Shredded Wheat Factory, Welwyn Garden City

Alterations and bold interventions are needed to allow this highly functional building to serve a new and different purpose. The quality of the concrete has been found to be variable with significant issues of decay, corrosion and spalling which need a variety of strategies for repair and lifespan prolongation.

The silo buildings are extraordinary but challenging to convert to alternative use. We have developed a structural concept for doing this with the architect to allow planning permission for a ‘competitive socialising’ venue. This will see the silos themselves converted into a climbing centre with other activities such as indoor skydiving a possibility. The top of the silo building has a single-story space which formerly housed grain delivery conveyors and chutes, and this will be converted to a restaurant and bar, which will be extended by adding a floor below within the silos, and opening up some of the walls to create a series of intimate spaces.

The Boiler House and Wheat Elevator will be refurbished to provide entrances, a new brewery tap bar, back of house and office space for rental. The whole complex will be served by a new external stair. 

We undertook a detailed appraisal of the structures to understand their form and condition, involving extensive investigations and testing. While the form of the structures is highly unusual, we were able to show that they were basically sound and well-conceived. Having been built for industrial use they have significant spare capacity which we are harnessing to allow major modifications without the need for major strengthening. The buildings suffer from two significant issues – the presence of asbestos bitumen waterproofing on the outside of the silos, and low cover to reinforcement, resulting in reinforcement corrosion and spalling of the concrete. We have developed a strategy for removing the asbestos and then carefully investigating and remediating the concrete, followed by a programme of external corrosion inhibitors and waterproofing that should secure the future of the building for many years to come.

So that workers could get to the site the station footbridge was progressively extended across the expanding railway sidings that served the factory. These sidings are no longer in use so they are to be removed to allow the whole site to be developed. The footbridge penetrates deep into the site, so to allow efficient development it needs to be shortened and a new stair constructed to link it to ground level. In doing this the opportunity is being taken to add a lift and incorporate a bridge level viewing platform with small retail unit below.

We have been providing Structural Engineering design of the demolition and design for the new lift, stair and viewing platform structure. We are acting as the Client’s Responsible Engineer (Design) (CRE-D) for the design of the alterations to Network Rail’s asset. We have prepared a submission for ‘Form A’ (Design concept) for submission to Network Rail.

The bridge has been altered and extended many times since the station was first constructed in the 1920s, as Welwyn Garden City started to be built. Our detailed historic analysis showed that the part of the bridge to be removed was also the last to be added, so that its removal could be justified to have no impact on the remaining structure, which had previously stood in this state. This has been presented in a series of drawings which explain the development of the structure and illustrate its structural action.