Can you put too much insulation in your attic?

You can put too much insulation in your attic in the sense of causing problems, but you cannot have too much R-value if it is installed correctly with proper ventilation and air sealing. Problems occur when insulation is piled so high that it blocks soffit vents, which are critical for attic ventilation to remove moisture and prevent ice dams and roof rot. If blown insulation covers soffit vents, the attic cannot breathe and moisture accumulates. Another problem is when insulation is stuffed into eaves and contacts the roof deck, creating a cold spot or trapping moisture. Excessive weight can also be a concern, particularly with dense cellulose at 1.5 to 2 pounds per square foot when piled 20 plus inches, though most attics can support it. Compression is another issue, if you stack batts and compress lower layers you actually lose R-value. From an energy perspective, beyond about R-60, adding more insulation has very small additional savings and the money is better spent elsewhere. So you cannot have too much thermal resistance in principle, but you can have improper installation where too much material in the wrong place blocks ventilation, covers electrical fixtures not rated for contact, or causes moisture issues.