Part L1A & L1B Guidance
Part L of Schedule 1 to the Building Regulations provides that reasonable provision shall be made for the conservation of fuel and power in buildings by limiting heat gains and losses (SI 2010/2214 as amended). Statutory guidance is set out within Approved Documents L1A & L1B on compliance with the provisions for new and existing dwellings respectively.
The revised 2013 edition to these Approved Documents contain statutory guidance (effective as of April 2014), most notably the introduction of a fabric efficiency target for new builds, in addition to the CO2 target in advance of the 2016 requirement for all new homes to be built to zero carbon standards. The new measures afford developers the opportunity to build better, more sustainable buildings to ensure that newly-built homes deliver energy-saving benefits over decades to come. The guidance focuses on the overall build-design meeting five criteria:
CRITERION 1 ACHIEVING THE TER & TFEE RATE
This refers to the Target Emission Rate (TER) and the Target for Fabric Energy Efficiency Rate (TFEE). In accordance with Regulation 26 of the Building Regulations, the CO2 emissions from the dwelling emission rate (DER) must not be greater than the TER. Additionally, and in accordance with Regulation 26A, the calculated Dwelling Fabric Energy Efficiency (DFEE) rate must not be greater than the TFEE rate. Whilst the L1A guidance provides specifications for the fabric and fixed services of a notional new dwelling, it allows developers to opt for alternative designs, provided the same overall level of FEE performance and CO2 emissions is achieved or bettered.
CRITERION 2 LIMITS ON DESIGN FLEXIBILITY
Whilst the approach to complying with Criterion 1 allows design flexibility, paragraph L1(a)(i) of Schedule 1 to the Building Regulations 2010 provides for reasonable provision to limit heat gains and losses through the fabric of the building, and paragraphs L1(b)(i) & (ii ) require the provision of energy-efficient fixed building services with effective controls. Achieving the TFEE rate could be dependent on very good performance of one specific feature of the fabric design with poorer fabric performance elsewhere - if this key element of fabric design were to fail or perform less well than expected, this would have a significant impact on performance. Continuing to have limiting fabric standards in Criterion 2 reduces such an impact by discouraging inappropriate trade-offs.
CRITERION 3 LIMITING THE EFFECTS OF HEAT GAINS IN SUMMER
This sets out the approach to limiting heat gains as required by paragraph L1(a)(i) & L1(a)(ii) of Schedule 1 to the Building Regulations. Solar gains are beneficial in winter to offset demand for heating but can contribute to overheating in the summer. The effects of solar gain in summer can be limited by an appropriate combination of window size and orientation, solar protection through shading and other solar control measures, ventilation (day & night) and high thermal capacity. For heat gains and losses from circulation pipes, reasonable provision should be made to limit heat losses from pipes as set out in the Domestic Building Services Compliance Guide, including insulating primary circulation pipes for domestic hot water services.
CRITERION 4 BUILDING PERFORMANCE CONSISTENT WITH DER & DFEE RATES
Dwellings should be constructed and equipped so that performance is consistent with the calculated DER and DFEE rate. A final calculation is required to take account of any changes in performance between design and construction, and to demonstrate that the building, as constructed, meets the rates as required by Regulations 26 & 26A of the Building Regulations. In order to satisfy these performance provisions, and in accordance with Part L of Schedule 1 and Regulation 7, the building fabric should be constructed to a reasonable standard so that the insulation is reasonably continuous over the whole building envelope and the air permeability is within reasonable limits. The L1A statutory guidance gives detailed consideration here to party walls and other thermal bypasses, thermal bridges in insulation, edges and joints, air permeability and pressure testing under Regulation 43, as well as the commissioning of heating and hot water systems.
CRITERION 5 PROVISIONS FOR ENERGY-EFFICIENT OPERATION OF THE DWELLING
In accordance with Regulation 40 of the Building Regulations, the owner of the dwelling should be provided with sufficient information about the building, the fixed building services and maintenance requirements so that the building can be operated in such a manner as to use no more fuel and power than is reasonable in the circumstances. This can be achieved by providing a suitable set of operating and maintenance instructions aimed at assisting the occupiers of the dwelling achieve the expected level of energy efficiency. This information should explain how to control, operate and maintain the space heating, hot water and ventilation systems, together with any renewable or other technologies that have been used in the dwelling.