Norwich has more surviving undercrofts than any other city in the UK.
But what is an undercroft?
An undercroft, in the context of a building, typically refers to a often brick-lined and vaulted cellar or storage room beneath a building that is partially or completely below ground level. Typically these have been in place since the Medieval times!
Whilst historical landmarks throughout Norwich like the Bridewell, St Andrew’s Hall and the Castle all have undercrofts. The fascinating thing about Norwich undercrofts is that they weren’t just used for storage. The undercroft at The Guildhall, for example, was used as a prison, and later as a hiding place for Norwich’s valuable civic regalia during WW2.
There are several undercrofts across the city, but due to structural issues, many are being bricked up or filled in for safety reasons.
The structural design of an undercroft involves many considerations to ensure structural integrity, stability, and functionality. Here are some key aspects a structural engineer might consider when working on the undercroft of a building:
The undercrofts foundation must be designed to support the additional load imposed by the building above, as well as any dynamic loads from vehicles, equipment, or stored items.
The engineer needs to consider the soil conditions to determine the capacity of the existing foundation, if any is present at all!
Columns and walls in the undercroft must be designed to withstand the loads they will bear. This includes both the dead loads (permanent static loads) and live loads (temporary dynamic loads) associated with the intended use of the space.
Traditionally these are constructed from load bearing masonry, often vaulted or arched to be self stable. If modifications are required, often reinforced concrete or steel elements may be used to provide the necessary strength and durability.
Earth Retaining Structures:
If the undercroft is below ground level on one or more sides, retaining walls may be required to support the surrounding soil and prevent it from collapsing into the space.
The design of these retaining structures involves considerations of soil pressure, drainage, and stability.
Waterproofing and Drainage:
Since undercrofts are partially or fully below ground, preventing water ingress is crucial. Waterproofing measures, such as membrane systems and proper drainage, are essential to protect the structure from moisture-related issues. These are often one of the main deterioration mechanisms for existing structures.
In summary, the structural engineer plays a critical role in ensuring the undercrofts stability, safety, and functionality, taking into account a range of factors related to foundation design, load-bearing elements, earth retention and waterproofing. Being a local engineering consultancy in a city with numerous undercrofts, we are well versed with the intricacies of working with these existing historic structures.