R-Values
The R-Value is a measure of thermal resistance of a material's ability to resist heat flow: R-Value = Thickness (m) / Thermal conductivity (W/mK) |
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Total R-Value, Added R-Value and |
Total R-Values
A Total R-Value is the sum of the R-values of the individual component's within a structure, for example a brick veneer wall. The Total R-Value includes any building materials, insulation materials, airspaces and internal/external air film surfaces.
Total R-Value R2.68: The Brick Veneer Wall below with all of its components as listed below has a Total R-Value of R2.68, notice how the Reflective Paper has no R-Value.
It is a misconception that Reflective Paper has an independent
R-Value of R1.3, the R1.3 is the result of a Total R-Value as
explained below.
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Total R-Value R1.28: The Brick Veneer Wall above with no Wall Batt now has an extra 90mm stud void and the reflective paper now comes into play with only an added R0.60 to the Total R-Value.
Total R-Value 2.68 - R2.00 + R0.60 = Total R-Value 1.28
Total R-Value R0.56: The Brick Veneer Wall above with no Wall Batt and no Reflective Paper, now combines the 90mm stud void with the 50mm Air Cavity into one void area with only an added R0.16 to the Total R-Value.
Total R-Value 1.28 - R0.60 - R0.28 + R0.16 = Total R-Value 0.56
Added R-Values
The term Added R-Values is generally related to wall, ceiling/roof and sub/floor insulation products.
The software programs that perform House Energy Ratings (Thermal Performance Assessments) automatically calculate the wall, ceiling/roof and sub/floor Total R-Values so only the Added R-Value of the insulation product is required to be entered.
If the Total R-Values are entered into these software programs instead of the Added R-Values then the Assessment will most likely fail compliance when corrected.