Regulations made under sections 58B and 58C of Finance Act 2003 permit relief from Stamp Duty Land Tax for zero-carbon new homes.
First the dwelling CO2 emissions are calculated as for building regulations compliance. The calculations are then continued as described in the document "SAP 2005 extension for SDLT". The conditions for SDLT relief are:
A. The heat loss parameter must be no greater than 0.8 W/m²K
Some commercial SAP 2005 calculators include the zero-carbon additions. In other cases the spreadsheet on this web page can be used.