Installing two 6m flagpoles at Caerphilly Castle in Wales

Built in the 13th Century, Caerphilly Castle is the largest castle in Wales. Further, it is second only to Windsor Castle in the whole of Britain. Here, massive walls, towers and gatehouses were combined with sprawling water defences to cover a total of 30 acres.

Cadw – the historic environment service of the Welsh Government – have undertaken a significant programme of restoration at Caerphilly Castle. As part of this, Harrison’s were engaged to replace the two flagpoles on the iconic North-East and South-East towers.

Initially we ran a number of wind loading calculations to confirm the right design and stiffness for the flagpoles. We also had to define the appropriate size of bracket fixings. This was based on the elevation of the poles and the typical wind velocity for this location.

As the castle is a Grade-I listed building, special care had to be taken when installing the wall-mounted brackets. The key consideration for the installation of these flagpoles was to ensure that any connection into the fabric of the towers was exclusively into the mortar and not the stone.

Being unable to fix into the stone was a key element of the project solution. Working with a random pattern of mortar joints made the design of the bracket critical too. Harrison’s achieved this by designing a back plate that could allow for the random pattern. We also ran further structural calculations to ensure the random fixing patterns were correctly spaced. They also had to be to the correct depth to offer the correct support to the poles.