- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 01 Dec 2019
Thermal conductivity (sometimes referred to as k-value or lambda value (λ)) is a measure of the rate at which temperature differences transmit through a material. The lower the thermal conductivity of a material, the slower the rate at which temperature differences transmit through it, and so the more effective it is as an insulator. Very broadly, the lower the thermal conductivity of a building's fabric, the less energy is required to maintain comfortable conditions inside.
The U value of an element of a building can be calculated from sum of the thermal resistances (R-values) of the layers that make up the element plus its internal and external surface resistances (Ri and Ro).
U-value = 1 / (ΣR + Ri + Ro)
The standards for the measurement of thermal conductivity are BS EN 12664, BS EN 12667 and BS EN 12939. In the absence of values provided by product manufacturers following thermal conductivity tests, the thermal conductivity data obtained from BS EN 12524 Building materials and products. Hygrothermal properties.
 Thermal conductivity of typical building materials
|glass foam aggregate (dry)||0.08|
|phenolic foam (PIR)||0.020|
|polyurethane foam (PUR)||0.025|
|steel||16 - 80|
|stone (granite)||1.7 - 4.0|
|timber (hardwood - commonly used)||0.14 - 0.17|
 Related articles on Designing Buildings Wiki
Featured articles and news
Cutting-edge tech pairs with building management systems.
BSRIA updates its assessment of the industry.
What happens when it all goes wrong?
Input being gathered by CIOB.
Changes proposed for MHCLG consultation on house building statistics.
Full of passion and acerbic wit. 1 min book review.
Reminding us what is possible.
Five signs you are at risk.
Biotechnology as it applies to the built environment.
Stopping sound coming through windows.
Government response to the Building a Safer Future consultation.
Energy savings quickly payback any small additional capital investment.
Overbuild and air-space developments.