New Welsh Part L 2014 – Domestic New Buildings

Welsh building regulations

The first of three blogs on the new Welsh Part L 2014 Building Regulations. This one is about the changes affecting domestic new build.

The Welsh Government announced changes to the 2014 Building Regulations in Wales at a couple of very good events in conjunction with Constructing Excellence Wales (CEW) on 11th and 13th February, with various presenters from the involved partners. A link to the presentations from those events is available on the Constructing Excellence Wales website.

The new Welsh Part L Approved Documents will be implemented from 31st July 2014, with the usual transitional arrangements.

The headlines were:

  • For housing there will be an 8% aggregate improvement on 2010.
  • For non-domestic there is will be a 20% aggregate improvement.

We now have a bit more of the detail behind these numbers.  First off, there will be an ‘elemental recipe’ for a gas heated dwelling based on a set fabric and service specification, which typically will be a compliant solution and which will provide a reasonable starting point for specification. The reference dwelling is again based on the actual dwelling, but with opening area based on 25% of the Total Floor Area (TFA).

For the fabric of the dwelling, the references are:

  • Walls 0.18 W/m²K.
  • Party walls 0.00 W/m²K.
  • Floors 0.15 W/m²K.
  • Roofs 0.11 W/m²K.
  • Opaque doors Uw = 1.00 W/m²K.
  • Half glazed doors Uw = 1.20 W/m²K.
  • Windows and glazed doors Uw = 1.40 W/m²K (g-value of 0.63)
  • Roof windows Uw = 1.40 W/m²K.

NB Uw is a performance level for the whole opening including the frame, not just centre-pane.

  • Thermal bridging – The targets set are the same as for English Part L 2013 (SAP 2012 reference values), which are more stringent than the old ACD’s.

For other elements:

  • Ventilation default is naturally ventilated.
  • Air tightness for the reference dwelling is set at 5m³/m²/hr @ 50 Pa.
  • The boiler for the reference gas dwelling is in as 89.5% efficient with radiators.
  • Heating controls – time and temperature zone control is the reference (with the exception of single storey, with larger living areas e.g. flats).
  • A weather compensator is now assumed  for the reference dwelling.
  • Where a hot water cylinder is provided, a good level of thermal performance for that cylinder will be required.
  • A lighting target of 100% of fixed outlets being low energy lighting is set.

The major difference from the English Part L 2013 is that the Welsh have chosen not to introduce a Fabric Energy Efficiency target (TFEE and DFEE) and instead have chosen to tighten the area weighted limiting backstop’s for the fabric elements.

These are:

Limiting Fabric Parameters

  • Roof 0.15 W/m²K
  • External Wall 0.21 W/m²K
  • Floor 0.18 W/m²K
  • Party Wall 0.2 W/m²K
  • Windows, doors, curtain walling 1.6 W/m²K (U-window)
  • Air permeability 10 m³/m²/hr @ 50 Pa

For those buildings with other main heating fuels, the fuel factors have been retained from previous regulations (albeit rebased slightly), so compliance will vary by fuel type, but the above gives a robust building fabric foundation to base compliance on.

The AECOM presentation (from the above link) gives some potential compliance levels for a couple of typical dwellings and once SAP software is available incorporating the new Welsh targets, I will try and look at some comparative modelling for Welsh regulations and maybe compare those with English 2013 compliance levels.

Other Blogs on this topic:

New Welsh Part L 2014 – Non-domestic buildings
New Welsh Part L 2014 – Retrofit, material changes of use and extensions

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Jon Ducker is a qualified energy assessor working for Kingspan Insulation Ltd. He has an extensive knowledge of energy efficiency, renewable energy systems and sustainability in buildings with an expert knowledge of the relevant sections of buildings regulations and standards and their interactions with SAP. He provides authoritative advice regarding energy assessments for a wide range of public and private sector clients.

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