Thermal indices for the built environment
This page presents a summary of thermal indices used in the construction industry. For more information go to the articles for each item. To add more items, click 'Edit this article' above.
Degree days. The number of days and degrees that the outside air temperature is above or below a specified base temperature. See Heating degree days.
Emissivity. The amount of long wave infra-red radiation which a surface of known temperature (such as the façade of a building) will emit to its surroundings.
g-value (sometimes referred to as window solar factor, solar factor or total energy transmittance (TET)). The fraction of incident solar radiation transmitted by a window, expressed as a number between 1 and 0, where 1 indicates the maximum possible solar heat gain, and zero, no solar heat gain. NB The difference between g-values and solar heat gain coefficients is that they use a different value for air mass.
k value (or lambda value λ). A measure of the intrinsic thermal conductivity of a material, that is, how easily heat passes across it. This is a fundamental property independent of thickness.
Predicted percentage dissatisfied.
Psychometric charts. Graphs that can be used to assess the physical and thermodynamic properties of gas-vapour mixtures at a constant pressure.
R-value. A measure of the thermal resistance of a material of a specific thickness.
Shading coefficient. The amount of solar heat that passes through a transparent or translucent material compared to the amount of solar heat that passes through a sheet of clear float glass with a total solar heat gain coefficient of 0.87 (ie a sheet of clear float glass 3mm thick which has a shading coefficient of 1).
Solar heat gain coefficient. The fraction of incident solar radiation transmitted by a window, expressed as a number between 1 and 0, where 1 indicates the maximum possible solar heat gain, and zero, no solar heat gain. NB The difference between g-values and solar heat gain coefficients is that they use a different value for air mass.
Temperature. A measure of the average kinetic energy of molecules.
Thermal comfort. ‘…that condition of mind which expresses satisfaction with the thermal environment’.
Thermal optical properties. Characteristic radiant behaviour within the thermal spectrum.
U-value (or heat transfer coefficient). A measure of the thermal conductivity of a complete building element, including its surface conductivities.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
For the World Autism Awareness Month of April.
70+ experts appointed to public sector fire safety framework
The Fire Safety (FS2) Framework from LHC Procurement.
Project and programme management codes of practice
CIOB publications for built environment professionals.
Sustainable development concepts decade by decade.
The regenerative structural engineer
A call for design that will repair the natural world.
Buildings that mimic the restorative aspects found in nature.
CIAT publishes Principal Designer Competency Framework
For those considering applying for registration as a PD.
BSRIA Building Reg's guidance: The second staircase
An overview focusing on aspects which most affect the building services industry.
Design codes and pattern books
Harmonious proportions and golden sections.
Introducing or next Guest Editor Arun Baybars
Practising architect and design panel review member.
Quick summary by size, shape, test, material, use or bonding.
Types of rapidly renewable content
From forestry to agricultural crops and their by-products.
Terraced houses and the public realm
The discernible difference between the public realm of detached housing and of terraced housing.