For extensions where the glazed area greater than the allowable area (25% of the new floor area plus the area of any existing openings that have been covered by the new extension) a whole house calculation is required to comply with SAP 2009.

Whole House Calculation

Where the extension and alterations to the existing dwelling are substantial the only way to produce a satisfactory result is to provide a whole house calculation for the existing dwelling plus a notional extension which complies with SAP 2009 and a further calculation of the dwelling plus the proposed extension together with any improvements planned for the existing dwelling. For the extension to pass, the CO2 emission rate from the dwelling with its proposed extension should not be greater than that of the dwelling plus the notional extension.

Notional Extension

This software calculates the notional extension from the dimensions provided, and will automatically calculate the carbon dioxide emissions for the existing dwelling with the proposed extension, and the existing dwelling with the notional extension.

  • Automatic calculation of the notional extension
  • Enter dimensions once only. Calculate notional and proposed in the same calculation
  • Allocate construction elements and windows to the extension or existing dwelling.

Improvements to Existing Dwelling

If  on first estimate the extension does not show compliance, it is permissible to improve the existing dwelling to achieve compliance. Eligible improvements are to the fabric, the heating system, or indeed any item which affects the carbon dioxide emissions. This can be time consuming for each change a new calculation is required for the notional and proposed extensions. The extension module solves this problem by incorporating all elements in a single calculation which is recalculated for both cases.

  • Update uvalues for existing dwelling elements and recalculate
  • Notional and proposed dwellings recalculated simultaneously on a change of existing.
  • Individual reports for the notional and proposed extensions

Example Calculation

The software includes an example calculation for a detached house with an integral garage and a floor area of 70 extension is proposed to the rear of the kitchen 4m long 3.5m wide. To produce a calculation for compliance with approved documents L1B the following steps undertaken.

  1. Create the calculation for the existing dwelling without the extension.
  2. Update the calculation to include the increased floor area including the extension
  3. Reduce the Wall area to account for the Wall which has been removed due to the addition.
  4. Mark any Windows has removed if they no longer exist.
  5. Add new windows or doors to the extension.

The software will automatically calculate the emissions for the dwelling with the new extension and the dwelling with the notion extension including all glazing. The report page will show you the results of the calculation and whether compliance has been achieved.