Over Glazed Extensions from £300
The SAP Calculation required for Over Glazed Extensions is the more complicated than the calculation required for a New Build or Conversion. This is due to the fact that 2 calculations are required.
Existing Dwelling + A Notional Extension - This will show the dwelling as it stands plus an extension that has a glazing area that is only 25% of the floor area. The External Walls, Floor and Roof will show the minimum requirements to meet building regulations.
Existing Dwelling (With improvements) + The Actual Proposed Extension - This will show the Existing Dwelling with any improvements plus the extension how it is actually going to be built. The External Walls, Floor, and Roof are likely to be an improvement on the Notional Extension. This calculation will also show the true area of the glazing that is going to be installed. More details on the requirements for extensions can be found in Approved Document L1B
The idea of carrying out the 2 calculations is to show that the C02 emissions of the Dwelling plus the Actual Extension are no higher than the C02 emissions of the Dwelling plus the Notional Extension.