Part L

Latest - March 2011

The introduction of a revised Part L 2A of the Building Regulations for non-residential buildings is the latest move in the government's commitment to near zero carbon emissions by 2016. Average carbon savings of 25% are built into the recognised modeller schemes and this means a much more rigorous spotlight on thermal bridges, heat loss at junctions and risk of condensation. This extra heat flow is the linear thermal transmittance or Ψ value [Greek letter psi - pronounced si] with units W.m-1.K-1

For the first time the regulations extend the accredited construction details [ACDs] scheme into the non-residential sector. The aim here is to reduce heat loss by linear thermal transmission through frames and interfaces between different constructions.

Part L 2010 proposes a system of accredited details and/or approved calculation methods that demonstrate those expected targets for linear thermal transmittance will be met. Where compliance cannot be demonstrated at the design stage assessment then penalty increases in the value of Ψ up to 50% are applied, potentially making overall compliance more difficult and costly than with ACDs.

However, when the new regulations came into effect on 1st October 2010 there was no accredited construction details scheme approved by the government. In fact there is no final agreement on how such a scheme should be assessed and it is likely to be well into 2011 before ACDs are available. The prospect was that all carbon model submissions to building control bodies would then have a 25% or 50% penalty increase to Ψ values.

To prevent these unfair penalties the government was forced to issue a circular. This said that until such time that accredited construction details schemes have been approved, the calculated value of Ψ may be used in carbon models without any performance penalty being added where this has been calculated by a suitably experienced and qualified person. The builder will also have to provide information about the way the detail is to be constructed to the Building Control Body.

Euroclad has a wide of details with Ψ calculated in accordance with BRE IP1/06 Assessing the effects of thermal bridging at junctions and around openings, and BR 497, Conventions for calculating linear thermal transmittance and temperature factors, These details will be treated as accredited and the penalties in Approved Document L2A [ Section 5.7] is not applied.

Latest Technical Paper - release from Euroclad Technical

Part L - Background to approved details in PartL 2A

What is Part L and Part F?

The Government is using Part L to bring about the efficient use of energy within new and Existing buildings and is split into 4 sections L1(A/B), L2(A/B). Section L1 covers new and existing dwellings and L2 is applicable to all new and existing non-domestic buildings, such as offices, hotels and warehouses. Part L aims to limit the maximum energy usage from M & E plant and strives for better quality of construction to reduce building air leakage.

Part F is the ventilation equivalent to Part L which specifies the required energy efficiency of air handing plant, supply and extract ventilation in both local and centralised systems

The changes to Part L will require a 25 per cent improvement above current standards for every new home. An aggregate approach for improvement of new non-domestic buildings will deliver an improvement of 25 per cent overall, rather than for each individual building. This is because there is greater variety among non-domestic buildings and some will be much easier than others to make efficient. The changes to Part L will increase the minimum levels of energy efficiency for building fabric and services, so that CO2 targets cannot be achieved through renewables alone. This reflects the principle of reducing overall demand for energy. The measures will also apply to work carried out on existing buildings, including extensions and conversions, fabric renovations, replacement windows and boilers.

Part F has been revised with new requirements and guidance for installation and commissioning of ventilation systems. This will help to maintain indoor air quality and avoid adverse health effects that could otherwise have occurred due to the greater tendency to more airtight buildings arising from the Part L changes.

Part J, which covers combustion appliances and fuel storage systems, has also been revised to ensure that they continue to function safely in more airtight homes. The changes include the removal of technical disincentives to the wider use of biomass heating systems.

Why are the regulations being changed?

Energy is top of all politician's agenda - both in the UK and Europe were a key driver of the government policy is the Energy Performance of Building's Directive [EPBD]. This sets a wide range of targets that have to be met together with a testing timetable.

For background briefing on EPBD click this link

The Government set out in its 'Building a Greener Future' Policy Statement (July 2007), that new homes will be net zero carbon by 2016. To achieve this target, energy efficiency standards for new homes are to be improved by 25% in 2010 and 44% in 2013 relative to current 2006 standards. Likewise the government plan is for non-dwellings to be net zero carbon by 2019.

With the Government aiming for all new non-domestic buildings in the UK to be zero carbon by 2019, they intend to consult with industry on how this will be achieved. It is likely that following a 25% step change in 2010 similar changes will follow in 2013 and 2016, in line with the domestic scheme changes.

What are the main changes in PART L 2010?

New Buildings

Either a flat or aggregated 25% improvement is to be implemented although the details are still under discussion, it means that the Government is attempting to reduce the inequalities in the current calculation methods.

• • Compliance to Part L must be shown by an approved National Calculation Method [NCM]
  • Shell Builds will require full part L Building Emission Rate [BER] and Target Emission Rate [TER] calculations based on proposed 1st use/occupier of the building.
  • Design stage submission of Part L calculation required at planning stage.
  • Calculated U values may increase by up to 50% if a non 'approved construction' is used.
  • Commissioning plans required at planning approval stage to Building Control.
  • Energy Performance Certificate [EPC] recommendations report will have to be submitted to the building occupier.

• Existing Buildings

  • • Consequential improvements will be required if the habitable/conditioned area increases.
    • Specific fan powers are 'improved' requiring lower velocities and requiring bigger fans and ducts.

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