- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 16 Feb 2018
G-value in buildings
Understanding the solar transmittance through translucent and transparent materials such as glass is important for determining the solar heat gain into the space they enclose during sunny conditions. Solar heat gain can be beneficial in the winter, as it reduces the need for heating, but in the summer can cause overheating.
The total solar heat transmittance through transparent and translucent materials is equal to the solar heat that is transmitted through the material directly, plus the solar heat that is absorbed by the material and then re-emitted into the enclosed space.
Traditionally this was expressed in terms of a shading coefficient which described the amount of solar heat transmitted through a material compared to the amount of solar heat transmitted through a standard sheet of clear float glass 3 mm thick.
However, manufacturers are now moving away from shading coefficients. In the USA, they are moving towards the use of solar heat gain coefficients (SHGC) and in Europe, g-values (window solar factors, solar factors or total energy transmittance (TET)). In essence, these both represent 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.
g-values can refer to the centre-of-glass g-value, or can relate to the entire window, including frame (gglass or gwindow). Generally, a higher g-value will be beneficial in cooler climates and a lower g-value in warmer climates. Typically g-values will range between 0.2 and 0.7, with solar control glazing having a g-value of less than 0.5.
 Related articles on Designing Buildings Wiki
- Code for Sustainable Homes.
- Computational fluid dynamics (CFD).
- Emission rates.
- Energy certificates.
- Environmental legislation.
- Green deal.
- Leadership in Energy and Environmental Design.
- Low-e glass.
- Shading coefficient.
- Solar heat gain coefficient.
- Solar transmittance (gtot).
- Thermal bridge.
- Thermal resistance.
- U value.
- Zero carbon homes.
- Zero carbon non-domestic buildings.
Featured articles and news
A right to light generally refers to the right to receive sufficient light through an opening.
Interference and compatibility - the effects of electromagnetic fields in the workplace.
Important action is being taken to inspire young people to train as engineers.
A survey of Leicester’s historic buildings resulted in local listing being taken more seriously.
Demolition is the most high risk activity in the construction sector. Read our introductory article here.
BSRIA report on the domestic boiler market, with China recording the most 'dynamic market uptake'.
Do we really know everything important about the impacts of our infrastructure projects? And if we don’t, does it matter?
Former Chief executive Richard Howson blames government for being 'poor payers'.
An environmental plan is an essential tool for setting and managing environmental objectives for a project.
CLC call for an 'outcome-based, transparent and efficient' industry with new report.