Approved document L


Robert Street Architects can assist with providing provisional guidance on thermal efficiencies and how these can be achieved most economically. We take a fabric first approach to environmental design. Simply put we prefer to keep the heat in as much as possible by increasing levels of insulation and reducing heat loss through cold bridges (where cold structural elements span across the insulation). It is key to remember that Part L sets out national standards however the cost implications of increasing the depth insulation by 20-50mm can vastly reduce heating demand and cost very little extra in material costs. Increasing the level of insulation can have an impact on the internal space. Robert Street Architects can assist in reviewing the opportunities of maximising thermal efficiencies while maintaining a high quality of space within the property.

The Building Regulations set out requirements for specific aspects of building design and construction. Regulation 26 of the building regulations states that “Where a building is erected, it shall not exceed the target CO2 emission rate for the building…”, and Schedule 1 – Part L Conservation of fuel and power states that provision for conservation of fuel and power shall be made by: limiting heat gain and losses and providing building service which are efficient, have effective controls and are properly commissioned and that information is provided so that the building can be operated efficiently.

Approved documents

A series of approved documents provide general guidance on how different aspects of building design and construction can comply with the Building Regulations. Approved Document L: Conservation of fuel and power, deals with energy efficiency requirements.

There are four parts to Approved Document L:

  • Approved Document L1A: Conservation of fuel and power (New dwellings).
  • Approved Document L1B: Conservation of fuel and power (Existing dwellings).
  • Approved Document L2A: Conservation of fuel and power (New buildings other than dwellings).
  • Approved Document L2B: Conservation of fuel and power (Existing buildings other than dwellings).


Key criterion described in Approved Document L include:

  1. The designed carbon emission rate (Dwelling Emission Rate (DER) for self-contained dwellings and individual flats (excluding common areas) and Building Emission Rate (BER) for buildings other than dwellings) must not exceed the Target Emission Rate (TER) for a notional building of similar type, size and shape. Both are expressed in kgCO2/m2 per year.
  2. Fixed building services should achieve a reasonable standard of energy efficiency. This is intended to prevent inappropriate trade-offs between different elements of the building. Minimum limiting parameters are set for key components of the building fabric to ensure that this is the case.
  3. Solar gains should be limited.
  4. As-built performance should be consistent with the DER. This includes air-permeability testing and appropriate commissioning of building services systems.
  5. Provision should be made for energy efficient operation by providing the building owner with information enabling them to operate the building in a way that uses no more fuel and power than is reasonable. This might be done by the preparation of a building log book.
  6. Limiting fabric parameters.

Robert Street Architects can assist with obtaining the required reports and documentation to achieve approval from Building Control. The key however is to understand the requirements of the efficiency standards to design these into a scheme at an early stage so space is not lost at the construction phase compromising the interior design.