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
Latest Build UK Building Safety Regime explainer published
Key elements in one short, now updated document.
UKGBC launch the UK Climate Resilience Roadmap
First guidance of its kind on direct climate impacts for the built environment and how it can adapt.
CLC Health, Safety and Wellbeing Strategy 2025
Launched by the Minister for Industry to look at fatalities on site, improving mental health and other issues.
One of the most impressive Victorian architects. Book review.
Common Assessment Standard now with building safety
New CAS update now includes mandatory building safety questions.
RTPI leader to become new CIOB Chief Executive Officer
Dr Victoria Hills MRTPI, FICE to take over after Caroline Gumble’s departure.
Social and affordable housing, a long term plan for delivery
The “Delivering a Decade of Renewal for Social and Affordable Housing” strategy sets out future path.
A change to adoptive architecture
Effects of global weather warming on architectural detailing, material choice and human interaction.
The proposed publicly owned and backed subsidiary of Homes England, to facilitate new homes.
How big is the problem and what can we do to mitigate the effects?
Overheating guidance and tools for building designers
A number of cool guides to help with the heat.
The UK's Modern Industrial Strategy: A 10 year plan
Previous consultation criticism, current key elements and general support with some persisting reservations.
Building Safety Regulator reforms
New roles, new staff and a new fast track service pave the way for a single construction regulator.
Architectural Technologist CPDs and Communications
CIAT CPD… and how you can do it!
Cooling centres and cool spaces
Managing extreme heat in cities by directing the public to places for heat stress relief and water sources.
Winter gardens: A brief history and warm variations
Extending the season with glass in different forms and terms.
Restoring Great Yarmouth's Winter Gardens
Transforming one of the least sustainable constructions imaginable.
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