A visit to the King's College Chapel

The breathtaking vaulted ceiling is the largest of its kind in the world, completed between 1512 and 1515 by master mason John Wastell. From a structural engineer's viewpoint, this is where medieval ingenuity truly shines.

Imagine the forces at play here. Each of these delicate-looking stone fans, weighing many tonnes, is exerting a tremendous outward thrust. The key to managing these forces lies in a few critical elements:

1. The Vaulting Itself: The intricate pattern of ribs you see isn't just decorative. These ribs act like a series of arches, channelling the weight downwards and outwards. The spaces between them, the 'panels' or 'webs,' are filled with much lighter stone. Think of it like an incredibly complex, three-dimensional stone skeleton.

2. The Buttresses: If you look outside (or even at the massive stone piers along the walls inside), you'll see enormous buttresses. These are the external counter-forces, pushing back against the outward thrust of the vaults, preventing the walls from bulging out or collapsing. The cleverness here is how they are integrated into the overall design, appearing as elegant features rather than just brute supports.

3. The Pinnacles: The ornate pinnacles you see atop the buttresses aren't just for show either. Their weight adds to the downward force on the buttresses, increasing their effectiveness in counteracting the vault's thrust. It’s a beautifully balanced system.

4. The Stone: The primary material is limestone, carefully selected for its compressive strength. Each block was meticulously cut and shaped to fit perfectly. The precision required, without the aid of modern computers or cutting tools, is astounding.

5. The leaded timber Roof: that is the first line of defence against the external forces of nature, sheltering the stone roof from rain and elements, and granting the external pitched roof view of the building (and supporting the recent addition of PV panels, more details below).

From the chapel’s entrance, we followed our tour guide through the main hall, were we also had a brief risk and hazard brief before going up to the roof and vault, and from the hall we stepped through a small side door that leads to the narrow spiral staircase that leads to the roof and vaulted space.

At the roof, we learned from Patrick and Shane about the recent re-leading works and installation of PV panels providing a sustainable source of energy to the chapel, and we learned of the challenges theses modern interventions posed onto the design and construction of those additions, as the designers needed to figure a way to integrate and support those panels into the existing timber roof, and routing all the relevant utilities required for efficient performance.

 

In the vaulted space, we had the chance to appreciate the precise and extraordinary accuracy of the stone cutting and geometry of each block tying into the other and forming the whole of the vault. Considering the time at which this was built, one can only admire the genuineness and skill of the masons who carried out this work.

Over the stone vault, stands the timber roof, which consists of timber trusses -spanning across the width of the chapel and ending with arched timber columns that sit on top of the stone pillars and buttresses- and timber joists and rafters. The trusses are believed to be of oak trees.

Prior to the installation of the PV panels, an extensive structural assessment had been carried out to verify the structural integrity of the roof components and its capacity to accommodate the additional weight on top.


 

At the end of the tour, we learned about the college efforts towards decarbonization; some of the major activities towards zero carbon are the implementation of ground source heat pumps providing both heating and utility hot water, with the intention of expanding this project and installing more systems. In addition to the use of PV panels, LED lights.

The visit to this iconic chapel was a very interesting experience to all attendees and offered a unique learning opportunity and a glimpse to the past, to how things were done before we had all the fancy technology we have today. One can only appreciate the effort required to maintain and preserve such iconic fragile monuments and the immense planning and works carried in the background to offer a safe, sustainable and safe experience for the users.