How rebuilt cathedral could look
Architect Sir MILES WARREN believes it is time to rebuild Christ Church Cathedral according to George Gilbert Scott's original design in timber. Here, he surveys the building's history and considers how it might be done.
When considering how the Christchurch Cathedral might be rebuilt, it is worth reviewing the process of its design and building. In 1859 James Edward Fitzgerald, the provinces' emigration agent in London, was asked to have preliminary discussions with George Gilbert Scott for the design of the cathedral.
Scott was then England's pre-eminent gothic revival architect and was later to design some of London's most important civic buildings.
Scott had heard of the disastrous Wellington earthquake, which must have been an 8 or more on the Richter scale. He was aware that there were few stonemasons in New Zealand but plenty of good timber.
His first design was in the traditional form of a cross with nave, side aisles, transepts and choir to be built with external walls of stone but with all the rest of the structure, nave, columns, clerestory and roof in timber.
If the interior structure had been built in timber with columns in one length full height the Cathedral would probably be still standing today, as does the timber St Michaels and All Angels and the wooden columns and roof of Knox Church.
The stone cathedral
The first Bishop Harper insisted that the cathedral be built in stone. By this time the Lyttelton tunnel had been built and stone and stonemasons were available. Scott was instructed to redesign the cathedral in stone with stone columns, arches and clerestory and stone arches at the crossing of the nave and transepts.
The stone columns supported the great weight of the stone arches and clerestory.
The timber structure
It is now time to return to Scott's first design - that is to rebuild and earthquake strengthen most of the exterior stone walls including the whole of the iconic west front, the side aisles and apse up to their full height; but with the clerestory and the high gables of the transepts only in timber.
The whole of the interior structure, nave columns, arches, clerestory and roof would be rebuilt employing today's most advanced structural design in laminated timber, all lightweight and most importantly earthquake proof.
Curved arches would fan up from the columns to the apex of the roof similar in form to the ribs of late perpendicular gothic cathedrals. A beautiful light, open and original space would be created.
The great New Zealand tradition of wooden gothic, best exemplified by St Mary's Pro Cathedral in Auckland would be continued.
One of the valid criticisms of the Cathedral was that the congregation in the side aisles was separated both visually and acoustically from the nave by the close spaced large stone columns and their arches.
With the proposed lightweight timber structure, every second column in the nave would be deleted and the lengthwise arches lifted above the side aisle roofs thereby uniting the side aisles and nave into one great space, both visually and acoustically.
Similarly the four large stone columns supporting the stone arches of the crossing, which effectively confined the congregation to the nave, would be replaced with slender timber columns and arches thereby joining the transepts spatially to the nave.
The exterior stone walls would be strengthened by removing the interior limestone facings and in stages constructing reinforced concrete walls bonded to the remaining and rebuilt exterior basalt either by an epoxy type glue or by drilling and inserting steel rods. This is a well-proven and costed technique. The west walls of the side aisles and transepts were strengthened in this manner during the early earthquake strengthening. The inside walls would be best plastered with an Oamaru stone textured finish.
The limestone window surrounds and mullions of the side aisles which have mostly come apart at the joints would be fully restored.
The new timber structure
The main image on this page illustrates the full length of the nave, now three bays instead of six, the transepts and the one bay of the choir. From slender columns arches rise to the top of the clerestory and fan up to the roof of the nave.
The apparent height of the nave is increased by the removal of the heavy tie beam and struts of the nave trusses. Nave, side aisles and transepts become one great space.
The illustration above shows the cathedral looking east to the choir and apse, with the full width of the combined nave and side aisles further extended with the transepts.
The splendid stained glass windows of the side aisles, the north transept and the apse were removed, restored and replaced just before the earthquakes. After the first earthquake all the stained glass was again removed and is now held in store ready to be reinstated. The stained glass of the west rose window had not been removed before the February earthquake and was smashed beyond repair. The stained glass, one of the treasures of the Cathedral, would be restored, so would the "green" glass of the clerestory windows.
The beautiful wood work of the reredos behind the high altar and the side chapel in the south transept, standing against relatively undamaged walls would be fully restored. The stone pulpit, architect Mountfort's superb design, was badly damaged by stone falling from the transept arches. Hopefully it can be restored.
Within the restored exterior walls, a new cathedral is created, one great space higher and lighter, architecturally and structurally more innovative continuing the great tradition of New Zealand timber gothic.
The tower is an integral essential element of the cathedral. Without it the cathedral would appear to be a relatively small building, too small to form the centrepiece of the square. The Cathedral and tower were sited forward into the square to command the length of Colombo St.
Before the earthquakes, the tower was next on the list to be strengthened. Its walls were 1200mm thick, well-built basalt on the outside, brick on the inside and unknown rubble between. Its lower levels appeared to be well buttressed. The top section of the stone spire was damaged in an earthquake shortly after it was built and was wisely replaced in copper. The stone section was a disaster waiting to happen.
Developed architectural and structural plans have been prepared for a new earthquake resistant tower and spire of the same overall form and height. It would be built with a strong reinforced concrete square box of the same internal dimensions of the former tower and with the same three floors, first, bell ringers and belfry. It would stand on a one metre thick concrete foundation on four 1200 piles. The lower two floors of the tower would be faced with stone and have stone buttresses similar to the original tower but the upper two thirds of the tower would be fair face concrete with the form extended by steel columns grouped at the corners and at the mid-point reinforcing the vertical form of the tower. The belfry would have copper faced louvres. The spire with its four corner towers at its base and with the turreted openings to the balconies would be built with steel frames, timber rafters and purlins, and ply, copper faced, all lightweight and earthquake resistant.
The recently replaced existing roof slates could be removed by two men in a man bucket hung from a crane but the hire cost of the crane and the labour would probably exceed the value of the recovered slates.
Slates on the north face of the cathedral had lasted only 135 years. Intense sunlight had powered the surface of the slates causing them to crack and slide off the roof. The roofs would best be replaced in copper which would be permanent and more importantly lightweight considerably reducing the overall earthquake load.
The west facade
The west facade and tower of the Cathedral is the most recognisable iconic building in New Zealand. No other building is so identified with its city; it is Christchurch.
The whole of the facade, nave, side aisles and the superb narthex with all their limestone embellishments would be rebuilt to match exactly the original.
The lower part of the facade up to the underside of the rose window would be rebuilt with 150 basalt on a concrete fram and wall, and the upper part - surrounding the rose window and the high gable - with stone veneer on a steel frame to reduce the earthquake load.
The rose window would be remade with off white precast concrete with ten cinquefoils around a central decorative circle.
The beautiful narthex, architect Mountfort's superb design would be fully restored.
The structural engineer for this proposal is Grant Wilkinson. The estimated cost of this proposal, prepared by Rawlinsons Ltd, is $35.25 million, excluding increased costs and GST. This is within the insured earthquake sum for the Christ Church Cathedral.