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SAP Calculations for Extensions.  

L1B – SAP calculations for heavily glazed extensions

If you build an extension where the glazing is greater than 25% of the floor area, then we can undertake a SAP assessment to demonstrate compliance with Approved Document L1B.

Using SAP, we can provide you with an economic and feasible solution to ensure your extension achieves compliance, no matter how much glazing you wish to include in the design.


Three steps to compliance:

  1. Use SAP to calculate the CO2 emissions for the existing house along with the proposed extension.

  2. Calculate the CO2 emissions for the existing house with a notional extension. A notional extension is an extension that meets the minimum standards of Approved Document L1B.

  3. Compliance is achieved provided the “proposed” CO2 emissions are no greater than the “notional” CO2 emissions.


In a Nutshell. 

We will assess the extension based on the design-specification provided.

The vast majority of projects we assess achieve a pass first time. If a pass is not achieved we will recommend certain cost effective options to achieve a pass. For example, increase in insulation, improved performing glazing, or improvements to the existing dwelling.

Once a satisfactory specification has been agreed we will issue a copy of the SAP reports for submission to Building Control.


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