Uniform Building Code (UBC)
Strange as it seems, the code listed below applies to all homes, regardless of where they are constructed. Homes built in -20F have the same code as those built in a desert environment?
Section 1505 subsection 1503 of the UBC,
states as follows:
"Ventilation, where determined necessary by the building official due to atmospheric or climate conditions, enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the rain and snow. The net free ventilation area shall not be less than 1/150 of the area of the space ventilated."
EXCEPTIONS: 1. the area may be 1/300 of the area of the space ventilated
provided 50 percent of the required ventilating area is provided by ventilators
located in the upper portion of the space to be ventilated at least 3 feet
(914mm) above eaves or cornice vents with the balance of the required
ventilation provided by eaves or cornice vents.
2. The area may be 1/300 of the area of the space ventilated provided a vapor barrier having a transmission rate not exceeding 1 perm is installed on the warm side of the attic insulation.
Translated? 1 divided by 150 x 1000 square feet of attic equates to 6.6 square feet of venting per 1000 square feet of attic. Place half of your vents at the eaves and half at the peak and you can get away with 3.3 square feet of venting. Keep in mind this is the minimum requirement to meet code.
Years of testing in hot
and cold climates and before and after applications of various venting size and
locations prove the following: the UBC code falls short in it's goal of
providing accurate information for adequate venting.
The suggestions on our venting page are the culmination of years of field testing on what does and does not work in both desert and cold climates. This will help you even you if you are not using a radiant barrier in your attic and absolutely necessary if you are.
Click here to return to our venting page