The R-Value is a measure of thermal resistance of a material's ability to resist heat flow.

Heat Flow

R-Value, Total R-Value and Added
R-Value are terms that are used within the Building Industry.

These terms are on or in; Working Drawings, House Energy Rating documentation, insulation products and insulation supplier's brochures.

It is important to understand which term relates to what process. Applying the wrong R-Value could mean that the project won't meet the current NCC's, Building Codes of Australia.

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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.

The Total R-Value of a Brick Veneer Wall with all of its components as listed below is R2.68. Notice how the Reflective Paper has no R-Value, it is a misconception that Reflective Paper has a R-Value of R1.3.

Component R-Value
1. Outdoor Air Film R0.04
2. 110mm Brickwork R0.14
3. 50mm Air Cavity R0.28
4. Reflective Paper R0.00
5. Wall Batt R2.00
6. Plasterboard R0.10
7. Indoor Air Film R0.12
Total R-Value R2.68
Brick Wall

Total R-Value R1.28 - A Brick Veneer Wall with no Wall Batts now has extra 90mm stud void with a value of R0.60.

Total R-Value R0.56 - A Brick Veneer Wall with no Wall Batts and no Reflective Paper now combines the 90mm stud void and the 50mm Air Cavity into one area with a value of only R0.16.

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 entered.

If Total R-Values are entered into the software program instead of Added R-Values then the Assessment might be under the minimum Star Rating required. This could mean that a 6 Star Rating is really only a 5.8 Star Rating.