Estimate attic insulation quantity from attic size, target R-value, existing R-value, bag coverage, and waste allowance. This calculator helps plan blown-in or batt insulation purchases before checking local energy code and product coverage charts.
Use consistent units and round materials up before ordering.
The calculator multiplies attic length by width for total area. Added R-value is the target R-value minus existing R-value. Order area adds the selected waste allowance, then divides by bag coverage to estimate the number of bags.
Example: a 40 ft by 30 ft attic is 1,200 square feet. Moving from R-19 to R-49 requires R-30 of added insulation. With 10% waste and 40 square feet of coverage per bag, the estimate rounds to 33 bags.
| Item | Planning value | Note |
|---|---|---|
| Attic target | Often R-38 to R-60 | Climate zone dependent |
| Waste allowance | 5%-10% | Uneven coverage and framing |
| Vent baffles | At soffits | Preserve airflow |
| Air sealing | Before insulation | Improves performance |
Order insulation by product coverage at the required installed depth, not just by bag count. Include baffles, rulers, air-sealing foam, caulk, protective gear, and equipment rental when needed.
Divide the attic order area by the product coverage per bag at your required R-value and round up.
Often yes if the old insulation is dry, clean, and not blocking ventilation, but damaged or contaminated material should be addressed first.
Recommended R-values depend on climate zone and local code. Use this calculator for quantity planning after choosing a target.
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