In pictures: Dublin Cathedral’s roof restoration

St Patrick’s Cathedral’s biggest construction project in 150
years has involved a complex temporary works design.

Repairs to the roof of St Patrick’s Cathedral in Dublin have reached an important milestone with the completion of a vast scaffold and weather protection system for the 800-year-old building. The £8m conservation project began last September with the appointment of Clancy Construction as main contractor.

It follows storm damage four years ago, when high winds blew
slates off the roof leaving two holes large enough “to drive a Mini car
through”, in the words of the Very Reverend William Morton, dean of St Patrick’s.

It is the largest project at the cathedral since the
restoration by Benjamin Lee Guinness 150 years ago. The distinctive blue grey
slates used for the work will be sourced from the same slate mine in Wales as
those in the 1860s.

The scaffolding design took a year to plan. As tying into
the building was not possible, Clancy, scaffolding contractor Ainscaff and
scaffold supplier Layher designed a bespoke support structure.

“Clusters of beams were clamped to the walls, then fixed to
external support scaffolds to provide a base for further structural elements
which rise to support the temporary roof,” explains Ainscaff director Simon
Ainscough.

“The design effectively bridges – and, therefore, avoids
loading onto – lower roof areas which run alongside the nave, while helping to
ensure an important door access area remains open. At the same time, the
external support scaffold, which extends down to ground level, provides the
optimum structure for the installation of a material loading bay and access stair
system.”

The ‘bay-by-bay’ construction of the Layher temporary roof
structure meant that the limitations of only having one crane on site were
sufficient for the installation.  “As
each bay was craned into position and sheeted, it was then rolled along and
fixed to create space for the following frame,” says Ainscough.

The scaffold and temporary roof installation was completed
in four months by a team of 14 scaffolders. Almost 10km of scaffolding was used
and the temporary roof spans some 18m.

The restoration project will take around two years and the cathedral is expected to stay open throughout.