What Happens When a Roof Doesn’t Have Proper Ventilation?

One of the most important aspects of the way your roof is designed and built is proper ventilation. You simply cannot over-estimate its importance.  What happens when a roof doesn’t have proper ventilation?  Improper ventilation allows formation of condensation, moisture accumulation, and damage to the roof deck and, eventually, to the stability of the roof.  Improper roof ventilation can also affect the health of your family.

The industry standard for roof ventilation to provide 1 square foot of intake ventilation and 1 square foot of exhaust or outflow ventilation for every 300 square feet of attic space, provided the area is insulated with a vapor barrier.  If the area is insulated without a vapor barrier, the requirement doubles. 

Proper ventilation of the roof and attic of a home achieves several important functions:

Several types of vents can be used to properly ventilate the roof of your home.  Roof ridge vents are placed along the ridge line of the roof. Ridge vents are used for exhaust or outflow of moisture, heat, and stale air. Soffit vents and Eaves are placed at the lower extremes of the roof and provide the intake ventilation.  If you live in an older home, your roof might not be constructed for roof ridge or soffit vents. Older homes were not built with the tight seals of today’s houses. There were cracks and openings around windows and doors, chimneys and other openings.  These cracks and openings allowed fresh air to flow into the house.  On the principle that hot air rises, the accumulated heat and moisture would rise to the attic and out the roof vents.

Without adequate ventilation, moisture rises with the hot air and forms condensation on the inside of the roof deck. This moisture is released into the air inside the house from bathing, cooking, plants, laundry and other causes.  When the condensation forms on the roof deck, it begins to rot the wood.  This introduces mold spores into the air, as well as damaging the wood.  The result, if the problem is not noticed and repaired, can be destruction of all or part of the roof deck and creation of unhealthy air inside the house.

In our increasingly airtight homes, the importance of proper ventilation in roof construction cannot be over-emphasized.  It is important to take the time and do the research to understand the ventilation needs for your home in your region and how best to meet those needs.