Frequently Asked Questions
What target R-value should I use?
Check the U.S. Department of Energy recommendation for your climate zone. Attics commonly target R-38 to R-60.
How is insulation thickness calculated?
Divide the added R-value you need (target minus current) by the chosen material R-value per inch to get the required thickness in inches.
Why does spray foam need fewer inches than batts?
Closed cell spray foam has a high R-value per inch (about 6.5), so it reaches a target with less thickness than fiberglass batt at about 3.1.
What are board-feet?
A board-foot is a volume of one square foot at one inch thick. It is a convenient way to estimate how much insulation material to order.
Does air sealing matter before adding insulation?
Yes. Seal gaps, penetrations, and attic bypasses before adding insulation, or air leakage will let the assembly underperform its rated R-value.
Can I mix insulation types?
Yes. A common method is spray foam to air seal and batt or cellulose on top to build up the total R-value at a lower cost per square foot.
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Estimates for informational purposes only.
Important Disclaimer: Estimates for informational purposes only.
This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.