CPD articles

CPD: Part L 2013

3 January 2014

• Summary of the new changes
• What they mean for construction
• What you need to do if work has started already

Click here to be taken to the online CPD test paper for January 2014

Part L of the Building Regulations is set to change in April 2014. Geoff Wilkinson looks at the key elements that will affect designers and construction managers.

After months of delay and speculation the Department for Communities and Local Government finally released the new Part L Approved Documents in November. The new standards won’t apply until April 2014, however, giving contractors and designers time to adjust to the changes or apply for approval in advance (see Transitional provisions box).

DCLG considers the changes to be a significant “technical” step that strikes a balance between zero carbon and growth commitments within the economy. The DCLG confirmed that it remains committed to zero carbon in 2016 and is consulting on design principles and options for allowable solutions which will form the basis of the next step.

Part L1a: New housing

The most important changes take place in Approved Document L1a, which applies to new housing. Here we see an average headline improvement 6% higher than the current (2010) Part L standards – substantially lower than the 25% adjustment originally planned. But don’t be taken in by that, as depending on house type this average increase may vary significantly, with detached buildings being more complex to make compliant than terraced ones.

The new requirements also herald a major change in the way the National Calculation Methodology works for new dwellings, with the introduction of additional targets. These are the Dwelling Fabric Energy Efficiency Standards (DFEES) and the Target Fabric Energy Efficiency Standards (TFEES) – Duffys and Tuffys for lovers of neologisms.

The introduction of Fabric Energy Efficiency Standards (FEES) recognises that developers had been continuing to build poor performing leaky buildings and offsetting that by adding “eco bling”. FEES represents a strong indicator that DCLG wants developers to adopt a fabric first approach to compliance, and we can expect this to be reinforced further in the 2016 zero carbon targets.

It doesn’t stop there either, as there is also a change to the way the target emission rate (TER) is produced, as instead of updating the 2001 specification to create the target (as has previously been the case), the specification has been completely redesigned for 2013. DCLG is referring to this new method as the “elemental recipe”, which is intended to create a simple and easy to follow route to compliance for the novice and self build market.

By following the elemental recipe (see Table 1 below) you can be sure that you will meet Part L requirements, although you will still be expected to submit the Standard Assessment Procedure (SAP) calculation to your chosen building control body.

Element or system
Required value or specification
Opening areas (windows and doors)
Same as actual dwelling up to a maximum proportion of 25% of total floor area
External walls (including opaque elements of curtain walls)
Party walls
Floor 0.13W/m2K
Roof 0.13W/m2K
Windows, roof windows, glazed rooflights and glazed doors 1.4W/m2K (whole window U-value g value = 0.63
Opaque doors 1.0W/m2K
Semi glazed doors 1.2W/m2K
Air tightness 5.0W/m2K
Linear thermal transmittance Standardised psi values – except use of y = 0.05W/m2K if the default value of y = 0.05W/m2K is used in the actual dwelling
Ventilation Natural (with extract fans)
Air conditioning None
Heating system

Mains gas.
If combi boiler in actual dwelling, combi boiler, otherwise regular boiler
Room sealed
Fan flue
SEDBUK 2009 89.5% efficient

Controls Time and temperature zone control
Weather compensation
Modulating boiler with interlock
Hot water storage system Heated by boiler (regular or combi as above)
If cylinder specified in actual dwelling, volume of cylinder in actual dwelling
If combi boiler no cylinder, otherwise 150 litres
Located in heat space
Thermostat controlled
Separate time control for space and water heating
Primary pipework Fully insulated
Hot water cylinder loss factor (if specified) Declared loss factor equal or better than 0.85 x (0.2 x 0.051 V2/3) kWh/day
Secondary space heating None
Low energy lighting 100% low energy lighting
Thermal mass parameter Medium (TMP = 250)

Table 1: Concurrent notional dwelling specifications to meet Part L for housing

This is not entirely a new concept having been used in Scotland for a few years, and reflects criticism in the Lakanal House report following the April 2013 Lakanal House inquiry that the Approved Documents are too difficult for the lay person to follow. Indeed, the new approved document follows the new DCLG house style which is easier to understand and adopts a single column layout making it easier to view on tablets and mobile devices.

As you will see, Table 1 assumes new homes will be constructed to the new “recipe” of U-values: 0.13 for floors, 0.18 for walls, 0.00 for party walls, 0.13 for roofs and 1.40 for windows, external doors and rooflights. You also need to set the air permeability to five, use “natural” or System 1 ventilation (background ventilators and intermittent extract fans) and assume 89.5% efficient mains gas combi heating.

This is a huge step up from the 2010 requirements and would be very difficult to achieve in practice – a U-value of 0.18 for walls equates to around 180mm of mineral wool in a traditional brick/cavity/block wall, for example. Fortunately, the SAP software will still allow the design to be flexed.

You will be pleased to hear that the maximum allowable “backstop” values for flexing remain effectively unchanged from the 2010 edition, meaning U-values of 0.25 for floors, 0.30 for walls, 0.00 for party walls, 0.20 for roofs and 2.00 for windows, roof-lights and external doors. Air permeability also remains at 10. Therefore you can play around with the software model to find the most effective flexing for your project, so long as you don’t drop below the backstop values, and do not exceed the DFEE.

As an example of flexing, two options for an end terrace property are shown below in Table 2. The first column shows the baseline elemental recipe approach option. The second column shows the effect of flexing the fabric against fabric – that is, dropping the walls and floor but upgrading the glazing.

Elemental recipe
Triple glazing Relaxed fabric
External walls (W/m2K)
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
1.4  0.09 (g=0.57)
Air tightness (m3/hr.m2)
 5 5
Gas bolier
89.5% (SEDBUK)
 89.5% (SEDBUK)  89.5% (SEDBUK)

 -  WWHR
TER (kgCO2/m2.yr)

 18.72  18.72
DER (kgCO2/m2.yr)    18.68  18.67
TFEE (kWh/m2.yr)

 54.26  54.26
DFEE (kWh/m2.yr)
 46.73 54.20

Table 2: Example routes to meet the TER and TFEE - end terrace house 76m2

The third column shows the effect of flexing the fabric against services – in this case waste water heat recovery (WWHR). You will note that the dwelling emission rate (DER) v TER is consistent in both cases while the TFEE v DFEE is not. In the second column, where we are flexing fabric against fabric, the TFEE v DFEE calculation sails through, whereas trying to flex fabric against services results in a DFEE that is only just below the TFEE.

It should also be pointed out that the DFEE is bespoke to the dwelling plot being considered, and thermal bridges should be calculated on the length of the actual bridge and psi values (measuring heat loss) in each case rather than simply by default values. Adopting the default values would result in very significant penalties, in overall compliance.

In fact, thermal bridging is one of the major challenges for the DCLG as it seeks to close the gap between design performance and as-built performance on building sites. This will lead to ever greater emphasis on construction joint detailing, and use of offsite fabrication and accredited construction details.

The new SAP software isn’t available yet, and will only be available in a beta version until the commercial software companies release their updates.

Part L2a: New non-domestic buildings

Outside of new dwellings the changes are less far reaching as commercial buildings will not be expected to meet the requirements for Fabric Energy Efficiency Standards (FEES). As a result the Simplified Building Energy Model (SBEM) approach is not noticeably different from 2010, apart from the average 9% uplift previously announced. Again, it should be pointed out that the 9% varies by building type with the uplift for warehousing only increasing by around 6%, while offices bear the brunt of the uplift at around 12% (see Table 3).

Warehouse (distribution)
Office (deep plan, AC)
Warehouse (retail)
Office (shallow plan, AC)
Hotal (5-star)

Table 3: Improvements over Part L 2010

The new notional buildings are now classed as either side lit (with or without cooling) or top lit, and air permeability is based upon gross internal floor area. There are minor changes to the way that lighting is treated to penalise over-lit spaces, and an alternate calculation methodology called Lighting Energy Numeric Indicator (or LENI) has been introduced. There are also minor changes to the way that district heating systems are considered, resulting in additional benefits from adopting such systems.

L2 A&B: Existing buildings

Changes here are nominal and DCLG is at pains to explain that it considers regulation as a last resort in addressing market failure and claims much has already been done through previous Part L amendments to strengthen energy efficiency standards to existing properties.

While there was support for strengthening domestic extension standards, the consultation stage impact assessment showed that the present value of revenues from energy savings, was insufficient on its own to cover the present value of costs.

In particular, proposals for extending the requirements for consequential improvements raised a number of concerns about deterring home owners from carrying out building works, thus stifling growth. For these and other reasons, including the associated inconsistency with reforms to the need to obtain planning permission, it has been decided not to proceed with changes for existing homes.

To help maintain consistency of construction standards it has also been decided not to proceed with the introduction of a separate set of strengthened standards for the extension of non-domestic buildings that are domestic in character.

The main changes to L2 have therefore been in the Building Services Compliance Guide standards for the replacement of fixed building services such as minimum cooling efficiency increases for chillers, tighter standards for fan coil units and increased initial luminaire efficacy to 60 lamp lumens per circuit watt.

These changes to the standards for replacement services to existing buildings will come into force from 6 April, subject to appropriate transitional provisions.

Transitional provisions

DCLG has confirmed the transitional provisions for Part L as follows:

DCLG has also clarified its definition of commencement of work as:

Therefore the following sorts of work would not constitute the commencement of work:

In some cases applications will be in respect of a number of buildings on a site, for example a number of houses. In such cases it is the commencement of work on the first of the buildings within the application which determines whether all the building work can take advantage of the transitional provisions, not each individual building.

We would advise that projects that are currently being designed to the current 2010 requirements should be submitted at least five working days prior to 6 April 2014 and ensure you notify the building inspector to undertake a site visit prior to 5 April 2015. If this is not possible then you should be aware of the potential increase costs involved with the new regulations and need for redesign to the new standards.

Geoff Wilkinson is managing director of approved inspectors Wilkinson Construction Consultants and vice chair of the CIOB Building Control & Standards Faculty

Click here to be taken to the online CPD test paper for January 2014


With regard to transitional provisions a buiding regulations application or initial notice may be submitted before 6th April 2014 which will allow the proposals to comply with 2010 part L subject to work commencing prior to April 2015

Anthony Taylor, 15 January 2014

I found the information very informative, please send CPD articles and questions to my email to further my learning if this is a service you offer.

Sam burton, 29 January 2014

An interesting review, its a shame that the tweaking will still not stop the clients opening windows, and the incorporation of solar pv still makes a huge difference and should be compulsory.

Barrie Spark, 30 January 2014

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