This module explains the key changes to the energy efficiency provisions of the Building Regulations, which come into force in April. It is sponsored by Celotex

How to take this module

The free continuing professional development distance learning programme from Building is open to anyone who wants to develop and improve their professional knowledge. These modules can contribute towards annual CPD activity and help you to maintain membership of professional institutions and bodies.

To take this module, read the technical article above and click through to the multiple-choice questionnaire.

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Once taken you will receive your results and if you successfully pass you will be automatically issued with a certificate to print for your records. This module will contribute one hour towards your CPD obligations.

DEADLINE: 11 APRIL 2014.

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Introduction

The 2013 revision to Part L of the Building Regulations is a key milestone towards the government’s target for all new homes to be zero-carbon by 2016, and new non-domestic buildings by 2019. Following a long consultation period, new carbon emission targets were published in November 2013. These set a 6% improvement on the 2010 Part L targets for housing on aggregate - which means there may be flexibility across different types of homes - and a 9% improvement on aggregate for non-housing. As the industry gears up for the introduction of the revised Part L on 6 April 2014, this CPD sets out to explain the method behind it, and show how it can be implemented.

Changes to Part L1A for new dwellings

  • The TFEE Previous versions of Part L only required the designer to hit a target emission rate (TER) for carbon dioxide (CO2). In Approved Document L 2013 there is now a second standard called the fabric energy efficiency standard (FEES), for which a target fabric energy efficiency (TFEE) is set. This focuses on the energy demand of the building, and will therefore drive efficiency through measures that reduce energy use - such as a “fabric first” approach - rather than mitigating CO2 through building systems and renewable technologies. The TFEE is measured in kWh/m2/yr and is therefore not affected by the relative carbon emissions of different fuel types.

The key factors that influence a building’s fabric energy efficiency are:

  • U-values of floors, walls and roofs
  • U-values of windows and doors
  • Thermal bridging
  • Air permeability
  • Thermal mass
  • External heat gain (solar gain)
  • Internal heat gains

The TFEE is calculated by determining the fabric energy efficiency from a notional dwelling of the same size and shape as the actual dwelling. This value is then increased by 15% to give the TFEE.

  • New notional dwelling There is a new notional domestic building for Part L1A 2013, replacing the 2002 version used previously. The specifications for the notional home are published for the first time within the Part L document itself in Section 5: Model Designs. Some of the key values include:
Element or systemValue
External walls0.18W/m2K
Party walls0.0W/m2K
Floor0.13W/m2K
Roof0.13W/m2K
Windows, roof windows, glazed rooflights and glazed doors1.4W/m2K
Opaque doors1.0W/m2K
Semi-glazed doors1.2W/m2K
Airtightness5.0m3/hr/m2
  • Limiting fabric U-values The limiting fabric U-values remain unchanged from those in Part L 2010 and are shown below.

Limiting U-value (W/m2K)
Wall0.30
Party wall0.20
Floor0.25
Roof0.20
Windows2.00

How to comply

  • Notional or limiting U-values? Part L1A 2013 allows flexibility in design, so that elements of the building can be varied according to requirements, as long as overall targets for CO2 and energy are met, and the limiting fabric U-values are not exceeded. This is referred to as the “elemental recipe” approach.
    Part L1A 2013 states that “to achieve the TER and the TFEE rate, a significantly better fabric performance than that set out in Table 2 (limiting fabric U-values) is likely to be required’. So designers are best advised to start not from the limiting fabric U-values, but from the notional building U-values in Section 5: Model Designs.
  • Thermal bridging Thermal bridging must be addressed to give the best chance of compliance. If no attention is paid to thermal bridging and the default value of y = 0.15 is taken, it will be very difficult to compensate elsewhere in the design.
  • Party walls If the dwelling has a party wall, the best course of action is to ensure that it is either of solid design or is fully filled and sealed. Both of these approaches will enable a U-value of 0 to be used. Failure to do this will require further measures elsewhere in the design to compensate for the increase in CO2, and will make compliance more difficult
  • Flexing the fabric The table below shows an example of how the ingredients of the elemental recipe can be adjusted, or “flexed”, when triple glazing is added to a 76m2 end-of-terrace home.
 Elemental recipeTriple glazing
Wall (W/m2K)0.180.22
Party wall (W/m2K)00
Floor (W/m2K)0.130.16
Roof (W/m2K)0.130.13
Windows (W/m2K)1.40.09
Airtightness (W/m2K)55
Gas boiler efficiency89.5%89.5%
TER (kgCO2/m2/yr)18.7218.72
DER (kgCO2/m2/yr)18.7218.68
TFEE (kWh/m2/yr)54.2654.26
DFEE (kWh/m2/yr)47.1846.73

In the elemental recipe column, the DFEE represents the energy use of the notional dwelling; the TFEE is this figure multiplied by 1.15. The second column shows that by introducing higher performance glazing into the recipe, the walls and floor can be allowed slightly higher U-values without adversely affecting the DER or DFEE.

  • Aggregate approach The 6% domestic target is an aggregate figure across the mix of housing types. Those dwellings with the most fabric, such as detached properties, must achieve greater emissions reductions than those with less fabric and therefore less scope for improvement, such as a mid-floor flat.

Celotex PIR insulation was used to line the concrete walls and floors of the Hepworth Wakefield to help the gallery achieve very low U-values

Celotex PIR insulation was used to line the concrete walls and floors of the Hepworth Wakefield to help the gallery achieve very low U-values

Changes for existing homes

Part L 2013 makes no changes to the U-values required when making home improvements. The maximum values are shown in the table below:


New thermal element (W/m2K)Upgrade to existing element (W/m2K)
Floors0.220.25
Walls0.280.30
Roofs0.180.18

Changes to Part L2A for new non-domestic buildings

Commercial and other non-domestic buildings will not be expected to meet the requirements for FEES, and therefore the SBEM approach is not noticeably different from 2010. The main change is the 9% aggregate increase on the TER, and the fact that greater variation is included between building types, as shown below:

Distribution warehouse4%
Deep-plan office with air-conditioning12%
Retail warehouse8%
Shallow-plan office13%
Hotel12%
School9%
Small warehouse3%
Aggregate across build mix9%

Another change is that there is a wider set of notional buildings used to determine CO2 targets. The three building types are:

  • Side-lit or unlit, heating only (SLU-H)
  • Side-lit or unlit, includes cooling (SLU-C)
  • Top-lit.

Limiting U-values are unchanged from 2010, regardless of the notional building type. These are: 0.26W/m2K for walls, 0.22W/m2K for floors, 0.18W/m2K for roofs and 1.6W/m2K for windows (although this does not apply to top-lit buildings).

However, there is variation in the notional buildings’ air permeability, which have been subdivided by size. This is because the larger the building, the easier it is to achieve airtightness. The new values are as follows:

 SLU-H (m3/hr/m2)SLU-C (m3/hr/m2)Top-lit (m3/hr/m2)
0-249m2557
250-3,499m2337
3,500-9,999m2335
10,000m2 +333


A summary of the Part L2A notional buildings is published in Section 5: Model Designs of the Approved Document. If the actual building is constructed to the notional specifications it will meet the CO2 targets and the limiting fabric and building services parameters. However, developers are free to vary the specification, provided the same overall level of CO2 emissions is achieved or bettered.

How to take this module

The free continuing professional development distance learning programme from Building is open to anyone who wants to develop and improve their professional knowledge. These modules can contribute towards annual CPD activity and help you to maintain membership of professional institutions and bodies.

To take this module, read the technical article above and click through to the multiple-choice questionnaire.

Celotex-Logo

Once taken you will receive your results and if you successfully pass you will be automatically issued with a certificate to print for your records. This module will contribute one hour towards your CPD obligations.

DEADLINE: 11 APRIL 2014.

CPD Button

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