Which insulation type provides the highest R-value per inch of thickness?
Correct Answer
C) Polyurethane spray foam
Polyurethane spray foam provides the highest R-value per inch (R-6 to R-7) compared to other common insulation materials. It also provides air sealing properties and adheres well to irregular surfaces.
Why This Is the Correct Answer
Polyurethane spray foam provides the highest R-value per inch of thickness among common insulation materials, typically ranging from R-6 to R-7 per inch. This closed-cell foam creates an excellent thermal barrier while also providing superior air sealing properties. Its ability to expand and fill gaps makes it highly effective at preventing thermal bridging and air infiltration, which significantly enhances overall energy efficiency beyond just the R-value rating.
Why the Other Options Are Wrong
Option A: Fiberglass batts
Fiberglass batts provide only R-3.1 to R-3.4 per inch, which is roughly half the R-value of spray foam insulation.
Option B: Cellulose blown-in
Cellulose blown-in insulation provides approximately R-3.6 to R-3.8 per inch, which is significantly lower than spray foam's R-6 to R-7 per inch.
Option D: Polystyrene rigid board
Polystyrene rigid board provides R-4 to R-5 per inch, which is good but still lower than polyurethane spray foam's R-6 to R-7 per inch.
Memory Technique
Think 'SPRAY PAYS' - spray foam pays off with the highest R-value per inch, making it the premium choice for maximum thermal performance in limited space.
Reference Hint
Florida Building Code - Energy Conservation, Chapter 11 (Energy Efficiency) or ASHRAE 90.1 insulation tables
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