Back in July 2013 the Department of Communities and Local Government (DCLG) – the agency responsible for Building Regulations in England – announced it was delaying the implementation of Part L 2013 until April 2014. It also announced that it would be setting a target 6% higher than the 2010 Part L standards.

The new requirements will see a major change in the way the National Calculation Methodology (NCM) works for new homes with the introduction of additional targets. These are the Dwelling Fabric Energy Efficiency Standards (DFEES) and the Target Fabric Energy Efficiency Standards (TFEES). The inclusion of these Fabric Energy Efficiency Standards in the new Part L, represents a strong indicator of how the ‘fabric first’ approach to compliance with be used on the road towards the zero carbon targets in 2016.

There is also a change to the way the Target Emissions Rate is produced, and it has been completely redesigned from scratch for 2013. DCLG are referring to this new method as the ‘elemental recipe’. The system seeks to make it easier to understand how to comply. In fact, you can now show compliance just by building to this elemental recipe, although you will still be expected to submit the Standard Assessment Procedure (SAP) calculation to your chosen Building Control.

New Standards

The new system uses limiting U values based on a new recipe of U values, being:

  • 0.13 for floors
  • 0.18 for walls
  • 0.13 for roofs
  • 1.40 for windows, external doors and rooflights
  • You also need to set the air permeability to five, use System 1 ventilation and assume 89.5% efficient mains gas combi heating.
  • This is a huge step up from the 2010 requirements and in practice would be very difficult to achieve. A U value of 0.18 for walls equates to around 180mm of mineral wool in a brick/cavity/block wall for example. But fortunately, this isn’t the whole story as the compliance modelling software will still allow your to flex the design.

Flexing the Design

The backstop values for flexing remain effectively unchanged from the 2010 edition. This means U values of:

  • 0.25 for floors
  • 0.30 for walls
  • 0.00 for party walls
  • 0.20 for roofs
  • 2.00 for windows, rooflights and external doors

Air permeability remains at 10.

Therefore you can play around with the software model to find the most effective flexing for your project as long as your don’t drop below the backstop values and do not exceed the DFEE.

Approaches to Part L

The launch also demonstrated examples of flexing for detached and end terrace properties (as shown in the table below). The first option to include triple glazing resulted in slightly relaxed requirements for walls and floors from the elemental recipe. In the second option, waste water heat recovery (WWHR) means more significant relaxations in walls and roof requirements.

The following table shows two example routes to meet the TER and TFEE for an end terrace property of 76m² — one making use of triple glazing and the other using WWHR.

Appendix R Elemental Recipe End Terrace Triple Glazing End Terrace Relaxed Fabric
External walls (W/m²K) 0.18 0.22 0.26
Party walls (W/m²K) 0 0 0
Floor (W/m²K) 0.13 0.16 0.19
Roof (W/m²K) 0.13 0.13 0.13
Windows (W/m²K) 1.40 0.09 (g=0.57) 1.40
Airtightness (m³/hr.m²) 5 5 5
Gas boiler 89.5% (SEDBUK) 89.5% (SEDBUK) 89.5% (SEDBUK)
Services WWHR
TER (kgCO?/m².yr) 18.72 18.72
DER (kgCO?/m².yr) 18.68 18.67
TFEE (kWh/m².yr) 54.26 54.26
DFEE (kgCO?/m².yr) 46.73 54.20

The changes come into effect in April 2014, but if you are building before April 2015 you can still get away with complying with the 2010 version, as long as you registered with Building Control before April 2014.

Our Sponsors