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17 August 2021

One of two unique cast iron churches in Liverpool is enjoying a new lease of life after a second phase of reroofing has been completed with Penrhyn Heather Blue slates from Welsh Slate.

The unique patent slate roofing project will help safeguard the Grade 1 listed St George’s Church in Everton which is on the Heritage at Risk register.

The church, which was built in 1814, is one of only two remaining world-renowned cast iron frame churches, both in Liverpool, the other being the 1815 St Michael’s in the Hamlet, Aigburth, otherwise known as the “Pink Church”.

Both buildings were designed and built by Mersey Iron Foundry owner John Cragg and the accountant-turned-architect Thomas Rickman. They developed a novel system to prefabricate church buildings and patented the iron and slate construction details.

The Phase Two reroof comprised large “modular” 20mm riven slabs of Welsh Slate’s Penrhyn Heather Blue slates ranging in size from 750mm x 850mm to 1,450mm x 850mm, employing a single-lap and laid almost flat, at a very low pitch of 7˚.

These were originally pinned onto the deep cast iron rafters set onto a hessian and putty sealant, employing an overlapping protective capping slate at all butt joints. A second ‘sarking’ layer of slate was employed, resting on the lower lip of the iron rafters, and these formed the underside of the ceiling. This created a cavity between the two layers of slate, effectively forming a very early rainscreen system.

Described by English Heritage as one of the earliest and most thorough uses of industrial materials in a major building, the churches are two of the first, and only remaining examples, of prefabricated and modular architecture in the world, hence their Grade I listing. The development of this cast iron architecture is believed to have paved the way for multi-storey framed buildings and ultimately the skyscraper.

Finlason Partnership Ltd (FPL), specialists in the restoration of historic buildings, were appointed as church architects for both churches, and are overseeing a series of repair works valued at more than £1.25 million. These tackle almost every aspect – roofs, towers, re-pointing, window repairs, internal redecoration and heating systems.

The unique, almost flat patent slate roof at St George’s had suffered from continual water ingress following the breakdown of the “sealing putty” and damage to the cast iron structure and decay had reached a dangerous state. Investigation by FPL highlighted the need for modern detailed design to respect the historic fabric and the original principles of the iron founder and architect.

Due to financial limitations, FPL proposed a two-phase strategy for replacing the roof, the first phase focusing on the nave roof which was in the worst condition, and the second phase reinstating the chancel and four porch roofs.

FPL designed a solution to the inherent faults (primarily, the putty degrading) and Phase One completed in June 2015. The nave was reroofed with a complete new treated timber substructure incorporating drainage zones, insulation and a new inner waterproof membrane with timber members supporting the slate panels.

The new overlapping slate panel detailing, associated joinery and metalwork was developed in close collaboration with Welsh Slate to respect the original intentions and aesthetic but with improved weathering provided by a special sarking layer and improved ventilation.

Phase One sub-contractors RoofAbility employed a modern system of stainless steel fabricated clips and fixings designed by FPL to support the load of the slate and resist movement.

They used a variety of Welsh Slate’s Penrhyn Heather Blue 20mm riven slates, ranging from 1,350mm x 950mm to 650mm x 200mm, as the capping slates, over 300m2 of one half of the roof. The Welsh slates on the other half were re-used and those which could not be re-used were recycled.

FPL then helped the church to secure a further £230,000 of funding to undertake the Phase Two reroof which was carried out by Manchester-based Mather and Ellis stonemasons. This phase saw the replacement of the remaining roofs – those at low level to the four corner porches and the chancel – employing similar construction details as devised for Phase One.

Mather & Ellis took almost nine months to lay the 75m2 of new slates onto the timber rafters with felt under. Additional timber noggins were added between the rafters to form a grid and ensure each slate was picked up on all four edges.

The slates were fixed with bespoke stainless steel brackets which hooked under the front edge and were screwed down to the top timber grid underneath. Expanding foam tape was then used to seal the slate at the top edge. Perps were made weathertight with a narrow slate slip or cover slate.

Phil Duerden of Mather & Ellis said:

“Access was fairly easy, through an old gate opening onto St Domingo Road, but the project was very challenging to complete. The roof is an unusually low pitch and the slates are unusually large, plus the jointing pattern is unusual in that the perp joints all line up, rather than being staggered as per a traditional roof.

“The roof system required hundreds of hours of labour to get up on and installed perfectly level. The slates themselves weighed over 100kg each and each one had to be physically manhandled into position, up a pitched roof, without breaking any of the extremely large slate pieces.”

FPL maintains that while St George’s is widely acclaimed as the world’s first ‘iron’ church it would be more fitting to be known as the ‘Iron AND Slate’ church as it is not only an influential and important piece of architecture due to its use of cast iron but integral to this was the widespread use of slate in this composite construction.

Conservation-accredited architect and managing director of the Finlason Partnership, Alex Finlason said:

“The work at St George’s Church is considered an exemplary project which has expanded the industry’s knowledge on historic roofing techniques and is a template for the training of slate roof professionals.”

Work outstanding includes repairs to the lead on the tower roof, masonry, further stone repairs to the window surrounds/tracery and to the stained-glass.


Conservation-accredited architect and managing director of the Finlason Partnership, Alex Finlason, said:

“With first-class early cooperation, prior to the start on site by Mather & Ellis, appropriately-sized and quality blocks of slate were selected in the Penrhyn quarry ready for cutting to size to create the wonderfully textured Heather Blue hand-riven 22mm slate panels that characterise this beautiful roof.

“This extremely challenging project was completed on budget and within the time constraints. As conservation-accredited architects, we are expert in the use of Welsh slate and cast iron in buildings but the support given by Welsh Slate on this project proved invaluable to reconstructing these unique roofs for future generations.”

He added:

“The only unfortunate thing is that, located at the highest point in a 50-mile radius, only the seagulls get to see the new roof of this fine historic building. That is apart from the church wardens who retrieve the many footballs that come to rest on the roofs from over-enthusiastic locals. Even this aspect was considered, by the ‘doubling-up’ of the supporting structure to prevent the cracking of slate panels under foot.”

Phil Duerden of Mather & Ellis said:

“The large slate sheets matched the dimensions of the originals exactly, and also the colour and consistency of the nave roof done in a previous phase of work. The new roof panels should ensure the roof remains watertight for many years to come.”

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