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Part L consultation summaryJuly 2009

BSRIA provides a range of independent Part L compliance services throughout design, construction and operation of buildings.

Life after Part L - the sequel

BSRIA's David Bleicher summarises the key changes in the Building Regulations Part L consultation document and the impact on building services and construction.

Back in 2005, when I was brand new at BSRIA, I was asked to form BSRIA's response to the new Part L, drafts of which had at the time just been released. The changes that eventually came into force in April 2006 were quite radical, including compulsory CO2 emissions calculations and airtightness testing for new buildings. The government has now released a consultation paper on changes that will come into force in October 2010.

By the time the new Part L comes into force, it will have been only four and a half years since the previous revision, and this was on top of the revisions that were made in 1995, 2002 and a minor one in 2005. Given that most parts of the Building Regulations get updated every 8-10 years, why has the pace of changes been so fast with Part L?

Basically, each update represents a step change in energy efficiency of buildings. These step changes reflect improvements in technology, and also drive further improvements. If similar step changes are made in coming years, we will eventually get to a situation where new buildings are zero-carbon, and the government aims to achieve this by 2016 in the case of dwellings, and 2019 in the case of non-dwellings. Also, the 2002 Energy Performance of Buildings Directive which required all EU nations to adopt minimum energy performance standards, stated that these standards should be reviewed at least every 5 years.

So what changes does the government propose for the 2010 Part L Approved Documents? First of all, there are the changes that were consulted on in 2008 but as yet not incorporated into the published versions. These were changes to the format of the documents to make them easier to use, guidance on the use of multi-foil insulation, and additional rules relating to the introduction of Energy Performance Certificates.

New Buildings

For new buildings, the five criteria for compliance that were introduced in 2006 will still be in place, but some of the finer detail will change:

Criterion 1: Acceptable CO2 Emissions

The big change here is a 25% reduction in the maximum emissions from new buildings. The consultation paper asks for views on two different approaches to achieving this reduction, the flat approach and the aggregate approach. These require further explanation.

Under the flat approach, the 2010 Target Emissions Rate (TER) would be 25% below the 2006 TER, which itself is derived by applying improvement factors to a notional building that meets the 2002 Building Regulations. The 2006 TER is the emissions from the 2002 notional building improved by 20-28%, depending on building type. Therefore the 2010 TER would be 40-46% below the emissions from a 2002 notional building.

Under the aggregate approach, the 2010 TER would be the emissions from a newly-defined notional building, with no improvement factors applied. The specifications for the notional building would be set such that all new buildings on aggregate would achieve the national target of 25% lower emissions overall than under the 2006 Part L. This means that the 2010 TER for certain buildings may be more than 25% lower than the 2006 TER for similar buildings. For other buildings the 2010 TER may be less than 25% lower than the 2006 TER for similar buildings. This approach reflects the fact that it is relatively straightforward in some building types to improve the energy performance by more than 25%, whilst in other building types a 25% improvement becomes much more difficult. For example, a detached house has more external walls than a terraced house - applying the same specifications for each component would result in very different target values.

Interestingly, the government's preferred approach is the flat approach for dwellings but the aggregate approach for non-dwellings. In the case of dwellings, the emissions calculation tool will still be SAP (Standard Assessment Procedure). There are some proposed changes to SAP, which is subject to a parallel consultation run by BRE. For example, the proposed new SAP is a monthly energy analysis rather than a seasonal calculation based on degree day data. Also, calculations done using the SAP worksheet will no longer be accepted - all calculations will have to be done using approved SAP software.

Criterion 2: Limits on Design Flexibility

The principle behind this criterion is that designers have considerable flexibility in how they achieve their CO2 emission target, but this flexibility only goes so far. For example, you can't specify a boiler that is worse than a certain efficiency, and there are upper limits on U-values for walls, windows etc. Most of these worst allowable standards are unchanged, but there are new standards that apply to heat pumps, and various kinds of renewable energy systems. Most of these standards can be found in two new second-tier documents which are also part of the consultation: The Domestic Building Services Compliance Guide and the Non-Domestic Building Services Compliance Guide.

Criterion 3: Limiting the Effects of Solar Gains in Summer

This criterion was introduced in 2006 to reduce the need for air conditioning and reduce the installed capacity of any air conditioning system that is installed.

For dwellings, there is a calculation as part of SAP which assesses the risk of overheating. The proposed new Approved Document L1A clarifies that even if the dwelling has cooling installed, this calculation must still be carried out, but the cooling system is ignored.

For non-dwellings, a completely new approach is proposed: The solar gains through glazing must be less than the solar gains through glazing for a reference building. For side-lit buildings, the reference building is 40% glazed, with a 10% frame factor and windows with a solar transmittance factor of 0.46. This calculation would have to be carried out regardless of whether the building has air conditioning or not.

Criterion 4: Quality of Construction and Commissioning

Three things are encompassed here: thermal bridging, airtightness testing and commissioning.

There are some proposed changes to the rules for airtightness testing of dwellings. First of all, an approximate doubling of the number of dwellings on a development that need to be tested. Secondly, a penalty in the SAP calculation for any dwellings on a development that don't get tested. This will have the effect that many designers will simply demand that all dwellings on a development get tested.

Criterion 5: Providing Information

This criterion refers to the information provided by whoever builds the building to whoever occupies it. The information should be aimed at ensuring the building uses no more energy than the designer intended. There are no major changes proposed.

Existing Buildings

In recent years, much of the effort to improve building energy performance has focused on new buildings, but in any given year, only a small fraction of the building stock is replaced. It could be argued that relatively modest improvements to the existing building stock would have much greater impact than the move to make new buildings zero-carbon. However, Building Regulations aren't necessarily the best mechanism with which to push overall improvements to the existing building stock, as they only apply when building work is carried out.

While there are some proposed tweaks, the overall message of Approved Documents L1B and L2B remains the same: whenever you carry out building work, elements of this work should meet certain minimum standards. For example when you replace a boiler, it should meet a certain minimum efficiency, and when you put in a new window, it should meet a certain maximum U-value. You don't have to carry out CO2 emissions calculations, and you don't have to do airtightness testing, although you can choose to use such methods if you feel they will give you greater design flexibility.

What has come as a surprise to some people is that there has been very little expansion in the types of buildings that require consequential improvements. As a reminder, these are energy efficiency improvements that have to be carried out to the existing building as a result of building an extension or increasing the installed capacity of heating or cooling. They were introduced in 2006 in response to the 2002 Energy Performance of Buildings Directive, and only apply to non-dwellings over 1000m2. It is proposed that this requirement is extended to dwellings over 1000m2, which if you think about it is only a very small number of dwellings. Last year's proposals for a recast of the Energy Performance of Buildings Directive included removing this 1000m2 threshold altogether, so it's a mystery why the government still proposes retaining this threshold.

Have Your Say

Whether you agree with the government's proposals for changes to Part L, or like it the way it's been since 2006, or would like to see more ambitious changes, it's important that you have your say. The consultation closes on 17th September. You can download the consultation documents, which include proposed changes to the Part L and Part F Approved Documents, and the National Calculation Method. If you're interested, you can also respond to the parallel consultation on SAP. There is yet another website where you can download consultation versions of the new SAP and SBEM software.

An email helpdesk has also been set up, run by BSRIA on behalf of CLG (, and of course if you're a BSRIA member you can call in with any enquiries and we'll be happy to help. BSRIA is running a workshop in London on 30th July, focusing on non-dwellings. The findings of this workshop will be incorporated into a collective BSRIA response to the consultation.

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