Part L1B Large Glazed Extensions & Conversions


  • If the glazing of a proposed extension is greater than 25% of the extension internal floor area, then a SAP calculation will generally be required. (If the extension is unheated and separated from the main dwelling by patio doors then a SAP calculation is not required).

  • The calculations compare a compliant (notional) extension design (including the existing dwelling) against the proposed extension (including the existing dwelling with any improvements proposed).

  • Compliance is achieved if the proposal produces less Co2 emissions is no worse than the compliant notional option.

Conversions/Material Change Of Use…

  • If the proposed dwelling is deemed to be a material change of use, a SAP assessment will be required.

  • An EPC will need to be issued upon completion of the dwelling.


Gladwood are able to carry out these assessments and provide cost effective solutions to achieve the pass you require, please contact us for and we will do our best to help you.


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