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
HBPT and BEAMS Jubilees. Book review.
Does the first Labour budget deliver for the built environment?
What does the UK Budget mean for electrical contractors?
Mixed response as business pays, are there silver linings?
A brownfield housing boost for Liverpool
A 56 million investment from Homes England now approved.
Fostering a future-ready workforce through collaboration
Collaborative Futures: Competence, Capability and Capacity, published and available for download.
Considerate Constructors Scheme acquires Building A Safer Future
Acquisition defines a new era for safety in construction.
AT Awards evening 2024; the winners and finalists
Recognising professionals with outstanding achievements.
Reactions to the Autumn Budget announcement
And key elements of the quoted budget to rebuild Britain.
Chancellor of the Exchequer delivers Budget
Repairing, fixing, rebuilding, protecting and strengthening.
Expectation management in building design
Interest, management, occupant satisfaction and the performance gap.
Connecting conservation research and practice with IHBC
State of the art heritage research & practice and guidance.
Innovative Silica Safety Toolkit
Receives funding boost in memory of construction visionary.
Gentle density and the current context of planning changes
How should designers deliver it now as it appears in NPPF.
Sustainable Futures. Redefining Retrofit for Net Zero Living
More speakers confirmed for BSRIA Briefing 2024.
Making the most of urban land: Brownfield Passports
Policy paper in brief with industry responses welcomed.
The boundaries and networks of the Magonsæte.
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