Attic Ventilation 1 300 Rule

Based on your 1100 sq.

Attic ventilation 1 300 rule. 1 500 square feet 300 5 square feet. Near ridge of the roof. Of vent for every 300 sq. 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.

So in our example we will divide the 1 500 square feet by 300. In climate zones 6 7 and 8 a class i or ii vapor retarder is installed on the warm in winter side of the ceiling. And this guideline you ll need a minimum of. Most codes use the 1 300 rule for minimum residential attic ventilation recommendations.

1 300 or 1 150 has to do with weather there is soffit venting or not. Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge. Space irc 2012 limits the net free ventilation reduction from 1 150 to 1 300 for buildings in climate zones 6 7 and 8. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space.

In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. No soffits means 1sq ft 144 sq inches of venting for every 150 sq ft of attic space if soffit venting is there 1sq ft 144 sq inches venting per 300 sq ft. No attic vents should be installed between the intake and exhaust vents. Ok so now we know the square footage of the attic area to be ventilated.

Now let s figure out how much ventilation space we need. This means that for every 300 square feet of enclosed attic space 1 square foot of ventilation is required with half at the upper portion exhaust vents and half in the lower portion intake vents. The minimum net free ventilation area shall be 1 300 of the vented space provided both of the following conditions are met. When you purchase vents check the square inches for those vents they range from 38 49 or as high as 100 inches per vent so do the math.

The 1 300 rule 1 square foot of attic ventilation net free vent area per 300 square feet of attic floor space. In the gba article lstiburek s rules for venting roofs 07 24 2011 he notes the importance of having continuous soffit vent so the entire under side of the roof gets air flow. Remember the minimum area requirement when using a continuous system is a ratio of 1 300.