Part L changes for 2014: here’s how they might affect you

Part L Building Regulations have been updated for 2014. Here’s our primer to keep you up to speed with the changes.

An introduction: what is Part L?

Part L is the section of the Government’s Building Regulations concerning the conservation of fuel and power. All new and rebuilt buildings, whether dwellings or non-dwellings, must comply with the specifications in Part L. This includes targets for insulation values, heating efficiency, hot water storage, air tightness and carbon emissions. It also sets out the requirements for SAP calculations, which result in an Energy Performance Certificate for the building (a mandatory requirement).

Each time Part L is updated, the targets for CO2 emissions become tighter. This means that all of the individual calculations affecting the emissions total must be carefully calibrated, to contribute to the energy efficiency of the whole building.

When was Part L updated?

Consultations for revised CO2 targets took place in 2013. The revised document comes into force on 6th April 2014, and is for use in England. If plans have been submitted for new builds before 6th April 2014, and work begins on site before that date, the 2010 Part L applies instead.

What are the changes?

The main changes from previous Part L regulations, for dwellings, are as follows:

  • Carbon Reductions – now 6% for domestic buildings and 9% for non-domestic buildings.
  • CO2 reduction target is now aggregate across building type – this means that the dwellings with the most fabric, such as detached houses, will be asked to reduce emissions by more than those with less fabric, such as mid-floor flats.
  • FEES, a new target to meet – this stands for Fabric Energy Efficiency Standard, and measures the energy demand of the dwelling.
  • The effects of heat gains in summer are now limited – calculations include heat from pipes, not just solar gains.
  • There is a new Notional Building in SAP, and a recipe approach for compliance – the parameters to follow to achieve compliance are published within Part L Section 5: Model Designs. The Notional Dwelling specifications look like this:
Element or System Values
External Walls 0.18 W/m2K
Party Walls 0.0 W/m2K
Floor 0.13 W/m2K
Roof 0.13 W/m2K
Windows, roof windows, glazed rooflights & glazed doors 1.4 W/m2K

g-value 0.63

Opaque doors 1.0 W/m2K
Semi-glazed doors 1.2 W/m2K
Air-tightness 5.0 m3/hr/m2
Linear Thermal Transmittance 1. If the thermal bridging in the actual dwelling has been specified by using the default y-value of 0.15 W/m²K, the thermal bridging is defined by y = 0.05 W/m²K.

2. Otherwise the thermal bridging allowance is calculated using the lengths of junctions in the actual dwelling and the psi values in Table R2 in of SAP 2012

Ventilation type Natural (with extract fans)
Air conditioning None
Heating system Mains gas, boiler (SEDBUK 2009 89.5% efficient) and radiators
Low energy lighting 100%
Thermal Mass Parameter Medium (TMP=250)

For existing domestic dwellings, target U-values remain unchanged.

The main changes from previous Part L regulations, for non-dwellings, are as follows:

  • 9% aggregate CO2 reduction – buildings with more fabric asked to do more than buildings with less. For example, a small warehouse must reduce CO2 by 3%, whereas the target for a hotel is 12%, and that for a shallow plan office is 13%.
  • There is a wider range of Notional Buildings – Side Lit or unlit (heating only); Side Lit or unlit (includes cooling); Top Lit.
  • Air tightness values vary by Gross Internal Area.

 How can I learn more?

The revised Part L documents can be found here, and can be downloaded. You can find out more about our assessment services on our website.

We’ll be updating our website with new guidelines soon. Until then, you can call or email us with any questions, on 01454317940, or


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