With new regulations coming in later this year. Lewis Taylor of TRADA Technology’s Building Performance Division comments on pending changes to Approved Document L. Thermal performance of new buildings will have to increase by 25% on 2006 levels
 Back in 2002, the European Union reported that 40% of Europe’s carbon dioxide (CO2) emissions were coming from its buildings, a huge percentage and one that our governments have pledged to bring under control. Every day we are being warned about the potentially catastrophic effects of global warming, but what are we doing about it? Can we help by reducing our carbon footprint? Choosing to live in a thermally efficient house, madeof a sustainable material, is one step we could consider.
A revised version of Approved Document L of the Building Regulations England & Wales (Conservation of fuel and power) had not been released by time of writing to replace the 2006 iteration. In simple terms, the 2006 version required new build dwellings to be 20% better than if they were built under the previous (2002) version. ADL 2010 will require a further 25% improvement. This step change in requirements brings us closer to the Government’s 2016 zero carbon target and brings CO2 emissions down to the requirements of Code for Sustainable Homes Level 3. In practice, to achieve 2010 targets for CO2 emissions/energy usage will require improved thermal performance and air tightness. For the construction industry, this will mean more insulation in the structure and better detailing for air tightness of new buildings. Timber frame structures can already achieve good thermal performance with 140 mm deep timber studs filled with mineral wool. Achieving future improvements may need additional fibre insulation internally between service zone battens, or rigid fibre insulation boards externally. Timber frame structures can already achieve good levels of air tightness with relative ease. External walls typically contain a polythene vapour control layer on the inside of the insulation – which also forms a very effective air tightness membrane. Taking Canadian R2000 timber frame house system as an example, this prides itself on achieving just 1.5 air changes per hour, so we know this level of performance is possible. Another noteworthy change ADL 2010 will bring is the consideration of the thermal performance of party walls, to date considered to be ‘perfect’, ie with a U-value of 0 W/m2K. In reality, it can be far from perfect. Movement of air within the party wall cavity can transport heat away from the structure, leading to far greater energy use than predicted. The proposed inclusion of party wall thermal performance will either encourage the use of solid party walls or cavity party walls with insulation fully filling the cavity to limit the movement of air within it. If a non-insulated cavity party wall is used (timber, masonry or steel) with no perimeter sealing (free flow of air in and out of the cavity), an assumed U-value of 0.5 W/m2K will need to be applied. This will have a massive effect on the calculated thermal performance of, for instance, terraced houses, where more heat could be lost through the party walls than through external walls. Timber frame buildings typically use cavity party walls. At present, most of these walls will contain some acoustic insulation between the studs. In future, we may see the inclusion of full-fill thermal insulation to party wall studvoids and cavity. Edge-sealing is achieved at present with the use of cavity barriers for fire. The use of these cavity barriers and any additional sealing measures required, as well as additional insulation, should ensure that timber frame buildings can continue to assume a party wall U-value of 0 W/m2k |
