Thermal conductivity
[edit] Introduction
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.
Thermal conductivity is a fundamental material property independent of thickness. It is measured watts per meter kelvin (W/mK).
The thermal resistance of the layers of the a building's fabric (R measured in in m²K/W) can be calculated from the thickness of each layer / the thermal conductivity of that layer.
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)
U-values (sometimes referred to as heat transfer coefficients or thermal transmittances) are used to measure how effective elements of a buildings fabric are as insulators.
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.
[edit] Thermal conductivity of typical building materials
Thermal conductivity values of typical building materials shown below.
Material | W/mK |
Blockwork (light) | 0.38 |
Blockwork (medium) | 0.51 |
Blockwork (dense) | 1.63 |
Brick (exposed) | 0.84 |
Brick (protected) | 0.62 |
Chipboard | 0.15 |
Concrete (aerated) | 0.16 |
Concrete (cellular 400 kg/m3) | 0.1 |
Concrete (cellular 1200 kg/m3) | 0.4 |
Concrete (dense) | 1.4 |
fibreglass quilt | 0.033 |
glass | 1.05 |
glass foam aggregate (dry) | 0.08 |
hemp slabs | 0.40 |
hempcrete | 0.25 |
mineral wool | 0.038 |
mortar | 0.80 |
phenolic foam (PIR) | 0.020 |
plaster (gypsum) | 0.46 |
plasterboard (gypsum) | 0.16 |
polystyrene foam | 0.032 |
polyurethane foam (PUR) | 0.025 |
render (sand/cement) | 0.50 |
screed (cement/sand) | 0.41 |
steel | 16 - 80 |
stone (limestone) | 1.30 |
stone (sandstone) | 1.50 |
stone (granite) | 1.7 - 4.0 |
stone chippings | 0.96 |
straw bale | 0.09 |
timber (softwood) | 0.14 |
timber (hardwood - commonly used) | 0.14 - 0.17 |
woodfibre board | 0.11 |
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Private rental sector, living standards and fuel poverty
Report from the NRH in partnership with Impact on Urban Health.
.Cold chain condensing units market update
Tracking the evolution of commercial refrigeration unit markets.
Attending a conservation training course, personal account
The benefits of further learning for professsionals.
Restoring Alexander Pope's grotto
The only surviving part of his villa in Twickenham.
International Women's Day 8 March, 2025
Accelerating Action for For ALL Women and Girls: Rights. Equality. Empowerment.
Lack of construction careers advice threatens housing targets
CIOB warning on Government plans to accelerate housebuilding and development.
Shelter from the storm in Ukraine
Ukraine’s architects paving the path to recovery.
BSRIA market intelligence division key appointment
Lisa Wiltshire to lead rapidly growing Market Intelligence division.
A blueprint for construction’s sustainability efforts
Practical steps to achieve the United Nations Sustainable Development Goals.
Timber in Construction Roadmap
Ambitious plans from the Government to increase the use of timber in construction.
ECA digital series unveils road to net-zero.
Retrofit and Decarbonisation framework N9 launched
Aligned with LHCPG social value strategy and the Gold Standard.
Competence framework for sustainability
In the built environment launched by CIC and the Edge.
Institute of Roofing members welcomed into CIOB
IoR members transition to CIOB membership based on individual expertise and qualifications.
Join the Building Safety Linkedin group to stay up-to-date and join the debate.
Government responds to the final Grenfell Inquiry report
A with a brief summary with reactions to their response.
Comments
Thermal conductivity (often denoted k, λ, or κ) refers to the intrinsic ability of a material to transfer heat. It is evaluated primarily in terms of Fourier’s Law for heat conduction. https://thermtest.com/what-is-thermal-conductivity