Part L the approved document setting out guidelines for the conservation of fuel and power has been revised and a new edition goes live on 6th April 2014.

Amongst the changes include the introduction of:

  • 6% aggregate reduction of CO₂emissions
  • A new compulsory target based on the energy efficiency of the building fabric (FEES).  FEES sets a maximum limit on the amount of energy normally required to ensure a comfortable internal temperature in the home.
  • A new notional building to replace the existing first introduced in 2002. The new notional building promotes a strong fabric performance and sets out domestic targets for various elements linked to the building envelope. The domestic targets will for some allow consistency of specification across building types.

So as the 6th of April fast approaches what do these changes really mean and how do they affect new projects in the pipeline?

What does the 6th April actually mean?

If plans for your project have been submitted to Building Control or a Local Authority before 6th April, compliance to Part L 2013 will not apply. This is providing work has commenced on site before 6th April. This is what’s known as ‘The Transitional Arrangement’. The changes to Part L 2013 will only apply to plans submitted after 6th April 2014.

When should a SAP calculation be carried out?

Simply put, a SAP calculation is required to demonstrate a dwellings’ compliance of CO₂ emissions (TER) and Energy Consumption (TFEES) to Part L 2013.  SAP is a desktop exercise and is applied to the project both at design stage and at the final ‘as built’ stage.  A completed SAP calculation creates an Energy Performance Certificate based on the dwelling as built and is required to be displayed in a new dwelling put up for sale or rent on the open market.

It is favourable to introduce a SAP calculation at the earliest design stages. This allows the Architect to make changes to the design if at first it does not comply to the TER and TFEES required within the notional building.

If the SAP is first performed later on in the design process, perhaps by the contractor, and it fails to hit the required targets, it will be more difficult to alter elements affecting the fabric performance. For example, changing the width of a wall or altering the depth of rafters.

Have you got any handy hints to help comply with the new Regulations?

The new notional building and the introduction of a target for energy consumption points to adopting a ‘fabric first’ approach to compliance. This means ensuring the building envelope complies with key fabric targets and so prevents heat loss and reduces energy demand.


Handy hint no 1: The notional building seeks good U-values through the roof, walls and floors.  It will no longer be possible to achieve compliance using backstop values without the considerable upgrade of other key fabric targets.

Handy hint No 2: There is a new requirement for airtightness within the notional building setting a minimum value of 5m3/(h.m2) @ 50Pa.  This means tightening up on uncontrolled air leakage by correctly finishing and sealing internal linings as well as considering the benefits of air tight barriers.  Anything less than this target will mean the introduction of controlled ventilation.

Handy hint No 3:  Thermal bridging forms a key component to compliance. The junctions between walls with floors and roofs will need to be detailed to a standard better than Accredited Construction Details. In some cases there may be a requirement for the junctions to be modelled by an independent energy assessor in order to achieve compliance.

Handy hint No 4:  Party walls are fully filled and sealed to achieve the 0W/m²K required in the new notional building.

And finally, something to think about…

The changes introduced into Part L 2013 applicable to domestic dwellings are seen as a step towards the Government’s target of zero carbon in 2016.  This has introduced a fabric first approach when designing new domestic dwellings meaning key fabric energy targets are the focus for compliance.  With the 2016 zero carbon target in mind there are some that suggest targets within the new notional building are the minimum standards required especially as Part L consultations led us to expect CO₂ reductions greater than 6% on aggregate.

The key fabric energy targets for the new notional building in Part L1A 2013 is an improvement over Part L1A 2010 but should designers aim to exceed the TER and TFEE? A final SAP calculation of the DER and DFEE rate is required to take into account any changes in performance between design and construction.  It could be that designing to standards better than TER and TFEE not only has a favourable impact on CO2 emissions, it also allows for any last minute changes in design and so ensures building performance while adopting a fabric first approach.

For more information on the UK Building Regulations and to download your Part L Guide, visit the Insulating Britain website.