Irc Attic Ventilation Requirements

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.

Irc attic ventilation requirements.

The international codes i codes are the widely accepted comprehensive set of model codes used in the us and abroad to help ensure the engineering of safe sustainable affordable and resilient structures. The ventilation amount and opening size requirements can be found in section 806 roof ventilation of chapter 8 roof ceiling construction. Vented attics shall have a minimum net free ventilation area at least 1 300 of the area of the vented space. Attic floor is defined as length x width floor of the attic.

The majority of the requirements related to attic ventilation have not changed much from the previous editions. Between half and two thirds of the provided ventilation shall be installed at the eaves. 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 amount of ventilation can be reduced to 1 300 in effect 50 less but 2 conditions must be met effective 1 1 18.

For large volume attics such as where roof slopes. 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. 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 following are the requirements taken directly from the irc.

2015 international residential code for attic ventilation the code minimum ratio is 1 150. Pdf 2015 international residential code for attic ventilation 145 kb.