Irc Attic Ventilation Requirements

For large volume attics such as where roof slopes.

Irc attic ventilation requirements. Vented attics shall have a minimum net free ventilation area at least 1 300 of the area of the vented space. 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. Nrca guidelines regarding attic ventilation nrca recommends designers provide at least 1 square foot of nfva for every 150 square feet of attic space 1 150 ventilation ratio measured at the attic floor level ceiling. More ventilation at the soffitsthan at the ridge will allow the attic to be slightly pressurized irc 2012 requirements reflect this approach for best results provide 50 to 75 of ventilation space at the soffits 60 40 is the optimal split.

The amount of ventilation can be reduced to 1 300 in effect 50 less but 2 conditions must be met effective 1 1 18. The international code council icc is a non profit organization dedicated to developing model codes and standards used in the design build and compliance process. The ventilation amount and opening size requirements can be found in section 806 roof ventilation of chapter 8 roof ceiling construction. Pdf 2015 international residential code for attic ventilation 145 kb.

The minimum net area of ventilation openings shall be not less than 1 square foot for each 150 square feet of under floor space area unless the ground surface is covered by class 1 vapor retarder material. The following are the requirements taken directly from the irc. Also when using a vapor retarder in an attic space irc 2012 limits the net free ventilation reduction from 1 150 to 1 300 for buildings in climate zones 6 7 and 8. The ventilation openings shall have a least dimension of 1 16 inch 1 6 mm minimum and 1 4 inch 6 4 mm maximum.

Attic floor is defined as length x width floor of the attic. Between half and two thirds of the provided ventilation shall be installed at the eaves.