- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 18 Feb 2018
The thermal resistance of a material is a measure of how resistant it is to the transfer of heat across it. The thermal resistance of a material is measured by its R-value. The higher the R-value of a material, the more effective it is as an insulator.
For more information, see R-value.
Thermal resistance is the temperature difference between two defined material surfaces that induces a unit heat flow rate through a unit area. It is often described as the reciprocal of thermal transmittance, and can be derived from the thermal conductivity and the thickness of the materials.
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 not directly relatable to U-values however, as unlike U-values, R-values do not include surface heat transfers at the boundary of the element by convection and radiation, they are only a measure of the thermal resistance of the materials themselves.
 Find out more
 Related articles on Designing Buildings Wiki
Featured articles and news
Do you know your Rococo from your De Stijl, your Gothic from your Post-modernist?
May outlines a new funding strategy for housing associations and says the 'stigma' of social housing needs to end.
RIBA launches a consultation on a new Plan of Work for Fire Safety.
This article offers some basic rules to follow when writing your next specification.
The iconic Mackintosh Building will definitely be rebuilt, board chairwoman confirms.
The machinery used to fashion stone has changed dramatically - and so have the products.
This type of pile provides support to the building, as well as acting as a heat source and a heat sink.
Why investors are adopting the SDGs and why civil engineering could be crucial for delivering them.
Read about all the winners from the London ceremony of CIAT's 2018 Architectural Technology Awards.
How do you find the right stone to conserve historic buildings?
Appointment agreements often include a ‘scope of services’ setting out the consultant's performance on a project.