® Winter 2014 FEATURE... 7 Attic Ventilation Calculations Made EASY ALSO IN THIS ISSUE... 13 You’re Getting Sued! 19 Is the Inspector Claiming the Sky is Falling? 22 If Everyone Else Jumps...
Attic Ventilation Calculations Made EASY By: Paul Scelsi, Air Vent, Inc., on behalf of the Roof Assembly Ventilation Coalition Whether you’re a builder breaking ground on a new residential community, an architect writing specs for a client, a contractor hired to reroof, or a home inspector providing information to a potential homebuyer, it’s imperative to understand how to calculate if there is enough attic ventilation if you want that system to perform optimally.
In general, the building code sets minimum requirements for attic ventilation and it also provides “exceptions” (that is, the code will allow less than minimum if specific conditions are met). To keep this article simple, we’ll focus on the code minimum as listed in the 2012 International Residential Building Code, (IRC), Section R806 – Roof Ventilation.1 Code minimum is 1 sq. ft. of Net Free Area for every 150 sq. ft. of attic floor space.
Here’s a Handy Shortcut While it’s good to know where the attic ventilation calculations come from – especially if your customer asks for an explanation – you may be pressed for time in some instances and cannot afford to go through the 5-step calculations just reviewed. Good news. Here’s a handy shortcut to the math. Attic sq. ft. ÷ 2 = sq. in. of intake NFA and exhaust NFA needed @ 1/150 ratio.2 Go back to Step 1. We used a 2,000 sq. ft. attic as our example. Now apply the shortcut. • 2,000 sq. ft.
