Attic Vent Insulation Requirements

1 300 ventilation ratio recommended.

Attic vent insulation requirements. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Calculate or enter the square footage of the attic or area to be vented. Industry standard for proper attic ventilation recommends for no vapor retarder type of attic insulation no paper plastic or aluminum layer between the attic floor and insulation layer 1 sq. Of vent for every 300 sq.

In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. The recommended ventilation ratio to provide for vented attic assemblies when an air barrier is present is the 1 300 ratio as specified by most building codes. Enter your square footage. For large volume attics such as where roof slopes are greater than 8 12 designers also should consider increasing.

Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation. Ventilation openings having a least dimension larger than 1 4 inch 6 4 mm shall be provided with corrosion resistant wire cloth screening hardware cloth perforated vinyl or similar material with openings having a least dimension of 1 16 inch 1 6 mm minimum and 1 4 inch 6 4 mm maximum. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow. You can also contact your local municipality to check on building code in your area.

In other words the entire vent opening doesn t count as vented space. Roof insulation thermal resistance at roof perimeter should be equal or greater to thermal resistance of exterior wall. Foot of ventilation for every 150 sq. Most building codes require a ratio of 1 150 ventilation space to attic floor space.

Feet of attic space divided 50 50 between the inlets and outlets. That said air resistance and interference such as vent grates reduces the area of true ventilation. Measure the length and width of the attic floor space to be ventilated.