Ductwork priorities

A fair deal for the ductwork industry — Paul Roxburgh.
Without ductwork, air conditioning is just comfort cooling. But ductwork is not something that can be shoehorned into any space available, as Paul Roxburgh stresses.It is 10 years since ADCAS, the Association of Ductwork Contractors & Allied Services, was formed by a number of specialist ductwork contractors and suppliers to promote their own interests and — at the same time — the interests of clients of projects and M&E contractors for which ductwork contractors provide specialist contracting skills. As Paul Roxburgh, the president of ADCAS, explains, ductwork specialists in the past had traditionally been regarded as the low-tech end of the building-services industry, but that image has been steadily changing over the last 20 or so years with the growing use of computer-aided design and manufacture. Most important subcontract The traditional status of the ductwork sector belies the importance of the ductwork installation to a project, believes Paul Roxburgh. He says, ‘The ductwork contract is probably the most important subcontract placed by the M&E subcontractor. Ductwork is physically the largest service in a building. All the major pieces of ductwork are custom designed for the project and made to measure off site.’ You only have to look up into the ceiling zone of any major project to appreciate that while it can be a demanding task to route other services around the ductwork, it would be well nigh impossible to route ductwork around those other services. There, in brief, is the background to Paul Roxburgh’s belief that the ductwork specialist should be involved from the early stages of a project. ‘As soon as the M&E contractor is appointed, he should look to place the ductwork contractor.’ His own company’s experience supports this assertion. ‘We work with a number of companies who want us involved as part of the design team,’ he says. ‘For an M&E contractor working on a design-and-build contract, there are great benefits to be gained in getting the ductwork contractor involved right at the start. A key benefit is ironing out co-ordination problems between ductwork and other services at the outset — right back at the CAD station. The first step to a successful ductwork installation is co-ordination, or all the specialist sub-contractors will try to use the same space.’ Partnering The message is getting through. Paul Roxburgh tells us that well over 75% of ductwork contracts in the UK are carried out as a specialist contract for the mechanical-services contractor. ‘A major development of late is the use of partnering, with a good team on one contract tending to be kept together on the next one.’ Throughout its 10-year history, ADCAS has tackled both technical and commercial issues — and is making headway. One area of concern is the huge proliferation of component sizes that are specified for components such as grilles, diffusers and spirally wound ductwork. Whereas designers accept standard sizes for pipework and valves, they seem to want to specify ductwork components with a variation of just a few millimetres. Such precision means that, in principle, there could be as many as a million different sizes of diffusers, grilles and plenums.

The first step to a successful ductwork installation is co-ordination, or all the specialist sub-contractors will try to use the same space. Ductwork should be the first service to be installed.

Paul Roxburgh is not concerned about making rectangular metal ductwork to precise dimensions, since it is virtually all made to specification from 4 t coils of galvanised steel, rectangular ductwork accounting for some 75% of demand. Galvanised steel is the only sensible choice of material, being robust enough to withstand the rigours of a typical building site and accounts for over 95% of all ductwork manufactured in the UK. What does concern him is the plethora of sizes of other components making it virtually impossible to stock anything for immediate supply. Take, for example, small-diameter spirally wound ductwork — sections of which are held in stock. Paul Roxburgh queries whether such ductwork needs to be supplied in sizes as close as 300 and 315 mm in diameter or 150 and 160 mm in diameter. To address this issue, ADCAS members have compiled a list of rationalised sizes for circular ductwork and are now looking at terminal devices, endorsed by HVCA, BSRIA and FETA. Paul Roxburgh explains, ‘The potential benefits are enormous in terms of more efficient production and stocking policies, easier installation and cost cutting at every level — which should mean higher profits for all concerned.’ Pressure testing Another practice that Paul Roxburgh queries is the value of the requirement to pressure test a complete installation. He explains, ‘Ductwork that is properly made and installed will be pressure tight as specified in DW/144. Indeed, there is no requirement in DW/144 for testing low-pressure ductwork, which accounts for 75% of conventional ductwork systems, to be tested.’ He wonders if the requirement of Part L for buildings to be pressure tested is leading to the belief that ductwork must also be pressure tested. He does, however, suggest that random testing might be appropriate — though not more than 10% of an installation. He asserts, ‘Pressure testing an entire installation is an unnecessary technical requirement, and there is a premium to be paid for it. Such testing requires a lot of manpower to confirm that an installation is fit for purpose. But technical issues aside, what Paul Roxburgh sees as unfair commercial practices are a serious concern. He explains that that, ductwork pro-rata requires more investment than any other building-services discipline. To be a major player in the industry and deliver the products and services required demands a fully functional modern factory — which requires a large investment. ‘This commitment needs to be recognised in a fair price for a job and fair payment terms, as well as fair valuation of variations, timely payment for work done and no retentions.’
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