St. Patrick’s Church Monkstown is approx. 150 years old, and the original building fabric is largely in place since the 1860’s. Over the years ad-hoc running repairs were carried out, however following the discovery of fragments of the cast-iron roof crestings on the adjoining ground, further detailed investigation revealed that many of the 1 metre high cast-iron finial units were unstable, and had in the past been tied together with lightweight galvanised straps, many of which had broken in severe wind conditions. The slating had also deteriorated through nail fatigue, and instead of replacement, many loose slates had been re-fixed using power-driven steel screws.
The Parish Committee appointed Conservation Architects to advise, and it was decided to re-slate and insulate the roof, which required the removal and repair of the main roof cast-iron ridge crestings, which were in 1.200mm lengths, each weighing approx. 500 kilograms. This required a detailed analysis of the fixings of the units to ensure that the roof structure and slating would not be damaged. This was achieved using a crane and cherry-picker, and the units were taken to Bushy Park Ironworks for repair and repainting.
The original slates were regrettably found to be largely unfit for re-use, due to the effects of double-fixings and nail fatigue which had enlarged the original nail-holes. The reslating work required the use of two contrasting slates to achieve the original striped effect, and also required that each of the Pennrhyn slates had to be double-chamfered on site to match the original design. The insertion of a vapour barrier below the insulation, and counter-battening the slates to install a vapour-permeable roofing underfelt, meant the careful design of all of the original abutment details. As there are 11 separate roofs, each detail had to be carefully considered. The original rainwater pipes installed on the surface of the side-aisle roofs were eliminated by installing leaded channels in the depth of the roof construction. Other detail improvements were achieved at the baptismal turret roof and at the apse, to enable the slates in these vulnerable locations to be securely fixed; and improved copper parapet gutters were installed at the baptismal turret and at the sacristy roof.
On completion of the re-slating of the main roof, the refurbished cast-iron finial crestings were re-installed, the re-assembly of the units being carefully carried out using the original techniques, modified so that the floral nails were extended to cope with the additional depth of the counter-battens, and an epoxy cement was used as a substitute for the original red lead.
With a comprehensive set of tender documents and details, pro-active relations between the building contractor and the design team, and active project management throughout the works, the project was completed exactly as budgeted.