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With the government strongly focusing on the construction industry's large responsibility for CO 2 emissions in 2006, intelligent roofing design and roof-product specification can dramatically reduce the impact a building has on the environment.

GROWING PV PANELS In December 2005, the government gave early details of its Code for Sustainable Homes, whereby each property will be given a star rating that reflects it energy efficiency.

New publicly funded homes will, in future, be expected to reach level three on the starratings system, significantly higher than current Building Regulation standards.

The government also introduced new planningpolicy guidance on renewable energy in 2004, Planning Policy Statement 22: Renewable Energy - PPS22. This allows local planning authorities to set requirements for renewable energy in new buildings, as well as encouraging small-scale renewable resources in existing developments.

This is a good start and could encourage more use of photovoltaic tiles, with the technology eventually becoming far more widespread as local authorities start to implement the requirements.

Photovoltaic modules can be placed on almost any building surface which receives daylight for most of the day.

Roofs are the most efficient location for PV systems as they are oriented towards the sun.

Facades, conservatories or atrium roofs can also provide suitable environments and the tiles' flexibility makes them an ideal way to help to achieve higher levels of environmental sustainability.

VENTILATION ISSUES Part L may seem to have been around for aeons already, but new changes this April will have huge ramifications in restricting the loss of heat through the building fabric.

One aspect of Part L in particular is causing concern.

As houses become better insulated to prevent heat and energy escape, and levels of airtightness are improved, the need for effective ventilation becomes paramount. However, the issue of whether vapourpermeable underlays (VPUs), used with tiles and slates, are suitable and effective alternatives to full roof ventilation now has taken centre stage.

Failing to ventilate a roof properly can create serious damage, including warping of roof boarding or sarking, condensation on metal fittings and fixings causing them to rust, build up of mould and spores which can cause health problems and, in cold conditions, the formation of frost and ice in the roof space.

Experience has shown that the use of a VPU as the sole means of preventing condensation relies on the long-term performance of the underlay to cope with a wide range of moisture levels generated within the building in all climatic conditions. What the industry needs is clear guidance on the full requirements that apply to the installation of VPUs.

The current building regulations refer designers to BS 5250. However, it has been decided by an independent panel of experts appointed by the British Standards Institution that the use of VPUs in unventilated pitched roofs is outside the scope of the recently amended BS 5250.

Instead, the standard now refers designers to the VPU manufacturer's conditions of use contained in the product's Technical Approval certificate, issued by a United Kingdom Accreditation Service (or European equivalent) accredited technical approval body.

Contention is rife as to whether the most effective way of preventing expensive condensation damage is to use a fully ventilated roof system. VPUs offer a range of benefits when supplemented by ventilation, although their use as a sole means of controlling condensation is dependent on other factors which are crucial to their effective performance.

AIMING HIGH - PPG3 One other area of change in the industry that will really have a bearing on specification is Planning Policy Guidance 3 (PPG3). This guidance, among other things, focuses on increased-density high-rise housing. The aim is to make more use of the space available and it places a limit on the size of footprint of each plot.

The result, in roofing terms, is that roofs will have steeper pitches and there will be a greater requirement for products that are easier to install and maintain, such as dry-fix solutions. These cut down significantly on initial labour time, something that will be welcome in a roofing industry currently suffering from a severe skills shortage.

Specifying dry-fix solutions carries long-term benefits in developments of this type - steeper and taller roofs will not only bear greater wind loads but mechanically fixed ridge, verge and hip roof components will prevent damage during high winds. BS 5534 is the definitive design guide for slating and tiling and is an essential point of reference, providing guidance on detailing and fixing.

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