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Manufacturer replacesunique slating system at the famous St George's Church.

One of twounique cast iron churches in Liverpool is enjoying a new lease of life after asecond phase of reroofing has been completed with Penrhyn Heather Blue slatesfrom Welsh Slate.

The unique patentslate roofing project will help safeguard the Grade 1 listed St George's Church in Everton which is on the Heritage atRisk register.

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

Both buildingswere designed and built by Mersey Iron Foundry owner John Cragg and theaccountant-turned-architect Thomas Rickman. They developed a novel system toprefabricate church buildings and patented the iron and slate constructiondetails.

The Phase Two reroof comprised large “modular” 20mm rivenslabs of Welsh Slate's Penrhyn Heather Blue slates ranging in size from 750mm x850mm to 1,450mm x 850mm, employing a single-lap and laid almost flat, at avery low pitch of 7˚.

These wereoriginally pinned onto the deep cast iron rafters set onto a hessian and puttysealant, employing an overlapping protective capping slate at all butt joints.A second 'sarking' layer of slate was employed, resting on the lower lip of theiron rafters, and these formed the underside of the ceiling. This created acavity between the two layers of slate, effectively forming a very earlyrainscreen system. 

Described byEnglish Heritage as one of the earliest and most thorough uses of industrial materialsin a major building, the churches are two of the first, and only remainingexamples, of prefabricated and modular architecture in the world, hence theirGrade I listing. The development of this cast iron architecture is believed tohave paved the way for multi-storey framed buildings and ultimately theskyscraper.

FinlasonPartnership Ltd (FPL), specialists in the restoration of historic buildings, wereappointed as church architects for both churches, and are overseeing a seriesof repair works valued at more than £1.25 million. These tackle almost everyaspect - roofs, towers, re-pointing, window repairs, internal redecoration andheating systems.

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

Due tofinancial limitations, FPL proposed a two-phase strategy for replacing theroof, the first phase focusing on the nave roof which was in the worstcondition, and the second phase reinstating the chancel and four porchroofs. 

FPL designed asolution to the inherent faults (primarily, the putty degrading) and Phase Onecompleted in June 2015. The nave was reroofed with a complete new treatedtimber substructure incorporating drainage zones, insulation and a new innerwaterproof membrane with timber members supporting the slate panels. 

The newoverlapping slate panel detailing, associated joinery and metalwork wasdeveloped in close collaboration with Welsh Slate to respect the originalintentions and aesthetic but with improved weathering provided by a specialsarking layer and improved ventilation.

Phase Onesub-contractors RoofAbility employed a modern system of stainless steelfabricated clips and fixings designed by FPL to support the load of the slateand resist movement. 

They used avariety of Welsh Slate's Penrhyn Heather Blue 20mm riven slates, ranging from 1,350mmx 950mm to 650mm x 200mm, as the capping slates, over 300m2 of onehalf of the roof. The Welsh slates on the other half were re-used and thosewhich could not be re-used were recycled.

FPL then helpedthe church to secure a further £230,000 of funding to undertake the Phase Two reroofwhich was carried out by Manchester-based Mather and Ellis stonemasons. Thisphase saw the replacement of the remaining roofs - those at low level to thefour corner porches and the chancel - employing similar construction details asdevised for Phase One.

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

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

Phil Duerden ofMather & Ellis said: “Access was fairly easy, through an old gate openingonto St Domingo Road, but the project was very challenging to complete. Theroof is an unusually low pitch and the slates are unusually large, plus thejointing pattern is unusual in that the perp joints all line up, rather thanbeing staggered as per a traditional roof.

“The roofsystem required hundreds of hours of labour to get up on and installedperfectly level. The slates themselves weighed over 100kg each and each one hadto be physically manhandled into position, up a pitched roof, without breakingany of the extremely large slate pieces.

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

Conservation-accreditedarchitect 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 inthe Penrhyn quarry ready for cutting to size to create the wonderfully texturedHeather Blue hand-riven 22mm slate panels that characterise this beautifulroof.

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

He added: “Theonly unfortunate thing is that, located at the highest point in a 50-mileradius, only the seagulls get to see the new roof of this fine historicbuilding. That is apart from the church wardens who retrieve the many footballsthat come to rest on the roofs from over-enthusiastic locals. Even this aspectwas considered, by the 'doubling-up' of the supporting structure to prevent thecracking of slate panels under foot.”

FPL maintainsthat while St George's is widely acclaimed as the world's first 'iron' churchit would be more fitting to be known as the 'Iron AND Slate' church as it isnot only an influential and important piece of architecture due to its use ofcast iron but integral to this was the widespread use of slate in thiscomposite construction.

“The work at StGeorge's Church is considered an exemplary project which has expanded the industry'sknowledge on historic roofing techniques and is a template for the training ofslate roof professionals,” said Alex.

Workoutstanding includes repairs to the lead on the tower roof, masonry, furtherstone repairs to the window surrounds/tracery and to the stained-glass.


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