- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 23 Mar 2017
R-values are a measure of the thermal resistance of a material of a specific thickness, that is, its resistance to the transfer of heat across it. The higher the R-value of a material, the more effective it is as an insulator.
R-values can be used as part of a labelling system to enable comparison of the thermal performance of different materials, such as insulation, or as part of the calculation of heat transfer across the fabric of a building.
R-values can be calculated by dividing the thickness of a material (in metres) by its thermal conductivity (k-value or lambda value (λ) in W/mK). R-values are therefore expressed in m2K/W (or ft2·°F·hr/Btu in the USA). The overall R-value of a multi-layered element can be calculated by adding the R-values of its component materials.
R-values are sometimes described as being the reciprocal of U-values (sometimes referred to as heat transfer coefficients) which describe the thermal conductivity of a building element. However, unlike U-values, R-values do not include surface heat transfers at the boundary of the element by convection and radiation.
 Find out more
 Related articles on Designing Buildings Wiki
Featured articles and news
Their survival against the odds is a remarkable feature of the City’s history.
Immersed, charmed and inspired on conservation’s front line.
About JCT...and the rest
The Centre Building, London School of Economics
Architecture course essentials
Enhancing employee health and wellbeing
Underfloor heating opportunities as world radiator market cools.
Points to consider to make specifying sustainable.
It is not just about speed
The Flatiron Building, New York
Which way up should you lay a brick?