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
ECA Industry Awards 2024 shortlist revealed
22 leading businesses from across the electrotechnical and engineering services sector.
Government unveils Skills England strategy
Skills England to transform opportunities and drive growth.
New Government Hub for York Given Planning Green Light
For up to 2,600 civil servants, due for completion by 2028.
Construction Skills Certification Scheme cards
July update on Professionally Qualified and Academically Qualified Person Cards.
BSRIA Briefing 2024, November 22
Sustainable Futures: Redefining Retrofit for Net Zero Living.
The CLC on driving competency in the retrofit sector
Previously published roadmap on skills for net zero.
The first labour government King's speech in fifteen years
Construction industry reactions, support and some concern.
CIOB Retrofit of Buildings Technical Information Sheet
What retrofit is, the approach to be taken and processes to be followed.
Adapting Historic Buildings for Energy and Carbon Efficiency
Historic England advice note 18, free download published.
10 retrofit projects revisited 10 years after completion.
Information orders, building liability orders and SPVs
Key BSA terms and how they impact special purpose vehicles.
Listed despite problems with its design.
Zen and the art of cycling exploration.
Design Council Homes Taskforce launched
To support government 1.5 million homes target within UK climate commitments.
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