Building Regulations: Part L Changes Explained

What is Part L?

The building regulations are coded by subject, and run from part A to P. Part L refers to thermal efficiency standards and affects insulation and heat loss.

What’s New?

The amended regulations on energy efficiency come into effect from October — and as Douglas Adams said, “Don’t Panic”.

As with all Government documents, the paperwork surrounding the new Building Regulations is daunting – around 600 pages of it – but actually it all boils down to two main points: the method of measurement shifts from elemental U-values to actual CO2 emissions and all domestic buildings need to show a 25% improvement on CO2 emissions over the 2006 standard.

The 25% improvement in Dwelling Emission Rate (DER) is a step on the way to 2016 and zero-carbon houses. If that target is to be hit then methods of ensuring that the property is built as specified have to be put in place. There is a shift in the regulations to requiring more information, more detail and more calculations at the design stage, and to giving Building Control Officers (BCOs) more powers to inspect and enforce. Essentially, to design the house properly and ensure it is built to the design.

How to Meet Them

The requirement is to reduce the DER by at least 25%. The table (below) shows the U-values that will be needed to achieve that DER. As an example, a typical cavity block wall with 70mm insulation batts and a 50mm cavity will now need 90mm batts. This will get the elemental U-value where we want it but on its own will not be enough. Airtightness, or permeability, is the major factor, and stepping up to 7.5m3/hr will be essential. Depending on the construction system and insulation levels, 5m3/hr might be needed. The difficulty is, especially with cavity blockwork, ensuring that the standards set in the specification and drawings are met in practice — quality control on site.

The BCO (officer) has the authority, and duty, to inspect works but poor workmanship can be hidden. The only definitive authority is the pressure test carried out at completion — which can result in expensive remedial work if the standard is not met.

Accredited Construction

As U-values fall and airtightness levels increase, heat loss through thermal bridges becomes more significant. One solution is to use Accredited Construction Details (ACDs). If they are not used then the DER is automatically increased by 8%. This alone can be enough to knock a Pass down to a Fail. ACDs cover all the main construction methods (find them at the Planning Portal website) and deal with the details of how to insulate junctions, ensure appropriate air seals and avoid thermal bridges.

Renewable Energy

Installing renewable energy will always help, but be careful about what you install. Heat pumps have fallen out of favour and the CO2 emissions for the electricity consumed by heat pumps are now calculated at 0.59kg/kWh, up 40% from the previously used figure of 0.42kg/kWh. In some cases, especially air source, heat pumps can have a negative impact on the DER.

If the design is struggling to get the 25% improvement needed, then adding a solar PV system contributing to the electricity demand goes a long way to solving the problem. Alternatively a biomass boiler will have net zero CO2 emissions.

Put simply, renewable energy can be the answer to hitting the 25% reduction target on its own — given that it is the right technology installed in the right way. It is very close to be being essential now and will certainly be so for hitting the 2016 target.

Extensions

The Part L changes will also affect extensions, remodels and renovations — where the term ‘thermal element’ has been introduced to address the types of work applicable. A ’thermal element’ is classed as a wall, floor or roof, and if a ‘layer’ is being altered or added to the element (confused yet?), then it will now have to meet the requirements set out in Part L1b. Basically that assumes most extensions and material renovations. The standards for replacement windows, rooflights and doors fall in line with new builds, while conservatories under 30m² are exempt.

Supplementary Issues

Lighting, ventilation, solar heat gain and possible overheating will all impact on the potential to hit the 25% reduction target but until now have not really troubled us. The new regulations give these issues more emphasis and their energy consumption now forms part of the SAP calculation. The need now exists to consider these issues at the design stage, deal with them properly and account for their impact.

Key Changes

1. U-value Changes

2. Reducing CO2 emissions

The focus of measuring buildings has shifted to their actual carbon emissions - or the the Dwelling Emission Rate (DER). More information, details and calculations are now required at the design stage.

3. Accredited Construction

ACDs - or Accredited Construction Details - provide details of how the standards can be met. If they aren't used, it increases the DER.

The Changes: Tim's Analysis

The 2010 revision to the regulations is the third set of changes in less than a decade, each change cutting 25% off the allowable carbon emissions, and they will take some getting used to. It has not been easy for anyone building houses but we are now designing and constructing buildings that are very much more efficient than those built prior to 2002. If they are about anything the new regulations are about closing the performance gap between what is designed and what is constructed. Building energy-efficient houses has to be a good idea and if we are to succeed in that it is important that the house is built as we think it will be. And that means not putting up with the poor design and workmanship that has dogged the housebuilding industry for decades.