Home Features TECHNICAL: Part L focus on fabric first to improve thermal efficiency

Part L has been reviewed and its requirements for thermal efficiency of buildings have been tightened yet again, and this particular Approved Document deals with issues directly related to our sector. Steve Halcrow, FPDC’s technical director considers the implications.

Over many years now we have seen Part L, the Building Regulation Approved Document concerned with thermal efficiency of buildings, changed on several occasions to continually tighten the performance requirements and ultimately reduce carbon emissions in line with government’s aspirational targets.

The aim of all the reviews and improvements to Part L remains essentially the same through each generation of the document, and that is to improve carbon efficiency and work towards the notional target of zero-carbon houses by 2016. I say “notional” because, although it is a stated government objective to achieve this target, the reality is that doing so is extremely difficult and is unlikely to happen on time. The overall aim is to reduce CO2 emissions by more than six million tonnes each year towards the 2016 deadline.

As it stands, the target reductions in question are 6% for new build homes and 9% for non-domestic buildings compared with the previous levels in the Approved Document of 2010. The government’s original intention was to achieve 8% and 20% reductions respectively, according to the original consultation. The government acknowledges that the changes are later than desired, and that it has had to compromise from the original intention, but maintains that they should still result in £16m of savings to businesses and homes.

The key focus is on a “fabric first” approach, with the introduction of the “Target Fabric Energy Efficiency” assessment in addition to carbon dioxide targets. This will put more emphasis on the type of materials used in the building fabric and the design detail of their installation, whereas previously we have been used to concentrating on Elemental U Values.

In simple terms relevant to our members, greater and greater focus is likely to fall upon the type and thickness of insulation materials used, the installation of these products and of vapour barriers and (especially) air tightness membranes, and  the correct and thorough sealing of al elements to prevent undue loss of air tightness performance. Manufacturers will no doubt be working to develop new insulation products that can meet the requirements, and even then it is likely that greater thicknesses of insulation will continue to be called for. They will no doubt also be seeking new methods for off-site fabrication and the opportunity to take more of the work away from the construction site and into the factory, where conditions are more controllable.

This means that some of the constructions most familiar to us may have to be reviewed to accommodate the additional thickness, and new measures will start to be seen. Internal party walls, for instance, have long contained insulation for acoustic purposes but now we are seeing more instances of them being fully filled with thermal insulation in order to boost the overall performance of the building. Internal linings to external walls are also likely to need to accommodate greater insulation thicknesses, and detailing of air tightness measures will be scrutinised increasingly closely.

As ever, changes to the Building Regulations bring with them a learning curve for all of us to tackle. Part of the key to this is keeping up to date with the changes for yourself as much as possible, whilst of course the FPDC will monitor the situation and bring news to members via email, website and through training events and seminars where appropriate.

Useful links

http://www.planningportal.gov.uk/buildingregulations/approveddocuments/partl/changes

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