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Conversions or Extensions

We specialise in SBEM calculations and/or EPCs recommendations for any type of work under Part L2B (commercial properties).

Extension greater than 100m2

Any commercial extension of more than 100sqm with a floor area greater than 25% of the existing building needs to have a design SBEM issued as part of the Building Regulation compliance. Effectively this means that the design of the extension has to meet New-build standards; there may also be a requirement to upgrade the existing building up to 10% of the build costs of the extension.

Extension less than 100m2

The design of the building must be in compliance with Approved Document L2B, which relates to the minimum performance of different elements i.e. u-values for the roof, walls, floors, windows, doors, etc, fixed appliances and fittings and also limits the amount of glazing that can be used. If the area of glazing is increased beyond the threshold, either an SBEM or Area Weighted calculation will be required to prove compliance at design stage.

Energy performance relating to works and extensions in existing buildings is based on a revised elemental approach in which insulation and efficiency thresholds are set for individual parts of the building envelope and services.

Part L2B provides guidance on the standards to be achieved for ‘Thermal Elements’ (walls, floors and roofs), ‘Controlled Fittings’ (windows, doors and similar fittings) and ‘Controlled Services’ (heating, hot water, ventilation systems and lighting), or changing a buildings energy status.  However we can guide you through the whole process.

Approved Document Part L2B

Heating not extended

Exemption from the energy efficiency provisions to extensions consisting of a conservatory or porch has now been amended to grant exemption only where the existing walls, windows, or doors are retained or replaced if removed and where the building’s heating system is NOT extended into the conservatory or porch.

Design Flexibility

  • When constructing an extension you could use an average u-value across the extension's thermal envelope that is the same as if the prescribed u-values had been used for each individual element.  This means that a better value in the walls can be used to trade off against a worse u-value in the roof. 
  • Area weighted u-value of all the extension(s) elements is to be no greater than that of an extension of the same size / shape that complies with the new u-value standards and glazing area restrictions.
  • A further alternative is to use Simplified Building Energy Model (SBEM) calculation tool; to show that the building and extension(s) calculated CO2 emissions is no greater than for the building plus a notional extension complying with the new thermal standards.
  • Where the building is over 1,000m² - the building used for calculation of both the actual and notional extension should incorporate any improvements required by ‘Consequential Improvement’.

Where L2B is not acceptable

There are certain circumstances where for larger extensions this approach is not acceptable and, as such, have to be treated as if they are a new build (L2A). If your extension has a total useful floor area greater than 100m² and greater than 25% of the ‘total useful floor area’ of the existing building then the works are to be treated as a new building and must fully comply with Part L2A. Also, for the first fit-out works such as shell and core buildings, office buildings or business parks the guidance in Part L2A should be followed.

New Extension Linked to Existing Building

Erecting a separate unit on a site with an existing building(s) is not extending that existing building, but the creation of a new building unless the new unit is permanently linked to the existing building.

Consequential Improvements

Where an existing building has a ‘total useful floor area’ over 1,000m² and you intend to carry out any of the following building works:

  • Building an extension
  • The initial provisions of any ‘fixed building services’ (other than renewable energy generator)
  • An increase to the installed capacity of any ‘fixed building services’ (other than a renewable energy generator).

You must bring the existing as well as the new building into compliance with Part L, unless you can prove that such works to the existing building are not technically, functionally or economically feasible. Such supporting evidence must be prepared by a suitably qualified person and provided on application submission.

Will the Extension have to be Air Tested?

Only if the extension is over 100sqm and more than 25% of the existing floor area, or where a design SBEM has been calculated.

EPC required once the extension is complete

An EPC will need to be issued.  Where an extension can be split from the existing building (i.e. has its own heating system) an EPC can be issued for the extension alone, otherwise the whole extended building will need to be assessed and an EPC issued.

We can provide all the compliance documents required by Building Control on any type of project.