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Theme: roofing

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If you are designing roofs today, you need to think both about dealing with the problems of the past, such as transforming failed flat roofs to pitched, and about addressing the future and the increasingly stringent regulations with which you will have to

Modernist sensibilities and advances in roofing technology have ensured a continuing market for flat roofing. But a large proportion of flat roofs specified for public buildings in the 1960s and 1970s are being replaced with pitched, or 'otherwise-shaped', alternatives.

High-performance membranes have made considerable inroads in this area, as have metal 'over-roof' systems, such as Alumasc's flat-topitch system, which incorporates a lightweight structure with a profiled metal covering.

'Standing seam roofs are very much in vogue at the moment, thanks to their flexibility and the design opportunities that they provide to architects, ' says Alumasc's business manager for metal roofing, Tony Davis. He warns, however, that many systems can struggle to meet increasingly stringent technical requirements.

The Achilles' heels of many systems are cold bridging and air leakage. According to Davis, it is down to the detailing: 'Poor detailing will spoil an otherwise good roof system.

Clients should protect themselves and ask for a warranty.' Single-ply roofing, such as the Evalon system from Alwitra, provides architects with the opportunity to specify what looks like traditional metal roofing, complete with standing-seam detailing, but is, in fact, a cheaper alternative.

Opening up space Quick to deny any move away from flat roofing, Phil Jarratt, technical manager of National Federation of Roofing Contractors (NFRC) nevertheless acknowledges the large number of flat-to-pitch roof conversions on domestic blocks in and around London.

However, Jarratt believes that the biggest trend in roofing is the growing perception that a roof is much more than just a covering for a building. 'Roofs are becoming places on which to put things', he explains, 'be it photovoltaics, heating systems or even gardens.' Even with domestic residential applications, designers are adopting a much more European approach, he explains: 'The big space at the top of a house - for example the loft - is a very British peculiarity. Rather than leaving a cold roof, designers are now putting insulation above the rafters and capitalising on this previously wasted space.' David Rowley, a partner with Nightingale Associates, urges better use of the space created by pitched or shaped roofs.

He is particularly keen on using top floors to create open-plan areas that exploit natural daylight, but emphasises the importance of understanding ventilation issues and the installation of controllable mechanical ventilation systems, 'not just in line with Part L, ' Rowley explains, 'but also with the Sustainable and Secure Housing Act'.

Almost the real thing Prefabrication is another area of growing interest for the roofing industry, observes Phil Jarratt, with many contractors now considering assembling roofs at ground level. He acknowledges that the construction skills shortage is having 'a big impact' on roofing, and while the roofing industry might deny it, prefabricated or pre-assembled components are becoming increasingly attractive from an economic point of view, he says.

Jarratt also warns that we must not lose sight of heritage roofing requirements:

'There are a lot of old buildings in this country, and a great demand for traditional products and skills'. The NFRC is working closely with English Heritage to overcome this burgeoning problem by establishing a register of individuals with traditional roofing skills, particularly stone slaters.

While this move will no-doubt address some aspects of the construction skills shortage, a number of manufacturers are now responding to requirements for traditional products. For example, noting that 'the nation's heritage is being diminished by the lack of good quality second-hand peg tiles', Keymer Tiles has launched a range of handmade Wealden clay tiles, designed to look like the old peg variety. As well as filling a gap in the market, the company claims that 'the Restoration range will provide specifiers and building owners with peace of mind in terms of comprehensive guarantees'.

All set for change? The government's commitment to cut carbon dioxide emissions in line with the Kyoto Agreement has already introduced a number of important changes for roofing suppliers and specifiers, and forthcoming amendments to building regulations will herald even more.

The traditional method of designing and specifying a roof - perceived by many developers to be the most expensive component of a new building - looks set to change beyond recognition. Gone are the traditional requirements for designers to demonstrate U-values; the new Part L regulations, scheduled for implementation in January 2006, and designed to address conservation of fuel and power, will require the calculation of a whole building CO 2 emission rating, based upon the operational energy use of the building.

While the new Part L promises to introduce an element of design flexibility, allowing architects to trade off emissions between floors, walls and the roof, the o verall building must comply with what are generally considered to be quite onerous target values.

'It's no longer an elemental approach, ' explains Kevin Ley, technical manager at Lafarge Roofing, 'and overall, buildings will have to be 25-27 per cent more energy efficient than under 2002 requirements.' And the stipulation that a pre-completion air leakage test be conducted on all new buildings, including smaller domestic properties, promises 'more than a few problems', he adds.

?and the birth of big business As designers, developers and roofing contractors struggle to understand and accommodate forthcoming revisions to the Building Regulations, including Parts C and F (relating, respectively, to the control of moisture and contaminants, and to ventilation) as well as those proposed for Part L, there will be a number of business opportunities for specialist suppliers and contractors. The big winners are likely to be the insulation suppliers, and those companies supplying rafter-level rigid boards for rooms in roofs - increasingly popular features of new homes thanks to the density requirements of PPG3. Likewise, manufacturers of energy-efficient roof windows and products for achieving well-sealed ceilings, such as better-quality loft-hatch modules and recessed lighting, and sealants, are also set to benefit under the new Building Regulations, as are those companies supplying vapour-permeable roofing membranes.

On the roof itself there are opportunities for renewable energy systems, including PV (photovoltaic) panels, and solar waterheating systems designed to supplement the energy demands of combi-boilers. Building Integrated Photovoltaic (BIPV) technology and performance are now at levels that make PV an attractive, sustainable and highly effective renewable option. Bruce Cross, of PV Systems says: 'The advances in power outputs, applications flexibility and design means that almost nothing is impossible for PV.' But there is another, potentially worrying, side to the energy efficiency coin:

assuming the trend for hotter summers continues, how will those individuals living and working in extremely well-insulated buildings cope with the ensuing increase in solar gain? If not properly addressed, this could mean energy savings from effective insulation being lost, quite literally, through open windows. It might also herald an increase in the popularity of air conditioning units - potentially disastrous in environmental terms. Yet here too lies a possible business opportunity, this time for companies specialising in radiant barriers. These include passive design measures such as specialist foils, designed to minimise solar gain, and those supplying self-controlling, mechanical ventilation systems, particularly those incorporating heat-recovery devices.

Ley describes new Part L insulation requirements for replacing roofs as 'quite a radical, cost-adding change', and predicts that Part L amendments will have a huge impact on the renovation market and might even discourage re-roofing, 'unless it's really urgent'.

The requirement that 10 per cent of the cost of projects over £8,000 be allocated to energy-efficient improvements to existing buildings, represents a further opportunity for photovoltaic (PV) technology and its suppliers. PV Systems is currently working on a number of municipal and commercial solar roof projects across Europe where, according to Cross, 'solar PV is already firmly established as a viable and welcome refurbishment choice'.

While increasing demands from the building envelope as a whole are good news for suppliers, it is not necessarily for those companies supplying complete roofing systems. Under the new, more holistic Part L requirements, even a complete roof system is treated merely as a component of a building. Paul Hanratty of CA Building Products explains: 'Although we feel that this next development will be to the advantage of those who believe in fully-tested and certified systems such as ours, we're acutely aware of our dependence on good workmanship.

'If it isn't installed properly and the construction allows excessive air leakage, everything is wasted, ' he adds. 'The detail is so important. Putting in more insulation is not the answer, as you soon reach the point where is has a minimal effect on the building as a whole.' In a bid to prevent poor installation, CA provides contractors with full details for the junctions for its systems, all of which have been run through Trisco, the BRE-approved thermal-transmission calculation software.

Moreover, the company insists its systems are only installed by operatives who have satisfactorily completed its in-house installation course.

'The focus comes down to how tightly building control decides to police building regulations', Hanratty concludes. 'So far there's been little or no burden of proof required with regard to testing, but judging by the noises now coming from the ODPM, policing is something they're planning to tighten up considerably.'

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