Part L1A – Target Fabric Energy Efficiency

By John Hough; Glass Mineral Wool Manager – New Build (Knauf Insulation Northern Europe)

The revision of Part L1A includes a new compliance criteria that recognises the importance of a Fabric First approach to meeting the ambition for Zero Carbon Homes. The new Target Fabric Energy Efficiency is calculated using the actual dwelling dimensions and the performance values in the current notional dwelling specification. These values give a good idea of the performance levels likely to apply at the next revision of the Building Regulations, but for the 2013 edition, this value is increased by 15% which seems like a sensible idea. It will allow builders to make a smaller interim step and bring focus to bear on as built performance as they prepare for Zero Carbon Homes.

Some of the U-values in the elemental recipe in Approved Document L1A guide may not be beneficial to several developers, in terms of the practical and commercial elements. In my experience, by increasing the depths and widths of products used in the building fabric normally incurs extra costs.

SemiHouse

Part L1A House Image – Copyrighted by Knauf Insulation©

For example, the wall U-value within the notional dwelling is shown at 0.18W/m²K. To achieve compliance with 2010 regulations, the majority of volume housebuilders are building walls to a U-value of 0.25W/m²K.

To build to the example 0.18W/m²K given in 2013 regulations would represent an increase of 28% – far in excess of the overall 6% 2013 improvement over and above 2010 regulations. Furthermore, a wall U-value of 0.18W/m²K requires a wall thickness between 365mm and 380mm. The Knauf Insulation elemental recipe demonstrates a relaxed external wall approach which allows for a wall U-value of 0.25W/m²K with the overall thickness of just 330mm.

The insulation saving alone is between 34% and 50% compared to the AD L1A example mentioned above. Indeed Knauf Insulation’s Technical Support Team has demonstrated how compliance can be achieved with all house types with a relaxed, yet sensible fabric approach.

The Knauf Insulation elemental recipe U-values used to show compliance, benefits all developers regardless of whether they are classified as large, regional or small. I would encourage developers to work closely with Knauf Insulation’s Technical Support Team and their SAP Assessor, to make sure that what they are recommending is best suited to the developer’s needs and not just a compliance exercise.

So, my message to developers would be to design sensibly and benefit commercially, but never compromise on quality. Building to the designed detail is imperative towards achieving Zero Carbon Homes in the future.

Further Reading;

Knauf Insulation’s Part L1A guide

Planning Portal Part L Documents

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