impact of glazing on SAP assessment

In this article I intend to deal with the three parameters commonly effecting adverse SAP assessments. This is not intended to be a definitive statement on glazing for that view SAP 2009 – Th Government’s SAP for Energy Rating of Dwellings

The three parameters are:

  • U Value of entire window
  • ‘G factor’ of the glass
  • Summer overheating and the air flow rate

The U Value of the entire window is important to the efficiency of the building especially if the building is to have a large amount of glass however; the better the U Value the higher the cost. The openings in the building must not have a U Value greater than 2.0 (bear in mind an average door has a U Value of around 3.0)

The amount of heat the glazing lets into the dwelling, the G Factor, is dependent upon the coating put on the glass. The lower the G Factor, the better the glass is a resisting heat transfer, but the higher the energy used to heat the dwelling.

If the G Factor is to high the dwelling will fail due to summer over heating and if it is to low the amount of energy required to heat the building will be to large causing a DER/TER failure

Should there be a requirement to use renewable sources to provide say 15% of energy then the lower the G Factor, the lower energy requirement and therefore the lower the renewables required

If you require assistance on exactly how to balance these factors contact us

Leave a Reply

Your email address will not be published. Required fields are marked *