The Part L 2013 Consultation proposes the use of new Fabric Energy Efficiency Standards for dwellings.
Through testing of typical house types we have concluded that a challenging specification uplift is required for compliance with these standards. We also outline a number of complicating issues which may pose a risk to achieving the required standards.
Within the Government’s preferred approach for Part L 2013 there are two options with regard to the Fabric Energy Efficiency Standard (FEES): -
- ‘Full FEES’ levels of 39 (flats & mid-terraces) / 46 (end-terraces and detached) kWh/m2/yr
- ‘Interim FEES’ levels of 43 (flats & mid-terraces) /52 (end-terraces and detached) kWh/m2/yr
Whichever FEES option is ultimately chosen, Part L 2013 will require a significant change in house building practice and specification to meet these standards. We have tested a number of typical house types (with SAP2009) to determine what is required to be done for compliance with the ‘Full FEES’.
The Full FEES requires:
- Flats / Mid-Terraces: 39kWh/m2/yr
- End-Terraces / Detached: 46kWh/m2/yr
The Part L 2013 Consultation does not directly provide specific sample house types upon which the measures required for compliance with each option are assessed. It relies on the extensive work undertaken by the Zero Carbon Hub with regard to Fabric Energy Efficiency Standards (FEES) over multiple dwellings of each type.
The Code for Sustainable Homes allows averaging of the FEE for flats, but not any form of houses. This is retained in the Zero Carbon Hub report, Defining a Fabric Energy Efficiency Standard for Zero Carbon Homes: Task Group Recommendations (Nov 2009).
Despite the specifications above being in general agreement, there are a number of risk factors that may be present on some sites that would substantially increase the specification required to meet the Full FEES. These challenges include: -
- There are a number of question-marks in the Consultation Specification. For instance, does it assume the same roof U-Value for joists and rafters. If so, is this a reasonable assumption?
- In practice, how easy is it to achieve a thermal bridging y-value of 0.04? Are the improvements necessary to meet this widely understood by industry and do they require a significant improvement in construction skills?
- Can low density blockwork always be used on houses and therefore achieve low thermal mass?
- Solar gain and summer overheating risk. The above is based on use of standard glazing. However, where there is an overheating, tinted glazing may be required which reduces the useful solar gains in the winter. What additional measures are required to meet the FEES standard whilst maintaining a comfortable internal environment?
- Meeting an air permeability of 3 requires MVHR for Part F compliance and is also likely to necessitate that all dwellings are pressure tested, due to the margin of 2 that is added to untested dwellings. Is an air permeability of 3 achievable on all dwellings?