Welsh Slates Score Over a Century at a Private School
Howell’s School in Wales has a new roof thanks to Welsh Slate.
The complex reroof, with Welsh Slate, of a Grade II* listed school building, after at least a century, has won the contractors a place in the finals of specialist national awards.
Camilleri Roofing’s year-long work on Howell’s School, an independent day school in Cardiff for girls aged three to 18 and boys aged 16 to 18, involved more than 1,000m2 of Welsh Slate’s Penrhyn Heather Blue County-grade slates in 600mm x 300mm and 455mm x 250mm sizes.
These were complemented by bands of Vermont Unfading Green slates in 600mm x 300mm and 500mm x 250mm sizes. These were used as standard rectangles just below the ridge line and on the eaves, and as arrowheads creating the illusion of hexagons, around dormer windows and chimneys.
Camilleri’s work on phase 1 of the external fabric repair project, on the school’s main entrance building and a clock tower, has won the Welsh company a shortlisting in the roof slating category of the 2025 UK Roofing Awards organised by the NFRC.
Although the school was built in 1858, a substantial part of it was damaged by a major fire in 1920, so it is likely the Welsh Slates had been on the roof since then, 105 years ago. The Unfading Green ones from New England Slate quarries are produced from slate beds laid down in the same Cambrian era as Welsh Slate’s Penrhyn slate, so match their otherwise unrivalled quality.
Specified on a like-for-like basis by 310studio architects for specialist school refurbishment contractor Eden London, they were installed throughout the school year, with the Girls Day School Trust building live and functioning fully for most of the contract period.
The multi-faceted roof build up included a vapour control layer, insulation, counter battens, traditional felt, battens and slating, in addition to complex supplementary detailing such as clay slotted roll-top ridge tiles with fleur-de-lys inserts (the ridge tiles mortar bedded and mechanically fixed, along with a continuous ventilated ridge system), renewal of all lead flashings, cappings and detailing and bat mitigation/access measures.
Camilleri senior quantity surveyor Simon Bailey said: “In addition to the complex roof build up and the logistics of operating over a live school, we also had the further complication of feature bands in the existing slate roof, which were to be replicated. These feature bands used two different types of slate (Penrhyn Heather Blue and Vermont green) in patterns of standard rectangular courses and arrowhead courses.
“A very careful survey of the existing slates was therefore undertaken, to create an accurate record of the existing roof and ensure that the historic pattern was retained. However, due to issues with the original roof design, the ornamental courses of the existing roof did not line through on adjacent elevations. The architect required us to retain the existing pattern but achieve continuous lines around the roof, which was successfully achieved. We also had the added complication of the same slate arrangement on a tower roof but in a smaller slate size.”
He added: “Workmanship is an absolute key factor in any roofing project, but a 165-year-old (live) private school with a specification as complex as this, under the close scrutiny of Cadw, made attention to detail so much more important. The historic nature and importance of the property demanded a suitably experienced and qualified site team, to ensure the absolute best possible result. Our team therefore consisted of the foreman responsible for our last NFRC award-winning slate project, leading a four-man team with over 62 years of experience between them.”
Three young Camilleri operatives who were undertaking their Roof Slating and Tiling NVQ Level 2 qualifications at the time, also worked on the project at various stages.
“The project provided a perfect opportunity for each to display their natural slating abilities, with all three able to work with such a high-quality slate,” said Simon.
“Work of the utmost quality was required from the outset and the battening was a very careful process, due to the requirement for the ornamental slate bands to line through on adjacent elevations.”
310 Studio Architects said: “The roof, made of beautiful Heather Blue Welsh slate with horizontal banding in green, serves as the building’s first line of defense against the unforgiving Welsh weather! Through testing and liaison with slate experts, it was determined that the existing slates were in excess of their usable life and would be replaced. The opportunity to introduce an ultrafine layer of high performance insulation, the same insulation that has been used by Nasa on its rockets, was taken to improve the thermal performance of the roof without negatively impacting the external appearance or raising the ridge line of the roof. This ensured that the restoration was entirely in keeping with its historic appearance whilst reducing the carbon emissions of the school overall.”
A quantity of sound slates removed from the original roof was set aside for the school to service any future repairs of remaining original roofs and to use in the students’ Victorian term project. All other usable salvaged slates were transferred to salvage merchants, with the proceeds used to help offset the cost of the project.
The awards finals take place on 9th May.