Yesterday a large group defied the weather forecast and enjoyed a tour of several of the University’s heritage buildings.
For me, the recurring theme of the afternoon was the University’s special nature as a client. It’s unusual to have a client whose heritage properties span such a range of ages, styles, and typologies. The University’s buildings mostly have high levels of occupancy and usage, making it more critical that they be demonstrably safe and sound. And the University also has a kaitiakitanga role and a concern for preserving its history. For all these reasons and more, the University seems to take a more scrupulous position about how much retrofit it is prepared to do. The projects we saw were targeting 100% of the New Building Standard (NBS), which is a higher target than many clients choose to set.
It’s also a target that necessitates more physical intervention. Some of the conversation on the tour turned around questions of the practice of making these interventions visible, of leaving good records of work done, of reversibility, and of the suitability or otherwise of certain building technologies for heritage sites. Sometimes repairs can bring problems with them, if, for example, they bring moisture where it’s not wanted. We also heard a familiar story about working on heritage buildings–starting to fix one problem leads to finding several more!
I enjoyed the opportunity to hear and see some details about the specific problems heritage buildings experience, and how these are addressed. At Bayreuth (the 1903 Italianate building at 10 Grafton Road), tie rods have been inserted both parallel and perpendicular to the floor joists, binding the structure together. The brick and concrete Merchant Houses Belgrave, Okareta and Mona (12-16 Symonds St), dating from the 1880s, were suffering from water intrusion, and required structural improvement. The basement slab was relaid, with a ventilation system designed to improve airflow and remove moisture. Floors were taken up, the joists re-fixed to the walls, tongue-and-groove floorboards re-laid, plywood diaphragms used to stiffen the structure. Roof timbers were refreshed. All in all, a major refit, and one that necessitates tradeoffs between the future of the building as a whole and the integrity of its heritage fabric.
Crossing the road, we saw an elegant intervention at the General Library, where the services and stairwell were too stiff and inflexible in comparison to the abutting structure. In a decent shake, they’d likely knock the rest of the building to pieces. The solution proved to be “strengthening through de-strengthening”, in that vertical saw-cuts were used to weaken the walls, while the structural members of stairwell and library were tied together. There was an interesting conversation about the value of taking the time to allow designs to be re-thought. In this project, the initial design proposed masses of steel, strapping the disparate parts of the structure together. The final solution proved to be far more minimal, essentially a steel rod lashing elements together across the stairwell, forming a lattice. A conference panel on Alistair Cattanach of Dunning Thornton’s design for the library, with some photos, drawings, and some more information, can be found here.
Lastly, we looked at the Annexe to the Clock Tower (aka the Old Arts Building), built in the 1920s. Peter Boardman, of Structure Design, who accompanied the tour, was responsible for the highly effective post-tensioning system on the Christchurch Arts Centre, which saved it from major damage. If you’re not familiar with the Christchurch project, imagine a netting of steel cables wound around the outside of a stone building and tightened! The Clock Tower Annexe is getting a more high-tech version of this treatment, where steel rods are being inserted through the major structural members of the building. The Annexe is made from concrete faced with stone, and the steel rods, once tightened, will add some very necessary tensile strength to the building.
I’ll finish by mentioning that in response to a question from the audience about the most important lessons from the Christchurch quakes, the presenters agreed that the biggest lesson was this: doing something is better than doing nothing. Buildings which had been strengthened, even those with ad hoc solutions, survived better than those which had not. Peter suggested, as an example, that shoring up verandahs at a cost of a few thousand is often a way to reduce stresses throughout the structure, and provide protection from falling decorative elements. The two presenters also reinforced the importance of communication and compromise between members of allied professions (like architecture and engineering), and I’m sure you will all concur with this sentiment. We’re very grateful to Neil Buller and Peter Boardman for their generosity, frankness, and expertise.