Solar Gain Coefficient (g-value)
In the context of windows and glazing, the g-value, also known as the solar heat gain coefficient (SHGC), represents the fraction of solar radiation (both directly transmitted and absorbed and then reradiated) that enters a building through a window or glazed surface. It is expressed as a number between 0 and 1, with higher values indicating a greater ability to transmit solar heat into a building.
The Importance in SAP
The more solar energy that enters a building, the less space heating that is required in the winter. But, in the summer this can lead to overheating.
Like everything in energy modelling, there needs to be a balance. That is why overheating needs to be assessed at planning stage and a full design is carried out to avoid issues further down the building process.
Other Considerations
- Acoustic Attenuation
- U-values
- Off-set/ Thermal bridging
- Passive Ventilation
- Purge Ventilation
- Means of Escape
