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Legislation

Thermal

Building Regulations Approved Document Part L - England and Wales

The 2010 revised version of ‘Approved Document L: Conservation of fuel and power’ has again been split into four parts (L1A, L1B, L2A, L2B), for different building classifications. And in essence the changes comprise higher standards for windows, and the efficiency of heating, domestic hot water systems, mechanical ventilation, air conditioning and lighting as well as the building fabric.

In addition to this, there are new requirements aiming to improve the performance of new buildings in summer so that they will remain comfortable, without excessive reliance on air conditioning as the climate changes. This essentially steers specifiers towards incorporating thermal mass, and may see more use of insulation in the cavity, rather than thermal dry-lining, which isolates the habitable space from blockwork or other high density materials. It is also possible to employ so called ‘change of state’ materials, though they remain prohibitively expensive. 

Target Emission Rate (TER) will be calculated in the same way, but with a stipulation to reduce emissions by a further 25 per cent compared with current standards for all new developments.

In England and Wales this is a 40 percent improvement over a dwelling built to the 2002 regulations and corresponds roughly with the trigger point for Code for Sustainable Homes Level 3, in line with the Government’s strategy for new build dwellings to achieve zero carbon by 2016.

Elemental U-values have been tightened so that their area weighted average is no more than 0.30 W/m2K for external walls, 0.20 W/m2K for roofs and 0.25 W/m2K for floors. Bearing in mind the lower CO2 emissions target, it is expected that housebuilders and developers will need to specify (and build) fabric elements lower than these limiting values in order to show compliance.

A design stage carbon dioxide emission rate calculation and supporting information to enable building control to understand the key features of the Part L compliance strategy, including a list of specifications and key features is required. A commissioning plan is also compulsory, setting out what systems are to be commissioned and what tests are required. SAP software will provide a list of design features that are critical to achieving compliance, which along with the specification, will aid Building Control with compliance checking.

For refurbishment projects, the latest version of Part L1B seeks to reduce fossil fuel consumption and cut down the emissions of carbon dioxide from a building when an extension is built, a material change of use occurs, or the energy status of the building changes e.g. a loft or garage conversion.

In this instance, fabric U-values have been tightened for external walls in particular with new build values moving from 0.35 W/m2K to 0.28 W/m2K and retained or replaced values moving from 0.35 W/m2K to 0.30 W/m2K. 

Conservatories under 30 square metres in floor area are still exempt from Part L, providing any walls, doors and windows separating the conservatory from the existing building are either retained or replaced, and providing the existing building’s heating system isn’t extended into the conservatory.

For existing ‘thermal elements’, including those elements that were previously not thermal elements, there is a slight tightening of the requirements. This includes garden walls that were previously free-standing but now become part of an extension, and gable walls incorporated into a loft conversion.

Section 6 of the Building Standards (Scotland)

Target Emission Rate (TER) will be calculated in the same way, but with a stipulation to reduce emissions by a further 30 per cent compared with current standards for all new developments.  Although tougher than the standards set our under Part L there is some leniency if an energy efficient boiler is installed.

If a dwelling is fitted with a boiler running on mains gas, which achieves a minimum SEDBUK efficiency of 78%, an oil combination boiler achieving 82% or one of the other types recognised, a flat roof will only need to achieve a U-value of 0.25 rather than 0.22 W/m2K. For external walls the figure of 0.30 applies instead of 0.27 W/m2K when using a less favoured heating system. The rest of the variations are listed in the table below, while for non-domestic properties, the Building Standards (Scotland) only impose the higher figures.

Finally, Scottish extensions have their own approach to thermal insulation, depending on the construction of the original dwelling, though one could be required to create new elements with very low U-values: 0.15 for floors and roofs, 0.19 for walls and 1.4 W/m2K for windows and other openings.