Carrickfergus Castle

The client was looking for a pitched roof to be reinstalled in the Great Tower but needed some specialist help so contacted Paul, who lives south of Dublin, and had worked on the restoration of a number of historic buildings in the UK.

Based on Paul’s initial design for the oak frame, Carpenter Oak developed the scheme pre-tender, securing the project on the basis of our consultative approach with the design team and contractors, along with our enthusiasm and expertise.

Mixing modern software and traditional techniques

We worked closely with the main contractors, JPM Contractors, in order to get the detailed information we needed to design a frame for such an old building. 

The roof was not square in plan, there were no right angles and all the hips (where the timbers meet on a corner) were irregular. JPM used a point cloud survey which fires a laser around to get a perfect representation of what the 3D shape of this 800-year-old stone building was. It was also surveyed above and below the roof to link the whole thing together. This data was then used to create an accurate 3D CAD model of the ancient stone walls. Several bulges in the walls were identified in this 3D model which, had they not been spotted early on, could have resulted in a frame which would not have fitted. This data can also be kept as an important record of an ancient monument.

The frame itself was a simple and a functional design, as per the client’s requirements. The very irregular shape of the walls in plan resulted in a frame with every hip rafter (the sloping corner timbers) being unique, cut with different angles from the other seven.  This irregularity tested our expert carpenter Tom Kempton to the limit as he led the team cutting and erecting the frame. 

The client specified the use of Irish oak, so this was sourced from County Wicklow where some trees had been felled by Storm Ophelia in 2017. The frame was handcrafted in our Devon Yard and shipped over to the Northern Ireland site. 

The Carpenter Oak team was on site for two weeks in July 2019. They used timber pegs and the same jointing techniques that have been used since the medieval times to install the frame. 

The installation was seamless, thanks to the detailed point cloud survey – a frame of this complexity quite simply could not have been manufactured off-site without this level of information. There were a few complications such as squinch arches which made the installation tricky and there was no allowance for shuffling around the beams. This meant they had to go up in a certain order, and this wouldn’t have been possible without the digital survey. 

A public building with public interest

Being a public building this had a lot of interest from the public and the media (our Frame Designer Paul Slemmings featured in a BBC news video about it). We also had to provide a scale model of the frame so it could be shown to children in local schools and used as part of a display in the visitors centre.

This was a prestigious project and Carpenter Oak were proud to be involved in the preservation of this important monument that had apparently not had a pitched roof since Henry VIII was on the throne!

It went on to win the RSUA Regional Sustainability Award 2021:

“Replacement of the Great Keep roof with an appropriate open oak truss design has secured its integrity and allowed further interpretive and conservation works within the castle complex. The area beneath the roof is now a healthier environment for staff, visitors and historical artefacts.”

Photography: © Crown DfC Historic Environment Division