Updates to residential roof ventilation submittal requirements

The information requested is as follows:

1. Specification on plans for the net free ventilation rate (i.e. 1/150 or 1/300)
2. Calculation on the plans showing the minimum required net free ventilation area. Examples below:

Or

3. Specification of a Class I or II vapor retarder on the warm-in-winter side of the ceiling when using a net free ventilation rate of 1/300

Requiring this information is intended to make plan review, construction, and field inspection more predictable and efficient. This intent aligns with the City of Portland’s goal to reduce the overall time it takes a customer to receive a building permit.

For reference, Section R806.2 of the 2021 Oregon Residential Specialty Code reads as follows:

R806.2 Minimum vent area.  The minimum net free ventilation area shall be 1/150 of the area of the vented space.

Exception: The minimum net free ventilation area shall be 1/300 of the vented space provided both of the following conditions are met:

1. A Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
2. Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

For more information, please contact Permitting Services at 503-823-7357 or schedule a 15-minute question appointment with a residential building code reviewer.