United Utilities needed to find a site between west Manchester and Liverpool docks for a waste processing plant to comply with a directive ending marine disposal by 1999. Achieving planning permission was going to be difficult: hiding an incinerator in the flat Mersey Valley was impossible, and opposition would be stern. The tight timeframe added to the challenge. Could creative design open the way?

Incinerators are tall, ugly, and usually left uncovered. Not here. Working in tandem with process engineers, we were able to split the facility into its component parts, so enabling the design of a series of buildings with elegantly curved roofs with low western eaves that greatly reduced the sense of bulk. Glazing also helped break up the mass, whilst offering a degree of transparency that communicated openness. Mid-range colours further softened the building’s intrusion onto the skyline.

The stature of the project meant a public enquiry was mandatory. However, it sailed through a traditionally lengthy process. The visually cohesive complex has added to, rather than detracted from Shell Green. It was completed on time, and won a RIBA award – the first industrial building to do so for 20 years.

The 1991 Urban Waste Water Treatment Directive required water companies to cease marine disposal by 31 December 1998. The planned processing centre would separate the solid content of the sludge from the water content. The liquid would then be sent for treatment, whilst the solid would be part used for agriculture and part incinerated. An incinerator is not a pretty thing. Tall and ugly, its working parts aren’t normally covered. So such a design was unlikely to win planning permission at any of the prospective sites in the Mersey Valley earmarked in our site-search carried out for a waste processing plant on behalf of our client, United Utilities. Options for the site were limited to the path of existing sewage pipes. The Mersey Valley is open and flat, and the proposed plant extremely large, and impossible to hide.

But whilst Shell Green was the preferred site for this process, the opposition from nearby housing, a third of a mile away, and nearby business units, just 300 metres away, was likely to be strong. The challenge was further increased by a particularly tight timeframe. Our task was to see if the process could be eased through innovative design.

We worked in tandem with process engineers to see if there were ways to cover the unsightly incineration element, aiming to avoid a rectilinear form, which was deemed inappropriate. Consequently the main achievement was to split the facility into its component parts, so the two main elements of the process, the dewatering and incineration plants, could be housed in discreet building envelopes linked by a smaller-scale element incorporating the odour control and control functions. The profile of the main building closely follows the height and profile of the incineration equipment. The plant is contained under a shallow curved roof which is repeated in a complementary way over the dewatering building. The curved roof results in much lower building eaves at the western end than the 30m at its apex, presenting significantly less apparent mass to the adjacent office buildings and housing beyond. In contrast to the predominantly rectilinear industrial buildings in Widnes, this design approach produces a softer building outline and helps its assimilation into the wider landscape of the Mersey Valley.

The functional separation of process streams in the incinerator building is accentuated visually by the articulation of the roof and walls. This helps reduce the apparent building bulk and scale when viewed close-to. A central element housing the electrostatic precipitators is partially roofed over but not enclosed, allowing glimpses of the process and views (north-south) through the buildings. The articulation of the roof and incorporation of high level glazing to the incinerator is important in breaking down the apparent bulk of the building when viewed from the surrounding residential and industrial area. The recesses in the main roof would also provide screened zones for small-scale external plant and equipment which would otherwise disrupt the clean lines of the roof.

Walls are glazed at upper levels and selectively at the lower level to open up views into the complex, providing an element of natural lighting as well as views through the building, relieving the bulk and mass at roof level. A base of architectural masonry with some limited glazing at the lower level reflects its proximity to the working processes surrounding the building. The wall element between the upper level glazing and lower masonry base is clad in metal-faced composite panels. This stratification of the elevations also helps to reduce apparent bulk and scale.

The ancillary buildings are treated in a complementary manner. The workshops and substation use gentle curved roofs to echo the form of the principle buildings and where appropriate, the same palette of external materials – glazing, masonry and cladding. External tanks and silos are fully or partially clad to form visually integrated local groupings and relate to the general building character.

The construction materials are compatible with a high quality industrial development and selected for their durability and low maintenance. The colours of the buildings, ancillary structures and silos are within the mid-tone range – silver greys and warm greys – which help assimilation of the complex into its surroundings: most importantly the typical north-western sky.

Separating the building’s structural support from the process plant meant that construction of both could take place at the same time. The project was completed within its deadline, despite the daunting process of a long and complicated public enquiry, mandatory with this type of structure. In the end the enquiry was swift and trouble-free, and the plant made it through the process without fuss. The visually cohesive complex has added to, rather than detracted from Shell Green. It won a RIBA award – the first industrial building to do so for 20 years.