Insulation Options for Energy-Efficient Homes: A Builder's Comparison
Understanding R-Value and Beyond
R-value measures thermal resistance, but it does not tell the whole story. Air sealing, moisture management, thermal bridging, and installation quality all affect real-world energy performance. A wall with R-19 fiberglass batts that are compressed around wiring and poorly fitted around outlets may perform worse than an R-13 wall with meticulous air sealing and continuous insulation that eliminates thermal bridges at studs.
Insulation Material Comparison
Fiberglass batts remain the most affordable option at $0.50-1.00 per square foot installed but require careful installation to avoid gaps and compression. Blown cellulose excels at filling irregular cavities and costs slightly more while providing better air sealing. Closed-cell spray foam delivers the highest R-value per inch (R-6.5) and doubles as an air and vapor barrier, but at three to four times the cost of fiberglass. Mineral wool batts offer superior fire resistance and sound attenuation with easy, forgiving installation.
Assembly-Level Thinking
The most effective approach considers the entire wall, roof, or floor assembly rather than just the cavity insulation. Continuous exterior insulation—rigid foam board or mineral wool—breaks the thermal bridge at framing members and can add R-5 to R-10 to the assembly's performance. Combined with an effective air barrier and proper vapor control for your climate zone, this approach consistently outperforms simply increasing cavity insulation depth.