Unvented Crawl Spaces May Require an Exhaust Fan! Along with a continuous Class 1 vapor retarder an unvented crawl space might require a continuously operated mechanical exhaust ventilation system.
Section R408.3 of the International Residential Code gives three options when the crawl space is unvented. One of the options is covered in Section R403.3.2.1 which states " Continuously operated mechanical exhaust ventilation at a rate equal to 1 cubic foot per minute (0.47 ⁄) for each 50 square feet (4.7m2) of crawlspace floor area, including an air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated in accordance with Section N1103.2.1 of this code"
If you want to learn more about unvented crawl spaces or the International Residential Code requirements for unvented crawl spaces please visit our website, or click here and read the complete International Residential Code Section R408 Under-Floor Space.