Specialist costs: Curtain walling

Research by Gardiner & Theobald has shown a continued growth in the UK curtain walling market, which has a total estimated annual value of more than £600m. Although the effects of 9/11 in New York created an immediate slowdown in enquiries, overall levels have picked up significantly over the past two years. Year-on-year growth has been in excess of 10% a year, and controlled growth is expected over the next two years.

The regeneration of Britain’s regional cities has particularly boosted demand for curtain walling. Office developments with signature architecture are now under way in Manchester, Birmingham and Liverpool, counterbalancing the slow commercial market in London and the South-east.

In residential accommodation, curtain walling has been increasingly in demand, particularly for high-rise solutions where prefabrication and quick site erection are paramount. Retail developments have also boomed. Even so, the bulk of curtain walling in the UK is still consumed by commercial office developments, and as the demand for office space is predicted to rise in 2007 and 2008, the curtain walling market will undoubtedly get much busier.

The top end of the cladding market consists of highly complex projects with an overall package value of more than £10m. This sector provides high sales volume when the market is buoyant, but it is an area with less competition as only a few specialists are able to undertake the work. Complex high-value projects are often prestigious, with the curtain walling playing an important part in the image of the building. Such buildings often enhance the reputation of companies working on them.

The Gardiner & Theobald survey reports that the majority of firms work on projects up to £5m in value.

Credit: Dennis Gilbert / View

Tender prices

The market remains very competitive with tight margins and only small inflationary rises being passed to customers. The Gardiner & Theobald tender price indices reports very low price rises over the past three years with a forecast of 2-3% over the next two years, rising in 2007/08 with a predicted market peak at 3.5% a year.

Materials account for just 30-35% of the total costs of curtain walling, with the remaining costs taken up by design, installation, production and overheads. As a consequence, the cost of curtain walling is not as sensitive to fluctuations in raw material prices as other forms of cladding materials such as profiled metal decking and sheeting. Another consequence is that any standard system will be considerably cheaper than a bespoke solution, since expensive prototype design and testing will have already been paid for and installation becomes a repetitious but efficient operation.

Along with the global rise in steel costs, curtain walling systems with large panels of stainless steel have increased significantly in cost. However, as the majority of curtain wall framing tends to be fabricated from extruded aluminium sections, the cost of steel has not had a huge impact on curtain walling. Most contractors are reporting that supplier costs are currently under pressure to maintain overall margins and competitiveness. On the other hand, increases in energy costs for the production of glass in the order of 2% have been passed on to cladding contractors by glass manufacturers. Similar increases are anticipated for all energy-intensive production processes including both aluminium smelters and gasket producers, but these should not result in large increases to tender prices.

The tender price for glass elements has benefitted over the past two or three years from European manufacturers, principally St Gobain and Glaverbell, stepping in to compete with the UK’s prime supplier, Pilkington. Other glass manufacturers in Eastern Europe and the Far East are also endeavouring to break into the UK market. Cheaper curtain walling from China and the Far East presents a potential threat to European suppliers, but only once those products have been tried and tested and meet institutional standards. However, innovation in technical development and the finite European market supply may eventually allow other products into the UK.

Design considerations

System design

Generally, the flatter the curtain walling system the cheaper it is. Where spandrels are set back or forward additional costs will be incurred.

Certain costs such as initial system design are fixed and therefore take up a smaller proportion of overall costs in larger projects. The number of systems proposed for any particular project should be minimised as each will have its own design cost and smaller manufacturing runs will mean less room for economies of scale. This will also have a knock-on effect on the installation period as installers work out the best solutions.

The most economic solution is to vary the look of the facade within one system. A good example is Mid City Place in London (pictured opposite), where two separate wall types were used, one of which accommodated three variations.

Performance

The performance of the facade must be considered in relation to other aspects of the building, such as the performance of mechanical plant. The orientation of the building will have an effect on issues such as solar gain, which will drive the need for high performance coatings.

Repetition

Costs can be saved through repetitive components. Items such as raked cutting, corner conditions and faceting should all be considered as extra-over costs to the overall curtain walling rate.

Procurement

As the choice of products continues to increase and construction becomes more complex, specialist input at the early stages of design is now essential and existing processes will continue to come under strain, as they attempt to meet these demands. Early input from specialists should ensure that designs are not over complex and therefore costly.

As a result, curtain walling specialists prefer procurement routes that involve them early on in the process, such as construction management, management contracting and two-stage traditional tendering. As well as contributing design and engineering expertise,

the early involvement of specialists can advise on buildability and pre-book the appropriate supply capacity of the manufacturing process and installation. In combination, these early specialist contributions smooth the procurement process and keep lead times at their optimum level.

Programme

Curtain walling projects tend to entail a complex sequence of design, engineering, manufacturing, transportation and logistics and site installation, sometimes taking more than two years. It therefore pays to get the programme right at the outset. A sensible timetable is required to deliver a quality product accurately to site. More than that, since curtain walling element is often a major part of the whole project, it is invariably on the critical path and any delay will have a significant effect on overall project costs.

Issues that can have an influence on the programme durations are:

• complexity of design
• design changes
• extent of performance testing
• glass – types, including sizes, curves and treatment, and availability
• complexity of manufacture
• special components, such as stone, terracotta, extrusions
• approval process
• site logistics and craneage.

Hot topics

Environmental issues and Part L of the Building Regulations

The final version of the new Part L is due late summer or early autumn 2005. It will be necessary to establish the total energy performance of a building and in particular the contribution of the building envelope. The environmental issues of Part L and their effect on overall performance will necessarily lead to closer working relationships with services consultants and an increased use of naturally ventilated facades.

Some have predicted Part L will mean the demise of the glass-walled building. Others believe that its impact will be less dramatic, given the range of alternatives and the availability of high-performance glazing.

Although the full impact of the new regulations will only be fully apparent following formal issue, it is worth noting some of the effects the new regulations are likely to have:

• Early involvement of services engineers in cladding design;
• Increased use of high-performance glazing units incorporating gas-filled cavities;
• Additional areas of solid insulated cladding;
• Increased use of “climate walls” incorporating natural ventilation;
• Increased use of external shading.

The cost implications of applying the new Part L regulations to curtain walling have still to be determined. Some specialists believe that the additional costs of some elements will be balanced by improved glass technology and greater proportions of solid or insulated panels. Others are not as optimistic.

Automated production

The majority of curtain walling and cladding contractors offer CAD/CAM technology that effectively speeds up the production design and manufacturing process. They have applied automated materials management and inventory control systems, to speed up the process, reduce costly mistakes and waste. The major curtain wall specialists now have automated production lines running constantly. However, whereas the front end of the design process has been automated along with tooling and the production of sub assemblies, the final assembly process is still predominately carried out by manual labour. This means that the assembly carries heavy labour costs and the risk of human error in terms of quality control.

It is likely to be in this area where the leading curtain walling firms will focus their investment and efforts over the next few years to bring about a completely automated assembly process and closer integration between design and production. Leading specialist contractors will only set production in train after orders come in, so as to reduce the cost of financing work in progress.

Architectural design innovations

Recent advances in flexible cladding systems can create stunning landmark buildings, such as London’s Swiss Re and City Hall (pictured on page 65). Yet the technology and techniques behind such striking projects are not particularly innovative, as all development research has already been tried and tested. This flexibility should assist the invention of more dramatic and challenging cladding envelopes, which the industry now has the experience to deliver at reasonable costs. Cladding with curves in three dimensions and individually sized pieces, although not standard, are now achievable and could impact more on our skylines.

As the glazing is the largest visible element in any curtain wall, its choice and specification is paramount to the overall appearance. Technological developments will continue to benefit the industry, with solar responsive and thermally efficient glazing becoming standard.