My favourite retrofit? –  The Norman construction at Colchester Castle. 

With Civic Engineers supporting the upcoming NLA Retrofit Summit, our team is reflecting on their favourite retrofit projects. Instead of predictably talking about one of my projects, I thought long and hard about buildings that have meant something to me over my lifetime. 

I grew up with the beautiful (and underrated) County of Essex on my doorstep. Essex has some wonderful historic buildings including Colchester Castle, which was a regular for family outings. As a parent myself, I have re-visited this 11th century Norman keep with my own children. 

Colchester was the Roman capital of Britain. By the time the Norman’s had made it to Colchester the Romans were long gone but the remains of many of their buildings were left behind. This included the mighty Temple of Claudius. 

And the Normans spotted a retrofit opportunity. 

A typical Norman keep is located at the perimeter of a settlement; more or less square on plan; four storeys; with an entrance at first floor via external stairs. Think the White Tower at the Tower of London. But at Colchester that design was adapted to make use of the Roman temple structure found in place by the Normans. 

Firstly, location: 

The Castle is close to the centre of the city (yes Colchester is a city) not the perimeter. They were prepared to compromise on location to take advantage of an existing structure. They needed defences quickly. 

Questioning the need for a new building is a principle of sustainable design we now need to be asking. Why construct a new building when there may be an opportunity to reuse an existing structure on site or nearby? 

Next, foundations: 

Groundworks is a significant cost for any building. At Colchester, the robust Roman foundations were kept in place and extended as needed. A big saving in time, labour and materials. 

Today, new foundations are designed to higher factors of safety than the superstructure to deal with variability and risk of unknowns below ground. Understanding of existing foundations and adapting them for reuse is an approach I have adopted on projects resulting in savings in cost and materials. The Normans were at it a thousand years ago. 

Thirdly, re-use of materials: 

The Essex geology is good for clay to make bricks. But the Roman stone buildings, still largely in place around Colchester, were too good an opportunity to miss. The Normans reclaimed stone and reused it to construct the new keep walls. 

I now employ similar circular economy principles to my retrofit projects, identifying opportunities to reuse structure, either in situ, elsewhere in the building, or in other projects. 

So there it is, Colchester Castle. A great building which employed many of the retrofit and sustainability principles which are front and centre of my own building design work now. 

Though I expect the Norman’s approach was more out of necessity than anything else, reflecting on these historic periods, where reuse and lean design was needed, can help us today. Climate breakdown is the greatest challenge the human race has faced and looking back on previous times of crisis helps to develop strategies to deal with the emergency we find ourselves in today. 

Retrofit, reuse and circular economy principles are fundamental in reducing carbon emissions. I have had the opportunity to work with some great engineers and contribute to the collective recording of strategies, including for retrofit projects, in the IStructE Circular Economy and Reuse: Guidance for Designers.