Lead times

Spotlight on roofing
Material selection
The roof of a building must work in harmony with the insulation and ventilation to keep the building free of moisture and create a pleasant environment. The choice of materials as a covering has grown with the development of material technology, both in terms of weatherproofing and also more innovative considerations such as photovoltaic coverings to produce electricity and reflective coatings to prevent excessive heat gain.

Roof designs and the materials used differ for residential and commercial buildings, with commercial buildings typically using low-slope or flat roofs and residential roofs usually being pitched. With each roof type comes different concerns regarding moisture, standing water, durability and appearance, and this is reflected in the options available for roof coverings.

Roof design can impact on a building's thermal performance. For example, in metal-framed buildings the eaves can act as a thermal fin, moving heat out of the building and thus reducing the heat-load demands on the air-conditioning systems.

Revisions to Part L of the Building Regulations have made thermal performance paramount in the thoughts of designers and clients. Roof materials have been developed to provide thermal properties as well as weather protection. Materials with good U-values, such as prefabricated metal sandwich panels with integral insulation, are therefore gaining market advantage.

The types of roofing that achieve this can be categorised into the following three groups: Metal roofing
Most metal roofing products have historically consisted of steel or aluminium, although copper and zinc are becoming more prominent. Metal roofs are generally formed from prefabricated sheets or panels, rather than blocks or built-up members. They are mainly laid with minimal slope and provide weather protection as effectively as any other roofing material.

The lightweight nature, ease of fixing and commensurate capital cost savings of metal roofing have made the material more popular in recent years.

Flat roof coverings
Flat or low-sloped roofs on commercial, industrial and institutional buildings traditionally use built-up roofing. This consists of layers of asphalt laid on a roof deck, in conjunction with a vapour retarder, final surfacing material and insulation membrane. A bitumen-felt membrane assembly consists of alternate layers of felt and bitumen, with a reflective surface finish. Single-ply thermoplastic membranes, the most common being PVC, are based on plastic polymers, which provide strength, flexibility and durability.

The advantages of prefabricated sheets over built-up roofing are the consistency of the product quality, the versatility of their attachment methods and, therefore, their broader applications.

Pitched roof coverings
Pitched roofs are traditionally covered with small tiles of slate, clay or concrete that are durable, aesthetically pleasing, low in maintenance and have inherent fire rating due to the non-combustible nature of the material. Most roof tile makers offer warranties of up to 50 years, or for the lifetime of the structure. At the end of the roof's life, these naturally occurring materials can be easily recycled.

Due to the thermal capacity of tiles and the ventilated air space that the pitch creates, a tiled roof can reduce air-conditioning costs in hotter climates and produce more constant temperatures in colder regions.

In recent years, manufacturers have developed water-shedding techniques, as well as adhesives and mechanical fasteners for high-wind situations. Because the ultimate longevity of a tiled roof also depends on the quality of the subroof membrane and structure, roof tile makers are working to improve flashings and other aspects of the underlay system.

Tender prices
The Gardiner & Theobald LLP tender price indicator for the first quarter of 2004 is forecasting a modest increase in roofing tender prices over 2005 and 2006. The increase in raw materials prices, for steel and aluminium, has affected the metal roofing market and are being passed on in higher tender prices. However, the materials price increases of 10-15% for aluminium and 30% for steel have translated into only a 2-3% overall increase in tender prices.

Asphalt roofing, on the other hand, has declined in tender pricing during the first quarter of 2004. This is expected to continue during the year, ending 4% down on 2003 levels. Respondents to the G&T tender price survey suggest that 2005 will be flat with a modest 1% or 2% increase in 2006, but oil price inflation may yet change this outcome. These figures reflect competition and trends in the selection and use of different material types in the UK market.

Of the contractors surveyed, all were concerned by the lack of major new-build contract awards, which has meant trimming margins and reducing overheads. Contractors are seeking more PFI-procured work where the life-cycle performance and maintenance cost of the roof is a significant factor when deciding on specification and use. The cost of bidding in PFI markets is high, with a limited success rate unless the firm is named in the initial specification. The larger roofing contractors are seeking a market advantage through assisting the designers at an early stage and developing the detail of their design and specification to suit their products. This ensures they are chosen for the work, reduces the cost of installation and facilitates the provision of a performance guarantee which is still an important issue for building owners.

Market conditions
The roofing materials market has grown over the past five years with overall output in the industrial and commercial sectors increasing by more than 21%. The major share of the market is for repairs and replacement of roofs rather than new build.

According to the latest survey from Market & Business Development (MBD) the majority of roofs in the UK (in terms of area) are clad with lightweight steel, accounting for some 41% of the market coverage. This is an increase in its market share of more than 50% since 1999 and reflects the trends in architectural design for lightweight, lower cost roofing solutions.

Aluminium has seen a similar percentage growth in market share but represents only 1% of the total comparable coverage of steel. Metal roofs account for the greatest share of new build work in the UK, being used on 54% of industrial and commercial buildings.

Residential pitched roofs have maintained a consistent market share and, despite anecdotal evidence that more homes are being built every year, the roofing market figures do not reflect this.

Other materials have maintained a consistent market share with the exception of concrete tiles, which has declined, and single-ply PVC, which has increased.

The improved performance of plastic coupled with generous guarantees from manufacturers has led to the increased use of single-ply PVC. Architectural designers benefit from the manufacturers' design services and can incorporate standard detailing at inception stage. Coupled with the physical flexibility of the material, this gives the roof designer more confidence in performance.

Forecasts for the market from MBD indicate a very stable period with overall output maintained at a level marginally higher than that for 2003. Little change is anticipated in each type of roofing sector year on year, with the exception of a modest increase in total coverage output in 2006 and 2007, reflecting the predicted upturn in overall construction market output.

Future developments
The roofing industry is developing products that reuse waste from other industries. For instance, recycled car hoses, tyres and other rubber products are now being utilised in a lightweight rubber "slate" tile. This is under trial in the USA at present but could be exported to the UK shortly.

The reuse of concrete and slate tiles has been occurring for centuries during roofing repairs and maintenance, making roofers, masons and joiners, unwittingly perhaps, some of the first green contractors.

Photovoltaics are forecast to continue as a roofing material, but need to develop as an integral stand-alone weatherproofing system rather than an additional layer on top of the weatherproofing defence.

Roofing will be affected by the requirements of the forthcoming revisions to Part L which introduce more onerous conditions of thermal performance. This should lead to roofs being used even more creatively to generate value from passive solar-shading overhangs. The impact of roofs on the skyline of our cities will continue to raise the profile of this element.