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Theme: cladding and curtain walling

The recent influx of acts, regulations, directives and legislation will cause a profound collective change in the facade industry, with designers, architects and engineers rethinking their approach to both design team collaboration and effective product manufacture There is a lot of bedtime reading around for the facade industry at the moment - try the gripping Sustainable and Secure Buildings Act 2004 for starters. That's the one that effectively handed the ODPM the power to amend the Building Regulations - again.

This hefty tome was a precursor to the blockbuster revision to Part L of the regulations.

Another page-turner is the EU-originated Energy Performance of Buildings Directive, flying off the shelves, ready to be enforced in January 2006. If sleep still escapes you, try the 2003 Energy White Paper. That's the whodunnit in which the government puts the UK on the path to cutting carbon dioxide emissions. Possibly not one to suggest to your book group.

Digesting this lot is causing many facade designers, architects and engineers to reach for the indigestion tablets. Yet the outcome from all this legislation will be profound: a collective change to the way facades will be designed, in turn influencing design-team collaboration and product manufacture.

Carbon emissions are the main contributor to global warming and about half the UK's CO 2 emissions come from buildings. Therefore, something has to be done.

'The aim is to develop buildings that keep energy levels down, ' explains Ant Wilson of FaberMaunsell, neatly condensing the legislative paper chain into one short sentence.

The impact on the facade industry will be immediate. The new Part L, due to come into force in 2006, requires new buildings to possess an energy rating. New and refurbished buildings will need a certificate that states the building's energy consumption.

Facades provide the opportunity to engineer down a building's heat losses and solar gains. Once the facade solution is in place, internal spaces can be dealt with, either mechanically or naturally, treating the areas that the facade cannot influence. It's a tradeoff - focus the money and effort on the facade design, or on mechanical systems. The facade, a fixed element, presents a more valuable long-term option than services plant, which needs maintenance and replacement over time. However, the more moveable elements that a facade contains, such as solar-control actuators or window-opening devices (mechanical or user-controlled), the higher the cost per square metre of the building envelope. This has to be traded off against any savings in mechanical services that can be made. A double-skinned facade, such as the one designed for 30 St Mary Axe by Foster and Partners, is the most expensive design solution but does provide opportunities for natural or mixed-mode ventilation in buildings that would otherwise be sealed.

All this means that the facade will have to do more work than ever before to keep out heat loss in winter and control solar gain in summer. Facade engineers and designers will have to put even more effort into getting the design right at the early stages of a project. A well-designed facade can reduce the amount of work required by the building services, or even obviate the need for heating, cooling and ventilation systems to run all year round.

The proposed Part L amendments do at least acknowledge the catching up the facade industry will face in order to develop systems and products that meet the new standards, as well as a yet-to-be-specified phasing-in period for airtightness provisions and in Part F for larger natural ventilators.

Not hot air 'Facades are not elements that keep out the cold, ' says Wilson. 'They have to be designed to modify the climate in both directions. This means calculating to avoid solar gain and intolerable internal climates, dealing with radiant heat in spaces where there is a lot of glass, as well as sound, heating and running costs.' He maintains, somewhat controversially, that architects, faced with the increasing complexity, are keen to devolve responsibility for the facade in terms of performance and construction logistics, while keeping control of the overall design aesthetic. 'Fully glazed, triple-glazed facades may look fabulous but they are expensive, ' he argues, suggesting that the correct balance of glass and other material infill panels might be a better performance and energy-consumption-driven solution for a new building.

The proposed amendments to Part L will look for a building's carbon dioxide footprint, checking that the building fabric is essentially no worse than current U-value requirements and seeking improvement in energy efficiency of new buildings (and a reduction in carbon emissions) of around 25 per cent. The amendments also include setting performance standards for buildings as a whole rather than for construction and services elements, and will firm up on precompletion testing of airtightness. These improvements, effected in 2005, should lead to a reduction of more than 1.1 million tonnes of carbon output per year by 2010.

The new emphasis on CO 2 emissions is a distinct move away from the previous Part L, which was energy-use focused, based on the premise that the building should 'use no more energy than is reasonable in the circumstances'. The proposed changes leave it up to the developer and design team to decide how best to achieve the improvement, through 'reasonable provision made to limit heat gains and losses through the fabric of the building'. Furthermore, they indicate that 'new buildings shall be designed and constructed to avoid excessive solar gain, and thereby minimise the need for mechanical cooling'.

According to organisations conducting the building airtightness tests, many new buildings are still failing the airtightness requirements laid down in 2002. Rod Bunn of the Building Services Research and Information Association (BSRIA) says: 'Partly this is a reluctance or an inability of the building control offices to enforce the regulations, and partly it is a lack of understanding by builders and architects of techniques needed to make buildings airtight. However, with regulations in energy consumption set to tighten even further, the pips will really begin to squeak.

'Architects will have to provide the right detailing to ensure the builder can achieve the required level of airtightness. If the architect fails to deliver, but the building services engineer has designed out perimeter heating on the basis of an airtight and well-insulated envelope, poor comfort conditions will inevitably lead to litigation. Best get it right first time, ' he adds.

The principle aims will have a direct impact on facade design, aiming 'to improve the sealing, and hence airtightness, of buildings, reducing the numbers of poorly sealed buildings'. The proposed worst acceptable pressure-test performance standard is set at 10m 3/h/m 2 at 50 pascals, compared with the current average value of 12m 3/h/m 2 at 50 pascals. The distribution of airtightness achieved in response to the 2005 amendment will not be known for several years.

However, few current buildings are more airtight than 3m 3/h/m 2 at 50 pascals, so this has been adopted as the design target for the ventilation provisions given in the proposed Approved Document F (ventilation). Better add that one to the reading list as well, then.

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