An inspection binder cannot show a trend
Owners of ageing buildings and structures commission inspection after inspection and file each one as a report. Unless every finding is tied to a fixed location and a consistent grade, decades of inspections still cannot tell the board how fast anything is deteriorating.
Japan has learnt a hard lesson about ageing structures in public. After the ceiling of a road tunnel collapsed in December 2012, road administrators across the country moved to close-range inspections of their bridges and tunnels on a five-year cycle. Owners of private structures paid attention too. Many of us inspect more often and more carefully than we did twenty years ago. My argument is that we have improved the inspecting far more than the recording, and that the recording is what a board needs.
Our property company owns some old structures. The terminal building above our Tokyo station was completed in 1971. A pedestrian deck over the station plaza in one of our suburban towns was built in 1987, and we maintain it under an agreement with the city that calls for a close inspection every five years. Beneath 4.8 kilometres of the railway's elevated track we let 212 spaces to shops, clinics, nurseries and storage tenants; the viaduct belongs to our railway company and is inspected under its own maintenance standards, but our tenants sit beneath it.
Fourteen reports and no rate of change
By 2022 the deck and the terminal building's car-park structure had been inspected fourteen times between them. Each inspection produced a report, usually from a different engineering firm, with photographs, a sketch of the structure and a table of defects graded by severity. The reports were careful, and they were filed, first on paper and later as files on a shared drive.
When our engineering department asked for a capital plan for the next fifteen years, nobody could answer the question it most needed answered: how quickly is each part of these structures getting worse? Every report described the condition on the day of inspection, and each was internally consistent. But the sketches differed from firm to firm, so the same crack appeared in different places on different drawings. Before 2004 the grading scheme had four levels with different definitions from the scheme used since. Some defects had been repaired between inspections without anyone recording that the later report was describing a repair, not a new defect.
The result was a shelf of evidence that could not support a trend. The capital plan was built, as most are, from age and rules of thumb: joints replaced every so many years, coatings renewed every so many more. I do not think that was unusual. I suspect most owners of ageing structures in Japan hold their inspection history in the same form.
A location, a grade and a date
The remedy we chose was unglamorous. Between 2023 and 2025 we fixed 1,860 locations across the deck, the car-park slabs and the terminal building's external walls, each with a permanent code and a position on a single drawing. We then went back through all fourteen reports and recorded every finding against those locations: 9,400 observations, each with the defect type, a grade on one four-step scale, the date, the inspecting firm and the photograph. Where a grade had been translated from the older scheme, the record says so, and the analysis can be run with or without those grades. Where a repair had been made, it was entered as an event of its own.
The work cost about ¥210 million, most of it engineers' time spent reading old reports, and it was not popular. Our engineering department would have preferred to spend the money on a fresh survey with laser scanning and drone photography, which would have produced a far more detailed picture of the structures today. I understood the appeal. But a new survey with no history shows a condition. What the capital plan needed was a rate, and only the old reports could supply one.
We have since rewritten our inspection contracts. Every firm now records findings against our location codes and our grading scale, and returns them as data alongside the report. New survey methods are welcome, but their results must attach to the same locations, so that each inspection adds to a series rather than starting a new one.
For the viaduct we cannot set the scheme, because the structure is the railway's. Since 2016, after a fragment of concrete fell from an unrepaired span onto a café's storeroom, the railway has sent us every finding on a tenanted span within two working days. We record them against our tenancy codes so that a shop's fit-out, a clinic's lease renewal and a span's condition can be seen together.
What the capital plan gained
Once the observations sat on one scale at fixed locations, the trends were not what anyone had assumed. The deck's expansion joints had deteriorated slowly for twenty years and then much faster after 2011, which our structural consultant attributes partly to the earthquake and partly to heavier maintenance vehicles. We brought their replacement forward from 2031 to 2027. The coating on the deck's underside, scheduled for renewal in 2026, was ageing more slowly than its specification assumed, and we deferred it by three years. On the terminal building, defects in the external wall tiles were concentrated on the north face, where the rate of new findings had doubled; the south face was stable. The capital plan now treats the faces separately.
The money roughly balanced, but that is not the point. The board can now see why each major repair falls in the year it does, and the next inspection will either confirm the rate or change it. That evidence matters most for the decision now ahead of us: whether to refurbish the 1971 terminal building or rebuild it. Neither answer can be defended to tenants, to the railway or to the group's shareholders on the basis of a building's age alone.
For directors of any company that owns ageing structures, the useful question is simple. Ask management not what the last inspection found, but how fast the worst defects are progressing and how they know. If the answer comes from a binder, the company is commissioning inspections without yet learning from them. The remedy is cheaper than a new survey and slower than anyone would like, but it is the only way to turn decades of careful observation into a rate the board can plan against.