2021 International Residential Code for One- and Two-Family Dwellings

Every 3 years the International Residential building Code (IRC) releases code updates. 2021 is a cycle year. Below is the attic ventilation section. Key notes:


  • The minimum amount of attic ventilation remains 1/150 (1 square foot of Net Free Area for every 150 square feet of attic floor space. Attic floor is defined as length x width FLOOR of the attic).

  • The amount of ventilation can be reduced to 1/300 (in effect 50% less) BUT 2 conditions must be met (read the full code language in the PDF below).

  • Renewed for 2021 is the requirement that “Vents must be installed according to the vent manufacturer.” This includes: Don’t Mix Exhaust Types (ridge vents, wind turbines, box vents, gable louvers, power fans); and Exhaust Ventilation Must be Balanced with Intake Ventilation. (see the Installation Instructions for the ventilation product).


 pdf smallRead the full 2021 Bulletin Here



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