This agency of the U.S. Department of Energy conducted an in-depth study of insulation behavior and thermodynamics in a common residential attic construction.
Conclusions:
- EPS insulation R-value remained constant throughout winter temperatures.
- Fiberglass insulation R-value decreased by 50% in winter conditions. Therefore, R-38 fiberglass insulation decreases to as low as R-19 during winter conditions.
In a typical roof attic, the fiberglass is in a non-sealed environment or non-steady state environment – unlike when it was tested in a laboratory. In winter conditions, cold air enters through attic roof vents. The OPEN CELL fiberglass allows the cold air to infiltrate the insulation, displacing warmer air pockets.
Pages
Part 1 - R-Values in Today's Building Codes
Part 2 - Designing R-Values: In the Lab
Part 3 - Air Infiltration
Part 4 - "Real Time" R-Values
Part 5 - Oak Ridge National Laboratory Study
Part 6 - Brock University Study
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