Building Regulations Part L1a 2014


The changes to Part L came into force in April 2014 and set a requirement for new homes to achieve a 6% carbon improvement across the build mix. House builders will continue to have flexibility in how they approach carbon targets but as well as, keeping a focus on the building fabric, a fabric energy efficiency will also be introduced.

These two Notional Building targets are critical for the building to meet Building Regulations and therefore the DER (Dwelling Emission Rate) and DFEE (Design Fabric Energy Efficiency) must be no greater than these.
There are 2 ways of complying with Criterion 1 of the regulations; either by using the “elemental recipe” or by producing calculations using the Government’s Standard Assessment Procedure (SAP). The simplest form is the “elemental recipe” which is defined within the “notional dwelling specification“

If the “notional dwelling specification“ is adopted in its entirety then this will be sufficient for the dwelling to comply with the fabric energy efficiency and carbon emission requirements of Part L1A.

However, although simple in principle this will be costly to achieve due to the high levels of insulation required throughout the dwelling. This method may prove satisfactory for smaller projects but it is likely that larger developers will opt for using the Government’s Standard Assessment Procedure (SAP) for Energy Rating of Dwellings using the flexible nature of the system to achieve the most cost efficient building models.

Whether using the elemental or calculated method the CUBE6 system ticks all the boxes and we will continue to work alongside the developer to offer the most cost effective package for their particular project.

Notional Dwelling Specification

The elemental method defines the minimum requirement for each of the major parts within a development i.e. Floors, walls, windows and roof.

The values are as follows:

0.13 for floors 0.18 for walls
0.13 for roofs 1.40 for windows

SAP 2005 is adopted by government as part of the UK national methodology for the calculation of the energy performance of buildings. Its purpose is to provide accurate and reliable assessments of dwelling energy performances that are needed to underpin energy and environmental policy initiatives.

SAP works by assessing how much energy a dwelling will consume, when delivering a defined level of comfort and service provision. The assessment is based on standardised assumptions for occupancy and behaviour.

SAP quantifies a dwelling’s performance in terms of; energy use per unit floor area (TFEE), a fuel-cost-based energy efficiency rating (the SAP Rating) and emissions of CO2 (TER) (the Environmental Impact Rating). These indicators of performance are based on estimates of annual energy consumption for the provision of space heating, domestic hot water, lighting and ventilation. This enables a like-for-like comparison of dwelling performance. Related factors, such as fuel costs and emissions of carbon dioxide (CO2), can be determined from the assessment.

Target Emission Rate (TER) is the minimum energy performance requirement for new dwellings and is expressed as mass of carbon dioxide (CO2) in kg per m² of floor area that should be emitted per year.

Target Fabric Energy Efficiency (TFEE) rate is expressed as the amount of energy demand in units of kilowatt-hours per square metre of floor area per year.

Thermal Bridging is created when materials that are poor thermal insulators come into contact, allowing heat to flow through the path of least thermal resistance.

Psi Values values are a measure of the linear thermal transmittance of a thermal bridge and have units of W/mK where m is the linear metres of the thermal bridge and are used to calculate the Y value.

Y Values is a proxy for the heat loss through the non-repeating thermal bridging areas of a building. In order to calculate the Y-Value of a building, the length of each thermal bridge is measured and multiplied by the respective Psi value.

Future Developments

The Government also announced that it would shortly be consulting on the next steps to Zero Carbon Homes and also on delivering Allowable Solutions.

The Government’s commitment that ‘new homes should be net zero carbon from 2016’ represents a challenge.

In terms of accurately and robustly assessing the performance of potentially lower-energy dwellings, given that some aspects of the performance may be delivered through off-site allowable solutions.

A key aspect of SAP’s future development will be to accurately reflect carbon emissions reduction from both on-site and off-site performance measures.