Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca.
Estimating ventilation requirements for attic.
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.
The federal housing authority fha and the urban development hud have established minimum requirements for attic ventilation.
So we would need at least six metal vents in addition to the lower soffit ventilation to meet minimum ventilation requirements.
If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation.
Of vent for every 300 sq.
There should also be a 50 50 balance of attic venting and roof venting.
Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed.
Ventilation can be accomplished using various products and techniques.
Measure the length and width of the attic floor space to be ventilated.
A normal metal pot vent produces only 50 squares inches of free net area.
The calculations before indicated that we needed 2 square feet of ridge or upper roof ventilation.
Let owens corning roofing help you calculate exactly how much ventilation you will need for a healthy and balanced attic with our 4 step ventilation calculator.
This shortcut conveniently calculates the 2015 international residential building code minimum irc section r806 roof ventilation 1 which states in part 1 square foot of net free area for every 150 square feet of attic floor space with the attic defined as length x width floor of the attic.
For large volume attics such as where roof slopes are greater than 8 12 designers also should consider increasing.
Most building codes require a ratio of 1 150 ventilation space to attic floor space.
As an example in an attic that is 30 feet by 20 feet you would have 600 square feet of floor area.
Hence you would need two square feet 600 300 of attic ventilation.
In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq.
According to the national roofing contractors association nrca a power vent with an airflow rate of 1 0 cubic foot per minute per square foot of attic space measured at the attic floor is generally considered to be equivalent to a 1 150 ventilation ratio.
Two square feet equals 288 square inches.
