Why is Roof Ventilation So Important?

House photo after roof replacement and proper ventilation

The typical home is built with a wood frame and the roof is a steep slope, covered by asphalt shingles, though a minority of homeowners will choose cedar or other materials. The rafter and attic spaces are typically closed off, which means they could be prone to moisture problems. One of the most common ways to fight moisture buildup is to provide proper ventilation.

The moisture factor

In an improperly vented roof, moisture is allowed to rise up and condense in the attic. This will damage insulation and studs and any other material that has prolonged contact with the moisture. Furthermore, dangerous mold and mildew can grow. Finally, moisture will also cause rot.

Proper ventilation isn’t solely about moisture buildup in the attic and rafter area, it also has implications for the exterior. For example, an unvented roof will allow heat to enter the attic during the winter. If there is any snow on top of the roof, the heat will melt it, causing a destructive ice dam to accumulate.

During the summer, an unvented roof will cause a severe heat buildup. For example, on a 90 degree day, which is typical for a Midwestern summer day, the heat in the attic or rafters can get up to 140 degrees. Combine this with moisture and you’ll find your roof decking and shingles becoming distorted. This can result in cracks that allow moisture to seep in from the outside.

How proper venting works

Air must be allowed to move freely in your attic throughout the year. However, there must a pattern to the airflow and there are different factors that influence how air moves around.

When built correctly, roofs do not require a powered ventilation system. For example, with the proper setup, cold and warm air will move in something called the stack effect. As the warm air rises, it cause the pressure to go up at the top of the attic, forcing air out of the upper vents. This flow forces air to enter at the lower vents, creating an excellent flow.

The wind can also have an effect on how air moves through an attic. As the wind flows over the exterior surface of the roof, a high and low air pressure system is created. The low pressure sends air into the attic while the high pressure moves it out.

Myths about ventilation

Perhaps you’ve heard that only houses in warm climates require ventilation? Well, our tip about snowmelt should debunk that myth.

Or, maybe you’ve heard that during the cold winter months, ventilation sucks the warm air out of your house? This is only true if your home is poorly insulated. You might be surprised to find that on a cold but sunny day, your attic might be warmer than the rest of your house, but only because the sun is warming up your roof.

If you can see vents around your roof, you might believe that you have proper ventilation. This is also a myth. For instance, you might have gable vents and think you’re covered. Unfortunately, those alone provide limited air movement.

Free roof inspection to notice any damage early

It’s difficult to know what level of ventilation you have going in your attic, which is why you need to contact a professional to inspect the situation. At VIS Exterior, we know roofs and we can inspect residential and commercial structures for proper ventilation. Contact us today and we’ll get to the bottom of your roofing needs.