NASCLA Accredited Commercial General ContractorThermal and Moisture ProtectionEasy
A contractor is installing insulation in the roof assembly of a commercial building. The building code requires a minimum R-value of 30. The selected insulation material has an R-value of 4.5 per inch. If the contractor uses 6 inches of this insulation, what is the total R-value achieved, and does it meet the code requirement?
- ATotal R-value = 28.5; Does not meet requirement.
- BTotal R-value = 30; Meets requirement.
- CTotal R-value = 27; Does not meet requirement.
- DTotal R-value = 32.5; Meets requirement.
Show answer & explanationAnswer & explanation
Correct answer: C. Total R-value = 27; Does not meet requirement.
To calculate the total R-value, multiply the R-value per inch by the insulation thickness: 4.5 R-value/inch * 6 inches = 27 R-value. This is less than the required R-30.
Why the other options are wrong
- A. Incorrect calculation and conclusion.
- B. Incorrect calculation and conclusion.
- D. Incorrect calculation and conclusion.
Total R-value Calculation
The total thermal resistance of an insulation layer is calculated by multiplying its R-value per inch by its total thickness in inches.
- R-value is a measure of thermal resistance.
- Higher R-value means better insulation.
- Units are typically (ft²·°F·h)/BTU.
- Required R-values vary by climate zone and building code.
Memory trick: R-value is 'Rate' times 'Reach' (thickness).