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CITY OF EVERETT BUILDING DEPARTMENT <br />POLICY <br />The use of "bird blocking" to provide attic ventilation does not conform to <br />Section 3205(c) of the UBC unless it is used with a continuous ridge vent <br />or gable end vents. Three triangular cut-outs 3" wide x 12" high provide <br />3.375 square inches of net free area. Three 2" diameter holes provide <br />4.7 square inches of net free area.* An attic space of 1000 square feet <br />above a 25' x 40' house requires 6.67 square feet or 950 square inches of <br />net free area. That translates to 204 bird blocks or 102 per side, yet there <br />is only room for 20 per side so the inadequacy is obvious. <br />*Insect screen reduces gross area by one half. <br />