Part L: a comprehensive guide to the major changes

Context

In the week that scientists published research in the journal Science indicating that carbon dioxide levels have reached their highest level for over two million years and the UK Climate Impacts Programme (UKCIP) updated their climate projections , the Communities and Local Government Department (CLG) issued a consultation document on the proposed changes to Part L (and F) due in 2010.

It doesn’t seem so long ago that Part L of the Building Regulations was revised; indeed it is only three years. The consultation document is extensive, covering three volumes and is close to 800 pages in total. It sets out the strategic background, the proposed changes to the approved documents, the National Calculation Methodology (NCM), an regulatory impact assessment and the compliance guides.

Although not considered here, the proposed revisions need to be considered in the context of the government’s commitment to an 80% cut in carbon emission iby 2050 and of other consultations such as the Definition of Zero Homes and Non-Domestic Buildings and the Heat and Energy Saving Strategy (HESS).

The revisions shouldn’t come as a surprise. Buildings account, directly and indirectly for, 44% of the UK’s carbon emissions. The Government has long signalled its intention to move to zero carbon buildings, starting with homes in 2016 and finishing with all other buildings by 2019.

Building Regulations Part L has an important role in achieving this goal. Change is always difficult but this set of revisions is more evolutionary than revolutionary. Changes are summarised in the introduction to each approved document and highlighted in coloured text throughout the documents. The timetable for revision is also longer than that of Part L 2006, with the issue of both revised approved documents and associated revised software (SAP and SBEM) promised some time ahead of the implementation date to enable industry to prepare properly.

Overview of changes

Part L regulates the carbon dioxide emissions from buildings through the control of energy use in buildings. The requirements are set out in the Regulations, with guidance given in the approved documents. There are separate approved documents for new and existing buildings and for dwellings and all other buildings. In total there are four separate approved documents.

Now, for the first time the guidance emphasises the strategic hierarchical approach unpinning the structure of the approved documents. This can be summarised as follows:

• Reduce energy demand due to heat flow through building fabric, pipes, ducts and vessels
• Improve the energy efficiency of the building systems and ensure that they are well controlled and are properly commissioned
• Use a mix of energy supplies and renewable energy systems
• Enable users to operate buildings efficiently through the provision of monitoring and information

The approved documents reiterate their status in that they provide guidance which, if followed, is presumed to lead to compliance. However, it is highlighted that specific project circumstances could lead this to this not being the case. Designers are free to propose alternative solutions providing the requirements of the Regulation are met.

The consultation highlights some important strategic issues that the 2010 revisions will begin to address notably in the area of compliance and the correlation between design and regulatory intent and actual building performance. The proposals therefore include the following:

• A design stage carbon dioxide emission rate calculation and supporting information to enable building control to understand the key features of the Part L compliance strategy. This is in addition to the post construction calculation. This is covered in more detail later in this article.
• Encouraging the use of accredited construction details by allowing higher performance characteristics to be credited in the carbon calculation
• The wider use of competent person schemes
• Better definitions and guidance regarding renovation work
• Changes in performance characteristics to reflect “as installed” performance
• Improved compliance guides
• Clarification of the interpretation of the energy efficiency requirements to make clear that the requirements apply to all buildings where energy is used to condition the environment and does not refer to the need or otherwise for human comfort.
• Removal of statutory exemptions from the energy efficiency requirements, in particular for historic buildings, although the guidance that historic buildings require special consideration if compliance would affect their character or appearance is being strengthened.

New build Part L compliance steps and tools

Much of Part L remains unchanged from the 2006 revision albeit more refined. The five-stage compliance procedure for new build remains.

A key feature of the compliance procedure is the use of the carbon calculators (as stand alone or incorporated into Dynamic Simulation Modelling tools (DSM). The Standard Assessment Procedure (SAP) is used for dwellings and the Simplified Building Energy Model (SBEM) is used for all other buildings. These allow the designer to demonstrate compliance with the requirement (regulation 17C) that carbon dioxide emissions do not exceed a target emission rate. The setting of this Target Emission Rate (TER) is central to achieving reductions in carbon emissions.

New buildings have seen their carbon emissions target decrease in steps of 25% in 2002 and 2006. The 2010 consultation recognises that this is easier for some types of buildings than others. An exercise reported in the impact assessment, has been undertaken to determine the cost effective limits of improvement of different building components for these different building types, for which target levels ranging from 20%-30% have been allocated.

Two options for domestic and non domestic buildings were analysed, a “flat” approach and an “aggregate approach”. In the flat approach, specifications were set for each building type in order to achieve an across the board 25% reduction. It was recognised that this might not produce the most cost effective reduction in carbon emissions across the range on building types. This is because the relative significance of different energy flows (heating, hot water, cooling, etc.) varies according to building type. An alternative ’aggregate’ approach addresses this by evaluating the cost effective limits at a building component level e.g. lighting walls, floors, windows, hot water system. The specifications for each building type were developed to produce an aggregate reduction of 25% across all buildings but not necessarily on individual building types. The percentage reduction required for each building type is adjusted to equalise the cost if meeting the proposed new standards. The percentages calculated for the different non domestic types are shown below.

Table 1: percentage carbon dioxide reductions by non-domestic building type (based on 25% aggregate)

A cost benefit analysis compared the two approaches for domestic and non domestic sectors. The analysis showed that there was little difference in the net benefit of each approach although the flat approach resulted in higher energy savings.

A similar exercise was undertaken in the non domestic sector where it was shown that there was a clear net benefit of using the aggregate approach with significant cost and energy benefits relative to the flat approach.

The preferred options put forward in the consultation reflect the finding of the RIA and the approach differs for the domestic and non-domestic sectors. Hence the preferred option is a flat 25% increase in the Target Emissions across the domestic sector and a 25% aggregate decrease across the non domestic sector.

The changes will be made by adjusting the “notional” building specification which is set as a default within the software, and as such the designer will be unaware of the relative required improvement.

The calculations to demonstrate compliance will be required at the design stage submission This will be in addition to the current post construction requirement. The calculations will need to be accompanied by design specifications. It is expected that the revised compliance software will provide an extended features list with associated construction data. It is hoped that this will enable building control to identify the key strategies adopted in the design and to adopt a risk based approach to audit and improve overall compliance.

A related change which is intended to close the performance gap between design and reality is the introduction of ’credit’ within the carbon calculation to reward the enhanced performance characteristics of quality assured procedures during design and construction.

It is proposed in the consultation to extend and develop the Accredited Construction Details (ACD) scheme. ACDs were first introduced in the 2006 edition and are considered to be generic and conservative. They have not therefore allowed the full benefit of better detailing to be implemented on site or used in the calculations.

The proposal set out in the consultation envisages an industry funded scheme that maintains a database of quality assured details. Funding would be drawn from the users of the details, the quid pro quo being:

• Reduced specification required in the compliance specification
• A reduction in the extent of the air pressure testing regime
• A possible future reduction in the building control fee

It is recognised that the scheme may take time to become established. Interim provisions are therefore proposed for the use of non-accredited detailing but with the carbon dioxide benefits being somewhat lessened by additional margins.

Commissioning receives additional attention with new guidance on the provision of a commissioning plans to Building Control to enable ongoing checks to be undertaken if required.. Subsequent to commissioning, the notice required by Regulation 20C would confirm that the commissioning plan has been followed and that the systems have been properly commissioned.

Although subject to a separate consultation linked to SAP it is important to touch upon the changes proposed for the carbon dioxide emissions associated with different energy sources used in buildings. The emission factors for all fuels have been recalculated based on a consistent methodology. The most significant change is to the electricity emission factors which have been increased by 40% from 0.422 to 0.591kgCO²/kWhr (for more information, click on this link).

Approved documents

The format presented in the consultation is different from the current editions. Each approved document is divided into seven separate sections:

• Section 1: Introduction
• Section 2: The requirements
• Section 3: General guidance
• Section 4: Design standards
• Section 5: Quality of construction and commissioning
• Section 6: Providing information
• Section 7: Model designs

ADL1A - new dwellings

The definitions used in the approved document are extended and modified to reflect the changing nature of building design solutions and in some cases to provide clarification.

The government preferred method for dwellings is to continue to use the 2006 method for setting the target but reduced by a further 25%.

The comparison between the notional and actual buildings will produce a schedule which will assist building control when checking compliance. This is an important addition that should improve compliance levels.

The “backstop U-values” for all building elements required under criterion two, have been left unchanged mainly because of the law of diminishing returns. Heat loss that was hitherto considered minor has become more significant - thermal bridging is an example of this and there is greater emphasis and guidance on this subject. There is a significant benefit to using “accredited construction details” in terms of the calculation of carbon emissions when compared to unaccredited details.

There are changes to the requirements for party walls. This follows research that showed a significant heat loss through this building element. There are now minimum standards and additional guidance relating to party walls.

Lighting is also a major component in the energy use of buildings. The notional building will assume 100% use of low energy lighting with a requirement for atc least 75% of fixed lights to be low energy. This reflects the UK’s voluntary phasing out of tungsten lamps.

The third criterion, that relating to overheating has been modified to capture all dwellings and close the anomaly whereby the simple expedient of installing mechanical cooling precluded the need to meet the guidance with respect to overheating. All dwellings will therefore have to incorporate appropriate passive control measures to limit the impact of solar heat gain on indoor temperatures in summer.

In line with the greater emphasis on thermal bridging and party wall heat losses the guidance associated with criterion four has been extended and the consultation raises a number of questions relating to the use of accredited construction details.

There are minor changes to the pressure testing requirements, in particular a doubling in the frequency of air permeability testing although the minimum standard of 10m³/hr/m² remains unchanged. There are enhanced provisions in the case of a building failing its pressure test.

The guidance with respect to commissioning remains largely unaltered although there are additional procedures set out in the domestic compliance guide.

Criterion five sets out what information should be provided to the occupier - these changes are relatively minor. Guidance includes a suggestion that the data used in the calculation of the TER and DER is included in the log book along with the Energy Performance Certificate (EPC) and associated recommendations report. It goes on to suggest that the electronic input file would be useful for future use by the owner when altering or improving the building.

For those who have spare cash and anticipate long hot summers over the coming decades Part L will now require that all indoor swimming pool basins will have to be insulated.

ADL2A - new buildings other than domestic

The changes for new non-domestic buildings are modest and the major changes have been described in earlier paragraphs. The calculation methodology incorporates some minor changes, for example the calculation of the Target Emissions Rate (TER) now makes no distinction between Building Improvements and Low and zero carbon technology and allows any combination.

There is additional guidance on multi-fuelled building and for buildings connected to community heating systems. There is also encouragement to consider the use of low temperature heating systems, to design systems with future low and zero technologies in mind and to consider the impact of climate change

The general ambition is to achieve an improvement in compliance through more effective building control inspection and provision of certified information. In addition there is further guidance on the use of multiple energy supply alternatives such as biomass or community heating.

There is extensive additional guidance with respect to modular building and construction to compensate for the changes in provisions.

In addition there is guidance on shell and core and first fit-out. Where a building is offered to market without final systems installed criterion one can be satisfied by making assumptions about the final installation in terms of efficiency. Subsequently the fit out team would have to resubmit the TER/DER calculation if the assumptions were not appropriate. This would also lead to a requirement for a new Energy Performance Certificate.

The “backstop values” for most building elements have been left unchanged for reasons outlined earlier in the paragraphs on ADL1A. Designers are referred to the compliance guide for minimum standard efficiencies for fixed building systems and guidance is given with respect to systems not covered by the guide. This gives designers some freedom to select innovative approaches.

The guidance also encourages designers to allow for centralised switching to enable mangers to switch appliances off during out of hours periods. However it is acknowledged that no benefit can be accrued in the BER calculation as the loads are outside the ’regulated’ energy envelope. Opinions are sought in particular on this guidance.

The guidance on criterion three (overheating) has been extensively re-written and requires a comparison against a reference glazing case based on 40% glazed facade with glazing with a G-value of 0.46. It is emphasized that the procedure is merely a test and cannot be considered to eliminate the risk of overheating but should reduce the need and use of mechanical cooling.

As with ADL1A there are detailed amendments relating to the use and application of accredited construction details and opinions are sought.

Pressure testing remains mandatory for all new buildings except for buildings less than 500m² or where the buildings are modular. However if no testing is undertaken then the carbon calculation must assume a higher leakage rate of 15m³/hr/m².

Changes to criterion five see the introduction of guidance relating to the provision of a commissioning plan. This would need to be submitted with the design stage TER/BER calculation. This would help building control to check progress on commissioning and ensure standards are achieved.

As with ADL1A it is proposed that the TER/BER information and the EPC together with the associated recommendations report are included in the logbook

Existing buildings

It is broadly accepted that one of the greatest barriers to improving the UK’s energy efficiency and carbon performance is existing building stock. It is also recognised that Building Regulations are only part of the solution - an important part, but a part nonetheless.

There are a number of strategic changes to the Approved Documents ADL21B and 2B.

• Refinement to the definition of and guidance on renovation to clarify its meaning. The definition is extensive and only applies if the work that meets the definition being carried out equates to 50% of the surface area of the individual element or 25% of the total building envelope.
• Removal of exemptions for conservatories (under 30m2) under Part L as detailed later and the removal of exemptions for historic buildings and buildings with low energy demand. Additional guidance is provided.
• Requirement for the use of Whole Window Energy Ratings for domestic windows and whole element U values for certain glazed doors and windows in non-dwellings and to restrict the use of mid-pane U values.
• Improve testing and commissioning in line with changes for new build
• Improve guidance and the requirements for the provision of information to building Control under Shell land Core developments to enable Building control to make robust assessments of both the shell and core and the Fit out.

The consultations also seeks views on the removal of exemptions for conservatories (under 30m²) under Part L as detailed later.

The replacement of controlled services, which has been extended to include renewable energy technology, now makes reference to the standards set out in the relevant compliance guide. In the event of renewable energy technology being replaced, the new unit must match the performance of the existing unit.

The need to improve the commissioning of systems is emphasised by additional guidance for commissioning plans that identify both the extent and type of testing required. This execution of this plan should be confirmed in the Regulation 20C notice required by Building Control.

ADL1B - existing dwellings

The guidance provided allows for a both prescriptive approach or a more detailed calculation based procedure.

The consultation highlights the growing significance of conservatories upon domestic energy use and associated carbon dioxide emissions and views are sought on whether to make the compliance with Part L a requirement and whether the works would be notifiable. The guidance suggests that reasonable provision would be to ensure that the conservatory was thermally separate, have independent on/off heating controls, be constructed to minimum thermal standards and have a fixed ventilated opening provision of not less than 5% of the conservatory and the room to which it is attached.

ADL2B - existing buildings other than dwellings

The 2010 revisions have least impact upon ADL2B. In common with the other documents there is clarification of some procedures and guidance on assumptions.

Consequential improvements for buildings in excess of 1,000m² remain but with a single additional trigger, that of the addition of “an increase in the conditioned or habitable area.” There are minor clarifications particularly with respect to what can be included in contributing to the “consequential improvements”.

Not forgetting Part F

The maintenance of indoor air quality is a fundamental requirement of a building’s design strategy, whether through passive or active systems. As such, Part F is being revised at the same time as Part L. There are additional ventilation provisions for more airtight homes and the introduction of requirements for installation and commissioning. The growth of mechanical ventilation systems in dwellings has also prompted the introduction of type-testing of noise levels from mechanical ventilation systems to avoid nuisance to occupants.

Wrapping up

The 2010 revision sees another major step to zero carbon buildings. Change always brings about unforeseen complications, the greater the change the greater the complication. A 25% reduction in allowable carbon dioxide emissions is a significant reduction, bringing the accumulated reduction in emissions to 58% compared with levels in eight years ago. The 2010 revisions are unlikely to be as painful as those in 2006. Those responsible for the revisions have listened to the industry and, whilst sticking to the target reductions in allowable carbon dioxide emissions, have made an effort to ensure that the costs of compliance are optimised and that there is time for industry to prepare for the changes.