Conversions & Extensions to Existing Buildings


Energy Calculations Limited can provide calculations required for conversions such as a single dwelling to multiple dwellings, commercial property to domestic property and conversion of an office to flats resulting in a material change of use showing compliance with L1B Building Regulations.

Maximum U-Values are required when renovating or retaining thermal elements as part of a material change of use or material alteration. Altering a house to flats or barn conversion requires this calculation. We will advise on the best method to show compliance with L1B.

The U-Value is an important concept in building design. It represents the air-to-air transmittance of an element. This refers to how well an element resists heat loss. There are limiting U-Values required to show compliance with L1B Building Regulations. The lower U-Value achieved the better.


If a proposed extension has more than 25% glazing of the floor area and is not thermally separate from the main building, the extension will require a SAP report. Minimum U-Values are required for each new element.

The calculations are required to show compliance with L1B Building Regulations. The dwelling is required to show that the CO2 emissions with the proposed extension, is no greater than the dwelling with a notional extension built to the standards required in the approved document.

Please do not hesitate to contact us should you require advice or assistance.

SAP Accreditation Code for Sustainable Homes Elmhurst Accredited Stroma