Attic Air Ventilation

There are very few things that are as important to the long-term performance of your home’s roof as the ventilation and the attic space that lies directly beneath the roof. Have you ever wondered why your attic smells so incredibly musty? In many instances, the lack of adequate ventilation can result in the musty odor that you smell in addition to voiding the manufacturer’s warranty of your asphalt shingle if there is any damage to your roof that is a direct result of inadequate ventilation.

Do You Have Adequate Ventilation?

Ventilation is able to be accomplished via multiple techniques and products. Prior to us getting into how an attic space can be ventilated, it is important that you first understand the amount of ventilation that is necessary. Ventilation of attic areas is required by roofing material manufacturers, most building codes, as well as the National Roofing Contractors Association. When it comes to building codes, there is generally a ratio of 1/150 ventilation to attic floor space that is required. You can talk to your local municipality about the specifics of your local building codes.

To get a better understanding, here is an example. Mr. Smith has an attic space that measures 22 feet by 48 feet, which equals 1,056 square feet. He takes the square footage measurement and divides it by 150, which equals 7.04 square feet of required ventilation space. Mr. Smith now needs to take this amount of require ventilation space and compare it to the total ventilation that he currently has for his attic.

Venting the Attic

There are several options available when it comes to providing sufficient ventilation for your attic. As with any assortment of products, there isn’t a single solution that is a fix-all for any and all situations. Therefore, it is important to compare all options available to you before selecting a final solution for installation. Here is a list of installation options that you have available.

  • Ridge Vent – This is a ventilation strip that you place along the ridge line of your home. Before installing it, a piece of the roof decking—a one-inch wide strip—is cut along each side of the ride line so that there is space for air to move through the vent. This is an important step to ensure that airflow is not impeded.
  • Soffit Vents – An integral part of installing a ventilation system in your roofing system is to ensure that there is an entry and exit point for airflow. It’s important that you review the soffit areas for soffit vents, as these permit convective movement of air from the soffits to the ridge vent. Also, insulation baffles need to be installed where the floor of the attic meets the roof line to avoid the insulation in the attic migrating into the cavities and potentially restricting airflow from the vents.
  • Powered Attic Fans/Whole House Fans – Vents and fans can be installed to draw air out of the attic and send it outside. They can be controlled by a thermostat or switch that detects the build-up of heat in the attic and automatically exhausts the attic space. You may want to consider a solar-powered option, depending on the fan’s location.
  • Gable Vents – These are vents that are placed in the gable ends of the building and are typically louvered vents that permit air to be drawn out of the space while also preventing moisture from snow, rain, etc. from blowing back inside.
  • Additional Options – There are many other options available for installation depending on the home’s construction. For instance, mushroom vents, louvered dormers, and others can permit certain areas of the attic to be properly ventilated.

Calculating Requirements of Attic Ventilation

Let’s go back to the example we used earlier with Mr. Smith. The calculation shows that he requires 8 square feet of attic ventilation space. The next step is to determine the total amount of ventilation that he currently has in his attic. His home is 48 feet long with a ridge vent that measures 46 feet. This ridge vent is cut back an inch on both sides of the roof’s ridge lines, yielding a total area of 7.67 square feet of ventilation. Mr. Smith has sufficient ventilation along the ridge for the attic space to be ventilated.

Now, Mr. Smith must take a look at the ventilation through the soffit areas to create cross ventilation that is required for maximum efficiency for the ridge vent. During his examination, he determines that he has solid wood soffits that don’t offer any ventilation. For that reason, he needs to install soffit vents. Also, he needs to assess the insulation where the attic floor and roof rafters meet to make sure there is sufficient airflow and the soffit vents aren’t obstructed in any way.

In Conclusion

Ventilation is more important than many homeowners realize to multiple aspects of the home. For example, the life expectancy of your roof, the comfort of the home, as well as the performance of your HVAC systems can all be impacted by inadequate ventilation. For more information, give us a call at C and K Roofing.

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