All About Roof Ventilation
Roof ventilation is a very important issue that homeowners don’t think of often. In the summer, the sun heats the air in the attic. In the winter, heat from your home warms the attic. In either season, good venting occurs when cold air can enter the attic near the eaves and exit near the peak. The goal is that temperature and humidity levels in the attic space match the conditions outdoors. The best way to fight moisture buildup on a roof is to provide proper ventilation.
How Ventilation Works
Ventilation works on the principle that heated air naturally rises. It uses two types of vents:
- Intake vents – These are at the lowest part of the roof, under the eaves. They allow cool air to enter the attic.
- Hot air exhaust vents – These are at the peak of the roof. They allow hot air to escape.
The general rule of thumb for ventilation suggests installing at least 1 square foot for every 300 square foot of attic floor. Building codes vary, so be sure to check for the specifics for your home.
Most commonly installed directly in the soffit, this type of vent is installed either as individual vents spaced every few feet or as one continuous perforated soffit running the entire length of the eave. The problem posed by this type of vent is their positioning. Homeowners can accidentally block them when insulating the attic. Blocked soffit vents are just as bad as no vents, because they prevent fresh air from freely flowing into the attic.
Homes with gable style roofs may also have vents on the side of the house as high as possible within the peak of the gable. They’re valuable for their ability to act as both intake and exhaust vents, depending on the direction of the wind.
You can release the heat that rises and gets trapped in the attic with one or a combination of the following vent models:
This type of vent is openings that run the entire length of your roof along the ridge. They are a popular type of ventilation because they create no disruption to the roofline. The homeowner can be hidden or camouflaged easily. Because of this, they’re often only visible to a trained eye. Installing this type of attic ventilation involves leaving a gap in the sheathing along the ride and covering it with a perforated vent.
Static vents often protrude from the roofline thanks to special covers to keep precipitation from entering the attic. Manufacturers design this type of vent in a variety of shapes and colors so they can closely match the homeowners’ shingles. Whatever type of static vent, it must be located as close to the ridge as possible.
Powered Exhaust Vents
Powered exhaust vents feature an electric or solar powered fan to create an effect similar to that of a turbine. This type of vent turns on when the temperature inside the attic reaches a limit and runs until the temperature drops. They will pull more cool air from any air leaks in the ceiling of your house than a soffit vent because it’s easier. Additional energy spent on air conditioning cooling the entire house may make this type of vent less desirable. Poor insulation exacerbates this problem.
Dangers Of Bad Ventilation
In an improperly vented roof, moisture may rise and condense in the attic. Since most ceilings are not perfectly sealed, the warm and humid air leaks into the attic. The condensation forms on the roof framing and sheathing. This moisture damages insulation and studs, as well as any other material that has prolonged contact with the moisture. Moisture can cause dangerous mold, mildew, and even rot. The water can also drip onto and through your ceiling, causing even more damage. Leaving moisture too long can cause you to have to repair or replace your entire roof.
Proper ventilation has not only implications for the interior of a home. It can also affect the interior. For example, an unvented roof allows heat to enter the attic during the winter. If there is snow on the top of the roof, the heat will melt it. This will cause a destructive ice dam to accumulate that can find its way under the shingles.
Similarly, an unvented roof causes problems in the summer, too. An unvented roof causes severe heat build up. Combine heat with moisture and you find that shingles may become distorted. This results in cracks that allow moisture to seep in from the outside.
Air must move freely in your attic throughout the year. There must be a pattern to the airflow. There are different factors that influence how air moves around.
When built correctly, roofs do not require a powered ventilation system. With the right setup, cold and warm air will move in the “stack effect.” As warm air rises, the pressure goes up at the top of the attic, forcing air out of the upper vents. This flow forces air to enter the lower vents, which creates an excellent flow.
Wind also influences how air moves through an attic. As the wind flows over the exterior surface of a roof, it creates a high and low air pressure system. The low pressure sends air into the attic while the high pressure moves it out.
Myths About Ventilation
Let’s debunk a few myths about ventilation. Have you heard that only houses in warm climates require ventilation? That is wrong. Just look to our tip about snowmelt. What about this one, did you hear that ventilation sucks out the warm air out of your house during the cold months? This is only true if your home is poorly insulated.
Seeing vents around your roof doesn’t mean that you have proper ventilation, either. It’s best to have a professional assess your ventilation system to ensure it is right for your home.
Maintenance of Your Roof Ventilation
Vents often get plugged up by debris, cobwebs, and even stray insulation. While wearing eye protection, clear them with a compressor and an air nozzle or a leaf blower.
Check your neighbors roofs after a snowstorm. If your roof is bare while the others are still snow-covered, you could be in trouble. Your roof may just be warmer because of its design or location, or it means you have poor ventilation or inadequate insulation.
A properly maintained and ventilated roof has implications for your roof maintenance, as well. Because heat degrades asphalt shingles, ventilation keeps them cooler, extending the life of the roof.
It’s important to remember that we offer free estimates for your roof. Call us at 636-699-0449 today to get started.