July 5, 2017

Photo: Building Science Corporation

The main purpose of roof ventilation is to keep the air space above the roof insulation at the same temperature as the outside air. In an unoccupied attic with the insulation on the floor, the air space between the floor and the roof requires air changes to achieve this. Local residential building codes specify appropriate roof ventilation method(s) depending upon where a home is located.

Benefits of Roof Ventilation

During the heating months, the presence of warm air in an attic can melt snow and cause ice damming. When damp air enters an attic, it can lead to condensation on surfaces inside the attic and shorten the life of building materials. When cooling a house, a hot attic can increase the load on an air conditioning system. Roof ventilation can help keep spaces adjacent to the conditioned space at regulated temperatures.

Roof and attic ventilation can also increase the durability of building materials and reduce heating and cooling costs. It is important that the roof ventilation is designed in a way that does not diminish the integrity of the insulation and matches the size of the space being ventilated. Air sealing is also key to the appropriate performance of roof ventilation. It ensures there is a barrier keeping unwanted moisture and temperature changes from entering unconditioned spaces.

Why You Should Keep Unconditioned Spaces Separated

Insulation is the thermal barrier of a home which reduces the temperature changes between the interior conditioned spaces and the exterior/outside unconditioned spaces. Air sealing is the work that closes holes between the conditioned and unconditioned spaces. If there are holes from the conditioned space that allow air into the insulation, this will affect how several systems in a building function. Roof ventilation is one of the systems that performs best when air sealing has been properly completed.

A passive roof ventilation system, which has openings low and high, is designed to move air in an unconditioned space using the natural flow of air called stack effect. Air moves naturally as it does in a chimney, entering at low points and exiting out openings at higher levels. If there are openings from the conditioned space into the ventilated, unconditioned space, then roof ventilation can pull air from the home and not function as intended. This can cause problems during both the heating and cooling seasons.

How to Know if a Roof is Properly Ventilated

There are contractors that can complete a visual and diagnostic inspection to ensure that your home’s attic is ventilated according to local codes and BPI standards. During an energy audit, the contractor will measure the ventilation openings and ensure that the path is set up to perform in a way that does not reduce the effectiveness of insulation. A blower door test will be completed to discover any air sealing improvements that can benefit a home’s durability, comfort, and whole-house performance.

Contact an experienced contractor (such as a BPI GoldStar Contractor or BPI Certified Professional) to inspect your attic to determine which technique would be most cost efficient and effective for your home.

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Jeremy O'Brien

Jeremy O'Brien joined the Building Performance Institute, Inc. team in 2009 and currently works as a Technical Relations Representative. Jeremy has worked in the home performance industry for 18 years and has had many roles such as energy auditor, air sealer, insulator and more. At BPI, his duties include completing quality assurance inspections, proctoring exams, assisting with exam and standards development and providing responses to technical questions on the BPI.org website.