R-value
R-value measures a material's resistance to heat flow; a higher R-value means better insulating performance for that layer.
R-value measures a material's resistance to heat flow; a higher R-value means better insulating performance for that layer.
Definition
R-value is a measure of thermal resistance. It tells you how well a layer of material resists conduction of heat. Higher numbers mean more resistance, and values add up when layers are stacked in series.
A plain example
If one layer of insulation has a given R-value and a second layer is added, the total for those two layers is the sum of the two. Always read the unit system shown on the data sheet, since values are published in more than one system.
Why it matters
Energy codes and specifications often set minimum R-values, so it is a number you will see on drawings and product sheets. It helps compare insulation products on a like-for-like basis for a given thickness and condition.
Common confusion
R-value describes a material, while the wall delivers something different once framing, gaps and fasteners are in the picture. That whole-assembly view is why designers also use U-factor. R-value is also not a measure of air leakage or moisture control.
On a project
When comparing products, check the thickness, the test conditions and the unit system behind each R-value. Then ask how the designer accounts for framing in the wall total.
Quick answers
- Does a higher R-value always mean a better wall? Not on its own. Thermal bridging, air leakage and moisture also affect real performance.
- How is R-value related to U-factor? They are reciprocal ideas: U-factor describes heat flow through an assembly, and thermal resistance is its inverse.
- Where do required R-values come from? From the energy code adopted in your jurisdiction. Confirm with the designer and local authority.
Related terms
Always check the project drawings and specification, and confirm requirements with the engineer of record and the local authority.
Questions people ask
Does a higher R-value always mean a better wall?
Not on its own. Thermal bridging, air leakage and moisture also affect real performance.
How is R-value related to U-factor?
They are reciprocal ideas: U-factor describes heat flow through an assembly, and thermal resistance is its inverse.
Where do required R-values come from?
From the energy code adopted in your jurisdiction. Confirm with the designer and local authority.
Sources and further reading
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