Part L1A 2013 - 10 Key Points

21/Nov/2013
Blog Author: 
Dyfrig Hughes


The Part L 2013 documents were published on Friday 15th November 2013. The updated Regulations come into force on 6th April 2014 for dwellings that have not previously been subject to a building notice, full plans application or initial notice.

Dyfrig Hughes, Product Development Director at NES, lists here what he sees as the key points in the 2013 edition of the Approved Document L1A covering new homes.


1. The 2013 document is simpler to read and much easier to understand.

2. There are now two targets to meet. As well as the Target Emission Rate (TER) the dwelling needs to meet a Target Fabric Energy Efficiency (TFEE) measured in kWh/m2/year. The Regulations have been amended to include the TFEE within the mandatory element of L1A (Criterion 1).

3. The TER and TFEE are both based upon the performance of a newly defined Notional Dwelling. This dwelling has a fixed specification for U values, heating etc that provides a 'prescription' for one way of meeting the target. However, the builder has total flexibility in the specification they choose as long as these two targets are met. The specification for the notional dwelling can be found in Section 5 page 25 of the ADL1A document and in more detail within the finalised SAP 2012 document issued on 31st October 2013 (see references at the end).

4. The TER equation is now much simpler. It no longer includes an improvement factor over the previous Building Regulations. The new target of a 6% reduction as compared to Part L 2010 is still achieved through the specification of the notional dwelling. The TER equation still contains a Fuel Factor for heating; the factors are similar to 2010 but adjusted slightly to compensate for higher carbon factors in SAP for electricity, solid fuel and LPG. The TER calculation also requires the lengths and psi values of each thermal bridge; as a consequence the only y value that can be specified when calculating a DER is 0.15 W/m2K. The aim is to encourage builders to consider thermal bridging earlier on in the process.

5. The TFEE is quite simply the FEE for the notional dwelling. This differs to the approach outlined in the consultation process held in early 2012 where separate targets were proposed for various built forms (e.g mid terraced vs end terraces).

6. Both the TER and TFEE values can be achieved using average values, as long as all of the dwellings are within a single block of flats or terrace.

7. The limiting fabric values are unchanged from Part L 2010 e.g. Wall U value 0.3 W/m2K, Air Permeability 10 m3/hr/m2. The limiting system efficiencies are as per an updated Building Services Compliance Guide and do not appear to have changed significantly.

8. There is a new section in the document called 'Demonstrating Compliance' and an associated Appendix. The document makes it much clearer that an EPC does not demonstrate compliance but is an associated output from the process. What demonstrates compliance is documentation provided by the Builder to Building Control showing that the dwelling meets the required targets along with details of how specifically this was achieved. These are needed before work starts (at least 1 day) and after work ends (within 5 days).

9. There is a new Regulation (25a) requiring builders to have documentation demonstrating that they have considered the technical, environmental and economic viability of high efficiency alternative systems i.e. renewables, cogeneration, district heating and cooling, heat pumps etc. The trigger for when features of the dwelling appear on the Key Features List (in outputs from SAP software) have been adjusted to reflect the higher fabric standards that will be promoted by the TFEE.

10. Part L 2013 covers England only. Wales will from later in 2014 have its own building Regulations based upon the same methodology but with different targets. Scottish Building Regulations will follow in 2015.

The Approved Documents for Part L 2013 and the updated Design Compliance Guide can be found here.

The finalised SAP 2012 document can be found here.

NES will, in the New Year, be providing further CPD opportunities for OCDEAs and others covering both SAP 2012 and Part L1A 2013.

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