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The Approved Document L1A, 2013 edition was published in November alongside the Standard Assessment Procedure 2012.  These two documents bring long-awaited clarity to the subject of energy and CO2 performance targets for new dwellings and will allow house builders to begin planning their routes to compliance.

Both the Target Emission Rate (TER) and newly introduced Target Fabric Energy Efficiency (TFEE) standards are now defined by a set of Reference Values applied to a notional building of the same size and shape as the actual dwelling.

Things that all developers should know about the new ‘Reference values’ include:

  • External wall u-values are very low (0.18W/m2K).  This will push masonry construction towards 150mm cavity construction.
  • Glazing u-values are at the lower end of what is achievable with double glazing (1.4W/m2K)
  • Air permeability targets of 5m3/m2/hr will require 100% pressure testing regimes on most sites
  • It will be very challenging to achieve compliance without full thermal bridging calculations for all dwellings.  This is a step-change from Part L1A 2010 where the ‘Default’ option was often used for flats and non-traditional construction types.  Detailed calculations will be required where approved details do not exist for the selected construction type.
  • Using an Accredited Construction Detail value for lintels will achieve a value 600% worse than the Reference Value in SAP 2012.  Bespoke details and close attention to specification will be required in order to achieve the Reference Value.
  • Using a construction with low thermal mass (such as aircrete blockwork or timber frame) will provide a key route to compliance, buying flexibility in other areas for many dwelling types.
  • The use of ‘Reference values’ to determine the TFEE instead of absolute targets means that inefficient dwelling layouts, such as FoGs, will achieve compliance more easily than under the initial consultation proposal to use absolute targets detached from the actual building.
  • The Reference Values are ‘tradable’.  For example, failure to achieve a glazing u-value could be compensated for by improving air tightness.

The following table outlines the key ‘Reference values’ from SAP 2012 alongside typical values that are currently used for compliance with Part L1A 2010.

 

Table 1: Comparison of ‘Typical’ 2010 construction, and the ‘Reference values’ of SAP 2012

Table 1 Comparison of Typical 2010 and reference values for SAP 2012

 

Posted on November 25th, 2013

Author: Matthew Bailey