Soaring timber columns create an impressive structure as part of the newly restored Clifford’s Tower in York, which was shortlisted for a 2022 Wood Award.
Clifford’s Tower, once the keep of York Castle, is a scheduled monument perched on a man-made motte. Until recently the remains of the English Heritage structure were little more than a hollowed-out shell. But a £5 million refurbishment project has brought life back to the bastion, opening up parts of the tower that have been off-limits since it was gutted by fire in 1684.
The works included installing aerial walkways to provide access to the first-floor rooms of the tower, while a freestanding roof deck provides spectacular 360-degree views across York. Marley’s non-slip timber decking, CitiDeck®, was used to help ensure the safety of visitors and to provide a natural and attractive surface.
Timber was ideally suited for the new structure due to its low-carbon impact and lightweight properties. It also offers longstanding durability and the low-maintenance needed for the structure’s 50-year design life.
The raised location, limited access, steep slopes, and irregular geometry at the site made construction of the tower challenging, but all timber components were designed so they could be lifted in and connected on the site, using concealed connections.
Non-slip decking fit for a king
Building the roof deck required careful planning, both to preserve the historic structure and to ensure the new elements were structurally sound. This meant building a completely new timber structure inside the tower.
Four enormous glulam columns were installed to provide support for the deck. They also form the basis for the internal walkways and staircases that access the upper levels of the tower.
The non-slip timber deck itself was constructed using Marley CitiDeck®. The decking was installed and carefully cut to a smooth curve following the line of the new metalwork guarding at the edge. There is also a large opening in the middle to allow visitors to look down to the floor of the keep. The boards were also used to create seating areas and a guard structure around the central opening.
An architect at Hugh Broughton Architects says: “We chose CitiDeck® because we needed an attractive and robust anti-slip timber decking for use in high-traffic public areas. We wanted a consistent appearance between the deck boards and the timber boards forming the sides to the benches and perimeter guarding, and CitiDeck® made that possible.
The Health and Safety Executive says flooring is considered to have a low slip potential if it achieves a pendulum test value (PTV) of at least 36. CitiDeck® has been extensively tested and found to have PTVs of 61 when wet and 73 when dry.
Sustainable non-slip timber decking
While a variety of decking products were considered, timber was chosen because of it’s strong sustainability credentials. Marley CitiDeck® is sourced from managed forests that are PEFC- or FSC-certified and, being timber, there are more options for recycling the board at the end of their usable life. For extra reassurance, CitiDeck® has the TDCA DeckMark and DeckMark Plus quality certification.
- Architect: Hugh Broughton Architects and Martin Ashley Architects
- Client: English Heritage
- Structural Engineer: Ramboll
- Main Contractor: Simpson (York)
- Joinery Company: Buckland Timber Ltd & Simpson (York)
- Quantity Surveyor: RNJ Partnership
- Glulam manufacturer/structural timber contractor: Buckland Timber
- Wood Supplier: Piveteau Bois, Buckland Timber and Marley
- Species: PEFC-certified European Redwood
- Location: York