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Technical answers: Part L compliance and system efficiency changesAugust 2014

Q1: What will complying with the new Part L guidance for housing entail?

The new Part L introduces a new criteria for compliance, which is a Target Fabric Energy Efficiency (TFEE) value. The concept of FEE has been around for a while and was calculated for the energy credits under the Code for Sustainable Homes. It is calculated through SAP 2009, but there is now a mandatory requirement to comply with a target value.

With the introduction of this fabric performance standard in addition to the TER (Target CO2 Emission Rate) values, a fabric first approach will need to be taken, but renewables or MVHR are likely to form part of most strategies for compliance.


Q2: What specific considerations will need to be made in order to meet the TFEE?

The industry has been preparing to offer solutions for improved U-values across construction types in anticipation of the Fabric Energy Efficiency Standard (FEES) standard becoming mandatory from 2016. The focus in the new Part L will however be on providing adequate information to support heat loss calculations through thermal bridging.

Some construction system manufacturers offer standard details with corresponding psi-values and software is available for designers and consultants to calculate these for bespoke details. More guidance and information on this is due from DECC.

Q3: Have there been any changes to the minimum requirement for system efficiencies?


Table 1: Recommended minimum energy efficiency standards for building services (click image to zoom)
The Domestic Building Services Compliance Guide has been updated to correspond with the current version of the Building Regulations, both for new build and existing dwellings. Table 1 lists some of the minimum efficiencies required from the heating services. However, in reality a much improved specification will be needed in order to meet the revised TER standards, (there is an approximate 6% improvement over the 2010 standards). The values quoted remain in line with the 2010 version of the guidance document.

Q4: Will there be a shift in focus for services installation and commissioning to comply with the new Part L?

Work being carried out by the Zero Carbon Hub and commissioned by CLG on understanding the gap in the
predicted energy performance of new dwellings and their as-built performance has been published in their Evidence Gathering report, which was launched at EcoBuild this year.

The report highlighted significant and consistent shortcomings in the observed procedures for the installation and commissioning of building services in new homes, with a particular emphasis on mechanical ventilation systems with heat recovery. The report also acknowledged a lack of clarity and consistency in the guidance and procedures for carrying out commissioning.

All mechanical services that operate with controls more sophisticated than simple on/off settings must be commissioned and certificates provided to the home owners. It is anticipated that developers, home owners and RSLs and Building Control officers will all be more aware of this requirement.

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