques are:Cross ventilation

Cross Ventilation

  • When exhaust vents are installed on opposing sides of the ridge, it can render the entire ventilation system ineffective.  With this set up, the exhaust vents will pulling air from each other, instead of the intake vents down at the soffits. This reduces the amount of hot air and moisture being pulled from the attic space and increases the chance of mould growth and wood rot.
Cross ventilation
The home is cross vented.

Mixed Ventilation

  • A mixture of different types of vents (power vents, turbine vents, box vents, solar vents) actually prevents proper ventilation because exhaust vents are not made equal. This means that the stronger exhaust vent ends up pulling air from the weaker exhaust vent(s) instead of from the intake vents resulting in a short-circuit of the system. This can also result in the premature deterioration of the shingles and can lead to moisture build up and mould growth in the attic.

Low Vents

  • Often times, installers will place an exhaust vent too low from the ridge of the roof. Because heat gets trapped at the highest part of the roof, if the exhaust vents are too low from the ridge (3-4 feet down) they end up becoming intake vents which will result in a shortage of exhaust upsetting the delicate balance of intake and exhaust and causing problems for the entire roofing system. During the winter months, vents that are too low can allow precipitation to enter and collect in the attic space. The exhaust vents can also pull in dust and dirt as well as leak as they are exposed to increased amounts of water from higher points on the roof that they have not been designed to handle.
Crossed, mixed and low vents.
The exhaust vents were installed improperly. Some are installed too low from the ridge, and there is mixed ventilation with the power vent and box vents. The home is also cross ventilated.

Bathroom & Kitchen Ventilation

More often than not, we see regular exhaust vents being used to exhaust hot and humid air from the bathroom or kitchen. This is improper and can also lead to condensation issues. When you use the wrong type of vent in this situation it can allow moisture to spill back into the attic instead of removing it.

A regular exhaust vent was used as a bathroom vent. This is allowing condensation to spill from the vent, causing ice to form around it.

It is also important to ensure that the fan hoses for either type of vent, kitchen or bathroom, be properly insulated. When these hoses are without proper insulation, it will allow the heat created from within the hose to seep into the attic space, further contributing to the condensation issues.

Bathroom Fan Hose
The bathroom fan hose is not connected to a vent. The surrounding roof deck is also wet and frosty.

Contact a Professional

It is important to remember that our attic spaces should be kept about the same temperature as the air outside. When vapour barrier or attic insulation is missing from the equation, this isn’t possible. This is because heat loss from the living space below will find its way inside of the attic. Proper attic ventilation may be even more important, as there are many factors to be considered when assessing the capabilities of your ventilation system. The best way to stave of the effects of condensation and condensation leaks is to ensure the correct balance of attic insulation and attic ventilation within your attic space. Contact a reputable and professional roofing contractor as soon as possible, if you believe that condensation is an issue within your home.