- 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.
U-value = 1 / (the sum of the R-values of the layers of the element + the resistance of the internal and external surfaces of the element)
 Related articles on Designing Buildings Wiki
Featured articles and news
BRE partner with Global GreenTag to develop an Ethical Labour Sourcing Standard for Australia.
The Chartered Quality Institute explain the pathway to success for organisations implementing management systems.
An introductory article looking at where a duty of care can arise in the construction industry.
House of Lords committee encourages the use of off-site manufacturing in new report.
Computational fluid dynamics (CFD) can go some way to show the impact of new buildings on their surroundings.
The shortlist for the 2018 prize for the UK's best new building is revealed.
Amendment to Bill aims to provide councils with greater powers to increase tax premiums on empty homes.
As the latest summer blockbuster 'Skyscraper' is released, we look at some of the best uses of buildings in film.
Read our introductory article on how to layout a building.
New cross-party report calls for combustible cladding ban to be extended to all high-rise residential buildings.