Changes to Building Regulations - Part L1A 2010
Part L1A of the Building Regulations came into force in October 2010. This is quite a change from the current Part L1A regime, and it is strongly recommended that architects, developers and contractors are aware of the main changes from Part L1A 2006, as all will have a role to play in ensuring compliance.
- 25% reduction in CO2 emissions from that in 2006 Regulations
- Cavity Party Walls - insulating / sealing them now a requirement
- Non-repeating Thermal Bridges - more stringent assessment method
- Air Permeability - more pressure testing and a confidence factor for untested dwellings
- Low Energy Lighting - 100% counts towards meeting the TER
- New Limiting U-values - including party walls
- 'Design' Submissions now part of Regulation - alongside 'As Built' Submissions
- Addressing the Performance Gap
Further Information
1. 25% reduction in CO2 emissions from that in 2006 Regulations
Part L1A 2010 aims to reduce CO2 emissions by 25% over Part L1A 2006. This is a 40% improvement over a dwelling built to the 2002 regulations. This corresponds roughly with the trigger point for Code for Sustainable Homes Level 3, in line with the government's strategy for getting new-build dwellings to zero carbon by 2016.
This uplift is going to see dwellings require improved fabric U-values, improved approaches to thermal bridging, greater air-tightness, improved heating & ventilation specifications and in many cases increased use of renewable and low carbon technologies.
2. Cavity Party Walls - insulating / sealing them now a requirement
A key feature of the revised calculation methodology (SAP 2009) for Building Regulations is that party walls with unfilled and unsealed cavities are assumed to have a U-value of 0.5 W/m²K. Where dwellings feature this type of construction, it can be an important step in the compliance process to ensure these walls are at least sealed, or preferably fully filled.
Particular attention will need to be given to this issue to ensure no conflicts with the requirements to provide sound attenuation if seeking Code for Sustainable Homes points for sound insulation.
3. Non-repeating Thermal Bridges - more stringent assessment method
Under the current Part L1A (2006), it is acceptable to assume a single y value of 0.08 W/m²K for non-repeating thermal bridges if Accredited Construction Details (ACD) 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 an 'effective' y value. This will normally be the job of the SAP assessor and will involve more time.
The psi values can either be values already supplied in the SAP 2009 document or supplied by the relevant approved government ACD 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.
4. Air Permeability - more pressure testing and a confidence factor for untested dwellings
The 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 Emission 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/(h.m²) at 50pa.
This means in effect that the design air permeability must be at most 8.0 in order to meet the maximum allowable value of 10.0 at completion of the dwelling. A value of 15.0 can still be used in single or two unit developments.
5. Low Energy Lighting - 100% counts towards meeting the TER
A minimum of 75% of light fittings must be low energy, but these do not have to have dedicated fittings. If further low energy light fittings are also low energy, the full 100% will contribute towards meeting the Target Emission Rate (TER) target for the dwelling. Therefore, specifying low energy lighting throughout a dwelling will be a positive step in securing compliance.
6. New Limiting U-values - including party walls
Limiting U-values have been revised, with changes to external wall, roof and window values and the inclusion of a limiting value for party walls. These are summarised in the table below -
| Element |
2006 |
2010 |
| Roof |
0.25 |
0.2 |
| External Wall |
0.35 |
0.3 |
| Party Wall |
n/a |
0.2 |
| Floor |
0.25 |
0.25 |
| Windows |
2.20 |
2.00 |
| Air permeability |
10 |
10 |
7. 'Design' Submissions now part of Regulation - alongside 'As Built' Submissions
In 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 was not an absolute requirement.
However, in Part L1A 2010 the person carrying out the work must provide building control the TER, DER and a list of specifications before work starts on site. Then, no later than 5 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.
8. Addressing the Performance Gap
There 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 Stage' 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.
Further Information
Approved Document ADL1A 2010 can be found here: http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1A_2010.pdf
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