SAP Overglazed Extensions

When building a residential extension, you may be required to show compliance with Part L of the Building Regulations.

If your proposed extension has more glazing (windows, doors or rooflights) than 25% of the new floor area, you will need a SAP Calculation to comply with Part L Building Regulations. Due to increased heat loss through glazing as opposed to insulated walls or roofs there are restrictions in the building regulations to the area of glazing permissible within an extension. to prevent excessive heat loss and energy inefficiency.

​To meet the regulations, you must show that your extension will not increase CO₂ emissions of the dwelling more than a Building Regulations compliant extension.

Our SAP Calculations demonstrate that, by making energy-saving improvements elsewhere in your home, your proposed extension will perform as well as — or better than — a standard, compliant extension.