Energy
Compressing Insulation Destroys Most of Its Value
An R-19 batt crushed into a 2x4 cavity performs at roughly R-13 — you pay for R-19 and install R-13.
Fibreglass and mineral wool do not insulate because the fibres resist heat. They insulate because the fibre matrix immobilises air, and still air is an excellent insulator. Compression reduces the volume of trapped air while keeping the same mass of conductive fibre, so performance falls disproportionately.
The corollary matters just as much: gaps, tucks around wiring, and batts stuffed behind pipes create bypasses that let air move. A carefully fitted R-13 batt regularly outperforms a carelessly stuffed R-19 one.
Put this into practice
- Insulation R-Value CalculatorWhat R-value do I need, and how much?
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