Part L compliance: the practical approach to fabric first

Stephen Smith, market development manager at Knauf Insulation, discusses the recent Part L changes in England and Wales and how developers can easily comply with a flexible recipe approach

The amended Part L of the Building Regulations has finally come into force, applying to all developments registered with Building Control earlier this year. Approved Document L1A (ADL1A) now contains the revisions relevant to new build housing, which the government hopes will prove an important step on the way to its 2016 zero carbon homes target. What’s more, as of July this year, the Welsh Approved Document L1A (Conservation of fuel and power in new dwellings) came into effect – the first version of its kind for use solely in Wales.

The headline change to Approved Document L1A (ADLA1) England is a 6 per cent reduction in the CO2 emissions from the mix of new dwellings relative to Approved Document L1A 2010. The measurement of both the thermal performance and CO2 emissions associated with the dwelling under consideration will be calculated using the 2012 version of the Standard Assessment Procedure (SAP 2012). A slightly higher improvement of 9 per cent is included across non-residential buildings. Whereas, Wales targets an approximate 8 per cent reduction in the CO2 emissions from the mix of new dwellings relative to Approved Document L1A 2010. As a result, the comparison table (Fig. 1) sets out the minimum acceptable fabric performances.

The other important additions within both the England and Welsh revisions are the requirement for compliance with the new Target Fabric Energy Efficiency (TFEE), which will place increased focus on the fabric of the building and the inclusion of a notional dwelling specification that provides an example of how one may comply with the new regulation.

One of the simplest changes to the Documents is the introduction of an “elemental recipe” which is detailed 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 target fabric energy efficiency and target carbon emission rate requirements of ADL1A.

What’s important though, is the degree of design flexibility afforded by the L1A version. Developers are free to vary the specification across certain building elements, provided the same overall level of carbon dioxide emissions and fabric energy efficiency performance is achieved or exceeded.

As with any recipe the blend of ingredients can be amended to suit the needs of the individual or developer, which in this instance means that there is great deal of scope when it comes to the specification of elemental fabric U-values. Some of the U-values in the elemental recipe in Approved Document L1A may not be beneficial to all housebuilders and developers, in terms of a practical and commercial approach.

As an example, consider a cavity wall U-value within the notional dwelling at 0.18W/m²K. This requires a wall thickness between 365mm and 380mm. To achieve compliance with 2010 Regulations, the majority of volume housebuilders are constructing cavity walls to a U-value of 0.25W/m²K. Improving on other elements such as pitched roofs insulated at ceiling level (Knauf Insulation would recommend a U-value of 0.11W/m²K rather than 0.13W/m2K), it is possible to maintain the cavity wall U-value of 0.25W/m²K with an overall wall thickness of just 300mm. It is, therefore, possible to exercise the design flexibility, which has been included within ADL1A 2013 and adopt a more practical and commercially aware approach.