Welsh Slate Helps All Souls from the End of an Era to a New One

The only surviving church by the Georgian/Regency architect John Nash is enjoying a new lease of life in its bicentenary, thanks to Welsh Slate.

All Souls Church, in the Harley Street Conservation Area of Marylebone, London, has been reroofed with 20” x 12” County-grade Penrhyn Heather Blue slates from Welsh Slate as part of a wholescale refurbishment of the iconic Grade I listed building.

Will Pryce

The first phase, to the external fabric, required a temporary roof and full scaffolding reaching to the top of the spire which now has ability to light up in any colour to suit the seasons and festivities. The scaffolding had to be engineered in great detail as the church occupies 100% of its ownership footprint.

The Welsh slates were installed over 240m² of the main nave roof, which has a pitch of 28°, using 38mm thick copper nails, and the flat roofs of the aisles, half of which had been covered in copper after the Second World War, were laid with 16 tonnes of lead, by roofing contractors Lead Roof Solutions for main contractor Quinn London.

The roof, which is hipped at the south-west end and incorporates a timber louvred structure for ventilation, is also fitted with several conservation rooflights which sit flush with the slates. To improve ventilation, the Welsh slates were counter-battened to raise the roof level, and to incorporate this, secret gutters were used at the abutments and around the rooflights. A slate and a half were employed on all abutments, and ridges and hips were finished with a lead roll and wing detail.

Although the church was built in 1824, it was damaged by bombing in 1940 and the roof was renewed during the post-war rebuild, so the Welsh slates that were most recently replaced were likely to be about 75 years old, if they were installed new.

Specifiers Matthew Lloyd Architects, who specialise in historic and heritage buildings and are a conservation-accredited practice, have specified Welsh Slate on numerous occasions for a variety of church and secular buildings.

Director Alex Sherratt explained that during All Souls’ quinquennial inspection in 2019 it was identified that the slate roof and remaining areas of copper roof had numerous defects and were near the end of their serviceable lives. In addition, there were a number of stonework and other issues which required attention. The client, the parochial church council, therefore decided to carry out a single conservation project on the entire external building fabric, to leave it in the best condition possible for its bicentenary in 2024.

The conservation work required the use of traditional materials, consistent with those that would have been used on the original building in 1824. So, as the project largely consisted of like-for-like conservation work, Westminster deemed that planning permission was not necessary for anything other than the re-lighting of the spire, which was a component part of the project. The project was also subject to permission from the Diocese of London, who were supportive of the proposals. Consultees also included the Georgian Group and Historic England.

Alex said, “Welsh Slate was the natural choice, as the church would always have been roofed in Welsh Slate from its original construction in 1824. Re-roofing the nave in Welsh Slate was possibly the most significant element of the project, as it prevents problems with ongoing water ingress, and contributes greatly to the longevity of the roof, and the church as a whole. "

“The church is an iconic building, occupying a key position on Regent Street, and is highly visible from the surrounding streets, therefore the aesthetic qualities of Welsh Slate were a major consideration. The roof at All Souls is overlooked from BBC Broadcasting House and is often used as the backdrop for filming current affairs programmes from the studios and rooftop terraces.”

The aesthetics of Welsh Slate were not the only reasons for specification, however.

Alex said, “Across the project, British materials were sourced and specified wherever possible, to ensure that historically authentic materials were being used, to support local industries and to minimise the need for transport."

“One of the driving factors behind the project was the need to extend the lifespan of the building as far as possible by using appropriately durable materials. The 100+ years of useful life offered by Welsh Slate was an important factor in the selection of Welsh Slate for a roofing material at All Souls. The fact that the material is 100% natural and has a low carbon footprint were also important considerations in the specification of Welsh Slate.”

He added, “Welsh Slate was specified for its strength and durability, and for the aesthetic qualities given by its purple hue. Physical performance of the slates was one of the key drivers for the project, and the Penrhyn slates were selected for their particular suitability to the roof at All Souls. The combination of Welsh Slate and lead provides authentic and robust weathering details throughout."

“The client body recognises the significance of the church, and their responsibility as custodians of a significant heritage asset to use the best possible materials in the repair of the building. They are totally committed to the use of appropriate materials and are delighted by the result.”

Andy Mead of Lead Roof Solutions said, “Although All Souls Church is a very significant building, the actual reroofing project was straightforward. We have used Welsh Slate on many a project and they are always a joy to work with.”

Phase Two of the refurbishment of the church, which attracts 1,500 visitors per week, will focus on its interior.