Cast Iron choice for Birmingham drainage

The multiple benefits of cast iron drainage systems are playing their part in the major regeneration of one of Birmingham city centre’s traditional shopping areas. Whilst strength and flexibility are the key factors in the specification of cast iron systems throughout Bullring, it is aesthetic qualities that have scored for the adjacent revamp of the city’s Moor Street Station.

Due to be opened in September 2003, Bullring is a £500 million scheme being undertaken by developers The Birmingham Alliance, a consortium of Hammerson Properties, Henderson Global Investors and Land Securities, to create 1.2 million sq ft of shopping.

The three-level scheme designed by architects Benoy, which occupies a 26 acre site, will see more than 140 shops, cafes and restaurants, over 3000 new car parking spaces plus open spaces, walkways and performance areas. Two major department stores – Selfridges and Debenhams – will anchor the scheme. At the nearby Moor Street, a scheme is underway by The Birmingham Alliance to transform the old station into a brand-new gateway to the city as part of the overall regeneration of the Digbeth area.

With the exception of the department stores, the Birmingham office of the WSP Group is acting as building services consultant for the entire scheme. Senior public health engineer Jeff Bethell was involved in the specification of the drainage for Bullring and explains how cast iron met stringent requirements both below and above ground: “Below ground, it is the strength of cast iron that matters most. In a major civil engineering job of this kind, you have to take into account site conditions. You know that once you have trenched out, laid the drained and then re-filled the trenches, it could be up to six months before the slabs go down. This means that there is considerable heavy site traffic running across the ground. It is a factor that is very easy to overlook, but at this stage, particularly in wet conditions when the ground can be very muddy, the drainage can be very vulnerable. Only cast iron has the strength to withstand this sort of treatment.”

Above ground, two other key factors come into play – versatility and safety. Like most large retail complexes, Bullring is a speculative development with a specified number of retail units designed in. Normally, there would be one soil stack installed per proposed unit, with perhaps two for larger stores. However, tenants may wish to divide or expand units which would call for changes in drainage pipework. Jeff Bethell: “Cast iron is our material of choice because of that element of change. At one stage, a stainless steel spigot and socket system was considered but this would have meant cutting pipe out at a later stage to make changes. Modern cast iron systems are flexible because they are de-mountable and it is an easy process to add new pipework.”

From the point of view of safety in this type of scheme, which serves a catchment area of 4.3 million people, cast iron drainage systems offer the soundest option, as Jeff Bethell points out: “With cast iron you haven’t got to worry – it’s fire rated and that’s it.”

Fire resistance is one of the significant advantages highlighted by the Cast Iron Drainage Development Authority for large public schemes. It is flame proof for 4 hours and in practice, fire cannot be propagated in cast iron networks. Nor does it emit toxic fumes. For the installer, there is the advantage that cast iron does not require additional measures such as fire sleeves or cladding, factors which are significant in some of the systems being installed in Bullring.

These views are echoed by the specifiers for the prestigious Selfridges building which is destined to become a new and very spectacular landmark for Birmingham. Designed as a state-of-the-art department store, it is the quest to create a unique focal point for Bullring that has driven architects Future Systems. The exterior of the £40 million building will be covered in 15 000 spun aluminium discs. Inside, with each themed floor designed by a different architect, an ‘organically shaped’ atrium will create shafts of natural light within the shopping space. The drainage and rainwater systems, however, rely on the more traditional values of cast iron. Consulting engineer for the Selfridges project is Arup. Terry Watson of Arup expresses the opinion that cast iron is the best system available because it gives the strength needed in a scheme of this type. With a number of other services to be taken into account, it is inevitable that the pipework will take a lot of knocks and cast iron is easily the material of choice. And again, factors such as fire resistance and flexibility figure high in the equation.

In the main Bullring development, the benefits of cast iron will be hidden from public view, whereas at nearby Moor Street station it will be looks that count. The Edwardian listed building, that has lain derelict since 1986, is to be refurbished in a 1930’s style, with brickwork, colouring, signage, fixtures and fittings chosen to reflect the era. Wherever possible, existing features are being retained and refurbished. New cast iron rainwater systems have been specified to reflect the period design.

The CIDDA hotline number is 0121 693 9909.