Wise words to heed when considering the upgrade of a heritage building are “do as little as possible but as much as is necessary”.

They were echoed very neatly when Cardinal John Dew briefed Jane Kelly, the architect commissioned for the upgrading of the Cathedral of the Sacred Heart in Wellington. He said to her: “Strengthen the building, keep it simple, focus on the altar.”

A succinct brief, and the resulting upgrade of the Cathedral, completed in June 2024, can be fairly assessed as meeting it.

The Metropolitan Cathedral of the Sacred Heart stands in Hill Street, Thorndon, prominent for its magnificent Classical portico, lording it over the Gothic of the Parliamentary Library further down Hill Street. It is the work of architect F W Petre, sometimes known as ‘Concrete Petre’ for his innovative use of the material, but more especially known for a remarkable series of Basilican-style Catholic churches. These include those in Ōamaru, Tīmaru, Waimate and, most especially, Christchurch; the latter, one of our greatest architectural treasures, was seriously damaged in the earthquakes of 2011 and later demolished.

I recently had two hours in the building with Jane Kelly, project architect of Team Architects, and Paul Cummack, conservation architect. The project was initiated because a structural analysis in 2018 showed that the building was earthquake prone, at 15 per cent NBS. This led to immediate closure and the simple spoken brief to the architect quoted earlier.

Strengthening was clearly the motivating force, and the building now stands at 50 per cent NBS. The work involved a steel diaphragm above and in the plane of the ceiling; bracing in the roof planes; post-tensioned longitudinal steel ties, and vertical steel in the columns. Extensive though this sounds, the wonderful coffered ceiling of the nave was left undisturbed, and, although the roof cladding had to be removed, this was pressed metal tiles of modern origin and without heritage significance. Nothing of the structural work is visible unless one delves into service or roof spaces.

During the course of this work, it became clear that the fabric of the building was suffering from serious decay. Cummack took moisture readings of the Ōamaru stonework over large areas of the internal wall surfaces, finding some of it at 99 per cent; the saturated masonry had, in turn, rusted the steel ties that held the inner skin of Ōamaru stone to the brickwork of the exterior, and some wall planes were distorting as a result.

It is said that one coat of paint 50 microns thick can make the difference between good and bad conservation, and nowhere was this more true than here with 400 microns of paint; it was paint coatings that actually threatened the stability of the building. The interior stone had been painted many times, forming an impervious skin that held the errant moisture that made its way through the brickwork, the random rubble infill and the stone. This paint was laboriously taken off with an ingenious array of purpose-made hand planes, by four workers over eight months, while, on the outside, weathering improvements were made to window sills and flashings. Fretted and spalled stone and brick surfaces were repaired with carefully let-in new material: visible but discreet. Not only did the moisture readings drop dramatically within weeks of the removal of the paint, but the warm glow of the Ōamaru stonework is, now, once again a defining feature of the interior. One can only guess that the painting of the interior was a vain attempt to cure the dampness problem.

The Cardinal’s words “focus on the altar” could hardly have been more faithfully met. St Gerard’s Monastery Chapel standing above Oriental Bay was designed by John Swan in 1908. When it was sold by ICPE Mission, a Catholic organisation, to a secular owner, they gifted the altar to the Cathedral as part of the sale agreement: a beautiful Italian-made marble and mosaic piece that is now the focal point of the chancel. It replaces a modern altar and has been placed forward of the original position to meet present-day liturgical needs. Modern chipboard flooring and carpet in the chancel were removed to reveal long-hidden mosaic tilework on the floor. The risers of the steps and the bases of the columns were all in remarkably good condition but calling for careful repair in small local areas; it is now hard to detect those repairs.

As well as the Cardinal’s brief, the work was guided by a conservation plan for the Cathedral prepared in 1998 by Salmond Reed Architects. Although it was out of date in respect of district plan and building consent matters, it held good in history and assessment of significance matters, and it served as a base document for the work. Kelly was frequently in touch with staff at Salmond Reed, and she had discussions at critical times with City Council and Heritage New Zealand staff.

As for consenting matters, a building consent was issued for the structural work; all else was judged to be repair and maintenance with no consent required. Although listed on the District Plan as a heritage building, exterior only, a resource consent was unnecessary since the only external change was making good to defective fabric. That is until it was decided to alter the porch, which is part of a 1980s’ addition to the original building, designed by Melling Morse Architects. Since it is an integral part of the building, it is also a part of the heritage listing.

The project was drawn out — 2018 to 2024 — Covid being responsible for a good portion of this time, and discoveries along the way extended the scope of the work. In retrospect, both Kelly and Cummack said that, ideally, more investigative work should have been done at the beginning, and the work would have been planned differently. Good practice would have required that the conservation plan be updated, too.

The project cost came to approximately $13m, a generous $8m of which came from the Government’s ‘Shovel Ready’ initiative in the wake of Covid.

A vitally important category 1 heritage building now stands structurally secure, with fabric defects eliminated and weathering capacity greatly improved. The grand portico of the front elevation is looking formidable and the exterior generally well cared for. I join with some parishioners in finding the distressed pattern of the carpet (“reminiscent of flagstones”) inappropriate in such a formal and ordered building but, that aside, one can applaud the return of the beauty and authenticity of the Ōamaru stonework, of the newly revealed mosaics, and of the re-ordered chancel with a beautiful altar. This upgrade, significant in the life of the building, has been achieved with a commendable respect for and minimal disturbance of heritage fabric… “as little as possible but as much as was necessary”.