Explore I Blog I Mending Bones - Shrewsbury Flaxmill Maltings by Tim Greensmith

21 August 2020

Shrewsbury Flaxmill Maltings was built in 1797 during the reign of George III. It must have been a terrifying sight, a five-storey behemoth looming over the medieval streets of Shrewsbury. Its internal gas lighting, giant smoking chimneys and sawtooth roof earned it the nickname ‘the dragon on the hill'.

The flaxmill was a piece of revolutionary engineering. It was the first building constructed using a structural system of cast-iron beams, posts and tie rods with jack arches, making it the first fireproof mill to be built. Cruciform columns which fork at the capital to support drive shafts and hog backed beams, fixed together using nuts and bolts just as we would today. Shallow brick jack arches span between the iron beams and the whole is bound together with delicate, wrought iron tie rods, like a giant house of cards. It was highly praised at the time of construction and now, 220 years on, it is considered one of the most important buildings of the industrial revolution.

By 1897, due to the popularity of cotton, the flax industry had collapsed, and the building was up for sale. It was bought by a local maltster and was skilfully converted into a maltings, giving the building its double-barrelled name. The maltings remained in use until 1986 when the buildings were once more put up for sale. A succession of failed attempts by the private sector led to a gradual decline in the condition of the buildings. In 2005 Historic England stepped in to save them for the nation.

The innovative design of the Main Mill may have set the trajectory for modern high-rise construction, but as with many pioneering projects, there were flaws that soon became evident and had to be ironed out in later buildings on the site. The Main Mill’s Achilles’ heel lies deep within its walls and beneath its very foundations.  Extensive embedded timber has rotted over time, causing the walls to split in two. In addition, settlement has led to tensile cracking in the tops of almost all the brittle cast-iron beams.

These hidden defects were carefully surveyed by specialists under the direction of FCBStudios’ conservation accredited architects and engineers. The final prognosis was dire, the only safe course was to erect an emergency propping to prevent progressive collapse. With a stay of execution secured, attention turned to a permanent repair.

A traditional like-for-like repair of the structure was considered, but the extent of opening-up required to access every repair would have led to the main elevations needing to be re-built. We turned to our innovative structural engineering friends at AKTII and Historic Englands' Conservation Engineering Team who together came up with the brilliant solution of knitting together the masonry around the fragile cast iron beams to provide robustness and additional capacity.

This repair strategy retained both the special character and re-utilised the embodied energy in the 200-year-old bricks and iron frame. Designs were developed to a high level of detail using advanced computer modelling, but the questions of buildability, safety, budget and programme could only be answered with a full-scale trial.

In 2016, Historic England commissioned an experienced heritage contractor and temporary works specialist to develop a step by step methodology to remove the rotten embedded timber which had brought the building to a state of imminent collapse. The trial took six months of adjustments and refinements to find the most efficient methodology. This allowed the project to be fully designed and billed producing several competitive tenders within time and budget. Time spent resolving big risk items before going to tender is a key lesson learnt.

The main contract comprising the structural repairs and reforming windows proceeded methodically over two years until finally the propping could be removed to reveal the blend of old and new in 2018. This was a big moment for the team and the local community. After 30 years of dereliction and false-starts, a new era was dawning.

With modern technology and engineering innovation applied, these heritage buildings are now ready to be fitted out for new uses. Another chapter in the story of the evolution of the world’s first iron-framed building.

Tim Greensmith

Tim Greensmith is a SPAB scholar and over the past decade has delivered a string of national and international award-winning Heritage Lottery Funded projects re-energising heritage buildings and returning them to use. He is the project architect for Shrewsbury Flaxmill Maltings, leading all phases of the conservation, regeneration and transformation project.

The building restoration of the Grade I listed Main Mill and Grade II listed Kiln at Shrewsbury Flaxmill Maltings will be complete in autumn 2021. Commercial tenants will be invited to occupy on the top four floors of the mill from this date.



Images

1. Coalbrookdale by Night by Philip James de Loutherbourg depicts industry in the Shrewsbury area and has come to symbolise the birth of the industrial revolution in the area.

2. Structural timber was embedded in the brick wall and had become rotten over time.

3. Original finish of the Main Mill’s cast iron column head(s)\, exposed in 2019 in preparation for fresh layers of fire-protective intumescent paint to be applied. (c) Historic England

4. Structural diagram of the iron frame to the mill (c) AKTII / Tie-rod diagram

5. Casting of new iron elements

6. Scaffolding and propping enshrouded the building while structural repairs took place.

7. The facade once structural repairs had been completed\, windows reformed and the scaffolding finally removed.

8. Internal view\, prior to work starting.

9. New uses for the Flaxmill will open the next chapter of the world's first iron-framed building. © Historic England

All images copyright FCBStudios unless otherwise stated.