With a unique history stretching back to 900BC, Flat Holm is home to a tapestry of heritage monuments. Under a multi-phased project, funded by The National Lottery Heritage Fund, Cardiff Council orchestrated a series of works to restore two of its iconic buildings – the cholera and isolation hospital and fog horn station.

Situated in the Severn Estuary, the vital preservation work fits into Cardiff Council’s broader vision to regenerate the island and upgrade its infrastructure to strengthen its position as a top tourist attraction in the UK.

With extensive expertise in supporting complex heritage projects, our experts were appointed as the multidisciplinary Principal Designer during RIBA Stage 3, providing support across structural engineering, architecture, building surveying, contract administration and procurement. From protecting historical value to navigating ecological risks and devising a seamless logistical strategy for construction, we worked closely with the project team to create a resilient design to restore these heritage buildings – ensuring visitors can continue to explore these special historical wonders for years to come.

Client

  • Cardiff Council

Project Status

  • Complete

Location

  • Flat Holm, Wales
This project has allowed us to advance our vision for preserving Flat Holm’s built heritage and making it accessible to the public, giving visitors the opportunity to experience the island’s fascinating history first-hand. Despite the challenging location and timescales, WSP’s team successfully delivered a demanding programme, resulting in the preservation of two significant heritage buildings that were previously at risk. Their work ensures these structures can be enjoyed by future generations.

Key achievements

Size of cholera and isolation hospital (m2)
250
Size of fog horn station (m2)
125

A walk through time

A key aspect of the work was protecting and preserving each building’s historic character, aligning with UK Government heritage requirements. This involved cautiously considering the cholera and isolation hospital’s status as a Scheduled Ancient Monument and the fog horn station’s classification as a listed building. We conducted comprehensive assessments on the existing structures, including roofs, walls and chimneys, to determine all components needing repair and stabilisation to prevent further damage.

Our experts worked closely with Cadw and Heritage Recording Services Wales to conduct samples and identify the materials requiring replacement to ensure these could be procured on a like-for-like basis – allowing the original architecture to be retained. We also designed solutions to reinforce the existing structure, including waterproofing and propping, to make sure the buildings were structurally fit-for-purpose for visitors to enter and explore.

We also worked closely with Cadw, Trinity House and Cardiff Council from the start to prepare a compliant scaffolding design, which included the development of a scaffolding method statement. This early collaboration helped streamline construction planning and prevented further damage to the historic buildings, while providing teams with safe, effective access for any necessary work.

In-body 1

Before and after of the fog horn station

Protecting local life

As a Site of Special Scientific Interest (SSSI), there were strict ecological requirements to follow to prevent impacts to protected plants and animals inhabiting the island. A full environmental assessment was completed to understand how construction activities, vessel movements and material handling could affect protected species.

One of the most significant challenges was navigating a breeding colony of more than 4,000 lesser black backed gulls. These birds are legally protected, so our specialists worked closely with the project team to ensure the construction programme considered this with specific attention to their nesting season, adapting access routes, sequencing noisy activities and implementing stringent biosecurity controls for any vessels landing on the island to look after protected colonies.

We also assessed vegetation, mosses and lichen growing on surfaces earmarked for repair, checking for any rare or protected species and determining whether they required relocation.

In-body 2

Carefully mapping a logistical route

Given the island is only accessible by boat, every worker, tool and material had to be precisely coordinated in consideration of narrow tidal windows, vessel availability and specific procurement timelines.

Specialist vessels were booked months in advance, and all deliveries from heavy plant to flat pack accommodation, were timed to land exactly when the team needed to use them. This level of planning meant the works progressed through a single weather window, avoiding delays that could have pushed activities into the following year.

Meet our Visioneers

Richard Wilks, Technical Director at WSP in the UK and Ireland, led our multidisciplinary team from the early design stages of the project through to its completion in 2025. He has extensive experience delivering complex projects across various sectors, including being a technical advisor to Velindre Health Trust and others to support major healthcare projects in the UK, leading a multidisciplinary team to refurbish Pentwyn Leisure Centre and supporting the delivery of Passivhaus primary and secondary schools in Wales.

Restoring these two iconic buildings on Flat Holm demanded strong teamwork and precise planning. We’re proud to have supported Cardiff Council in revitalising these integral pieces of the island’s story, so people can continue to experience its intriguing and unique history.

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