PATENT SLATE ROOFING HELPS BRING UNIQUE CHURCH BACK FROM THE BRINK
14 July 2021
Work is due to start this month on the second phase of a unique patent slate roofing project which will safeguard a Grade 1-listed pioneering building currently on the Heritage at Risk register.
The project is the re-roofing of the 1814 St George’s Church in Everton, one of only two remaining world-renowned cast iron 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 roofing system for Phase Two comprises 75m2 of large “modular” 20mm riven slabs of Welsh Slate 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, they 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.
Specialists in the restoration of historic buildings, Finlason Partnership Ltd (FPL) is appointed as church architects for both of the cast iron churches, and is completing 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 patented, almost flat slate roof at St George’s had suffered from continual water ingress 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 St George’s roof, the first phase focusing on the nave roof which was in the worst condition, and the second phase reinstating the remainder – 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 (pictured right) 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.
Specialist Chester-based sub-contractors RoofAbility carried out the highly unusual slating. A modern system of stainless steel fabricated clips and fixings into the new timber support system was designed by FPL to support the load of the slate and resist movement.
RoofAbility used a variety of Welsh Slate’s Penrhyn Heather Blue 20mm riven slates – 1,350mm x 950mm, 700mm and 650mm, and 950mm, 700mm and 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.
Roofer Stephen Turner said:
“The project was very challenging as we had not done this type of reroof before. Installing the slates was particularly so as handling their size and weight had to be a two-man job. Added to this were the stainless steel brackets that each had to be bent for the individual size and thickness of the slates.
“The job was also difficult because of access to the church and getting the new slate to the roof level, with weather also a factor as we were so high up in Liverpool. But the Welsh slates performed excellently.”
FPL then helped the church to successfully secure a further £230,000 of funding to undertake Phase Two, the contract for which has been awarded to Manchester-based Mather and Ellis stonemasons. This phase will see the replacement of the remaining roofs (south-west porch pictured left) employing similar construction details as devised for Phase One.
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.
Videos on the reroofing of St George’s nave are available to view at www.stoneroof.org.uk/historic/Historic_Roofs/Everton
