Our energy expert runs through the parts of the new rules that will have the biggest impact

The Approved Documents for Part L of the Building Regulations were published today - what are the big changes that will affect builders and designers of domestic properties?

1) 25% less CO2 emissions that in 2006Part L1A 2010 - for new dwellings - aims to reduce CO2 emissions by 25% over Part L1A 2006. This is a 40% improvement over a dwelling built to the 2002 regulations and corresponds roughly with the trigger point for Code for Sustainable Homes Level 3, in line with the government’s strategy for getting newbuild dwellings to zero carbon by 2016.

2) The ’Flat’ TER wins the dayThe Target Emission Rate (TER) is calculated in much the same way as it was in Part L1A 2006. The main differences are that (a) an improvement factor of 0.4 is used rather than 0.2 to give the 40% improvement referred to above and (b) the SAP 2009 methodology is used to estimate the carbon emissions from heating, hot water, lighting, pumps and fans. The fuel factors have not changed so that electric heat pumps and biomass will continue to be encouraged by the TER; although this is countered to an extent by lower limiting U-values (see point 8 below). The fuel factor for heat pumps is also to be reviewed after the renewable heat incentive is introduced next year. The ’Aggregate’ TER for dwellings was rejected on the grounds that the benefits did not justify a change in methodology at this stage, despite the aggregate option being selected for non domestic dwellings. he issue will be re-examined for Part L1A 2013. You can explore how to meet the new TER in practice using the updated NHER SAP 2009 Preview software: http://www.nesltd.co.uk/content/sap-2009-preview

3) Cavity party walls - insulating and sealing them does not count towards the 25% reductionA key feature of SAP 2009 is that party walls with unfilled and unsealed cavities are assumed to have a U value of 0.5W/m2K. The notional dwelling used in calculating the TER assumes a U-value for cavity party walls of 0.0W/m2K. This compares to 0.4 W/m2K in last year’s Part L1A 2010 consultation. This means that insulating and sealing cavity party walls will not count towards the 25% improvement target.

4) Thermal bridges - 0.08 for accredited construction details is no longer an optionIn Part L1A 2006, it is acceptable to assume an effective U-value (the y value) of 0.08W/m2K if accredited construction details have been used. This will not be possible with Part L1A 2010. Instead, the length of each junction will need to be measured, multiplied by the appropriate psi values and added up to produce the y value. The psi values can either be values already supplied in the SAP 2009 document or supplied by the relevant approved government accredited construction detail scheme. The psi values can also be calculated for specific junctions. A confidence factor will be applied to the psi value calculation for an individual junction if either (a) the calculated psi values are not from a government approved accredited details scheme or (b) if no on site checks can be demonstrated to have been made. The confidence factor applied to the psi value calculation is 25% or 0.02, whichever is the larger.

5) Air Permeability - more pressure testing and a confidence factor for untested dwellingsThe volume of pressure testing required will roughly double. A pressure test should be carried out on three units of each dwelling type or 50% of the instances of the dwelling type, whichever is the smaller.

In addition, a confidence factor will apply to dwellings not pressure tested. Where a dwelling has been pressure tested, the measured value is used in the calculation of the dwelling emissions rate (DER). Where the dwelling has not been pressure tested, the value used in the DER calculation is the average of the measured values for dwellings of the same type but with the addition of a confidence factor of 2.0 m3/(hm2) at 50 pa. This means in effect that the design air permeability must be at most 8.0m3/(hm2) in order to meet the maximum allowable value of 10.0m3/(hm2) at completion of the dwelling. A value of 15.0m3/(hm2) can still be used in small developments.

6) Low energy lighting - 100% counts towards meeting the target emissions rateA minimum of 75% of light fittings must be low energy. If further low energy light fittings are also low energy, the full 100% will contribute towards meeting the target emissions rate (TER).

7) Electric secondary heating - no longer assumedIn Part L 2006, a penalty was applied in dwellings not fitted with a secondary heating appliance. In such cases it was assumed that 10% of the heat in the property came from direct acting electric heaters, thereby significantly increasing the dwelling emission rate. In Part L 2010, there is no such penalty unless the dwelling has a chimney or flue and no appliance is installed; in such cases the calculation is the same as in 2006.

8) New limiting U-values - including for party wallsElement 2006 2010

Roof 0.25 0.20

External wall 0.35 0.30

Party wall N/A 0.20

Floor 0.25 0.25

Windows 2.20 2.00

Air permeability 10 10

9) ’Design’ submissions now part of regulation - alongside ’as built’ submissionsIn Part L1A 2006, it was recommended that a submission be provided to building control prior to the building work being completed on site; but this not an absolute requirement. However, in Part L1A 2010 the person carrying out the work must provide building control the target emission rate (TER), dwelling emission rate (DER) and a list of specifications before work starts on site. Then, no later than five days after the work has been completed, they must notify building control of the TER and DER actually achieved, and whether the building has been constructed as per the design specification; if not, a list of changes to the design specification must be supplied. This is to better enable building control to confirm that what has been built aligns with the claimed performance. New outputs from SAP software will be available to help building control with this process.

10) Addressing the performance gapThere is growing evidence that completed dwellings do not in practice achieve the intended energy performance. This is referred to by government as the ’performance gap’. If we are to achieve true zero carbon by 2016 it is vital that this gap be closed. Part L1A 2010 contains various things that aim to contribute to this. Firstly, the document is clearer than previous versions in distinguishing between ’Regulation’ and ’Guidance’ and is less ambiguous in many places. This should help developers better understand what is required of them and give building control clearer guidance on how to check for compliance. Secondly, the requirement to produce a ’design submission’ as well as an ’as built submission’, including a comparison of specifications, will hopefully bring more standardisation and rigour to the compliance checks. Thirdly, the notion of ’confidence factors’ should start to reward those developers who adopt good quality control procedures both in design and on site. We can expect to see more of these confidence factors in 2013 and beyond.