If the crack is in your ceiling hot air in the attic can draw/suck cold conditioned air out. It happens through a natural principle of science call convection.
Net free venting requirements for residential construction states that we should provide a “balanced” air flow for attic ventilation. 50% of the air needed to cool your attic should enter at the edge of the roof…down near the windows. 50% of the required openings should be as high as
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For at least the last twenty years or so, the most common way of insulating attics in Minnesota is to use loose-fill insulation – either cellulose or fiberglass. This is a huge improvement over fiberglass batts, because batts are nearly impossible to install in attics and they cost more money. Despite the decline of fiberglass batts in attics, I still find a small section of fiberglass batting used above the attic access panel at about 90% of the homes that I inspect, even on new construction.