Wet, contaminated, or rodent-damaged insulation: yes, removed and disposed. Dry clean fiberglass can sometimes be left under foam, but most retrofits benefit from removal first. Removal runs $0.50-$1.00/sq ft.
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Removal cost depends on attic accessibility and existing insulation type. Loose-fill blown insulation (cellulose, fiberglass) is removed via a vacuum truck for $0.75-$1.50/sqft. Fiberglass batts are pulled out and bagged for $0.50-$1.00/sqft. Disposal goes to standard construction-debris facilities (not hazardous waste). When removal is recommended: any wet or evidently mold-contaminated insulation, any insulation with rodent activity, any insulation that has been compressed below half its original loft, and any case where the homeowner wants the cleanest possible re-insulation. When leaving in place is OK: dry clean fiberglass batts in attic floor when planning to spray closed-cell on the roof deck (creating a hybrid assembly with foam air-seal plus existing fiberglass R-value). Our Cincinnati installers identify and recommend the right approach during the on-site assessment. Cincinnati removal-coordination tip: when our technician has same-week capacity, scheduling removal the day before spray application eliminates one project visit and reduces total labor cost. When removal and foam happen on consecutive days, the homeowner sees a single staging period with both crews on site during overlapping hours. The schedule efficiency saves $100-$300 on typical projects.