Every year before the monsoon, the Brihanmumbai Municipal Corporation publishes a list of buildings it considers too dangerous to live in. In 2026 that list held 174 buildings, and in many of them people were still living. Nearly all were old. For a buyer looking at a resale flat in an older Mumbai building, the audit is the building's medical history, and it is rarely offered unless you ask.
Key takeaways
- Section 353B of the Mumbai Municipal Corporation Act requires every building in use for more than 30 years to be certified fit by a structural engineer registered with the corporation, within a year of turning 30 and every 10 years after.
- The society's own bye-laws require more: under model bye-law 76, an audit every five years at 15 to 30 years of age and every three years beyond 30.
- Audited buildings are placed in categories: C1 to be vacated and demolished, C2 needing major structural repairs, C3 needing minor repairs.
- BMC's pre-monsoon list put 174 buildings in C1 as of 30 April 2026, 141 of them privately owned, with the western suburbs' wards leading the list.
- Before buying in an old building, ask for the latest audit report, its category, whether the recommended repairs were done, and how the society funded them.
The report Suresh and Kavita almost did not ask for
Suresh and Kavita (illustrative, as our stories always are), comparing places in Mumbai to stay near family for part of the year, found a well-priced resale flat in a 1988 building in the western suburbs. The flat had been freshly painted, the society was friendly, and the seller's broker described the building as "solid". Their lawyer's checklist included one item they had not heard of: the society's latest structural audit report. Names and numbers in this story are illustrative.
The society had one. It was seven years old, which is within the municipal cycle and well outside the society's own.
What a structural audit is
A structural audit is an inspection of a building's load-bearing structure by a qualified structural engineer: columns, beams, slabs, the condition of the concrete and the reinforcing steel inside it, leakages that feed corrosion, and alterations that may have weakened the frame. It ends in a report that grades the building's condition and recommends repairs.
It is not a one-time certificate. A building's structure ages, and a report that was reassuring ten years ago says little about corrosion that began five years ago. That is why the law sets intervals rather than a single check.
An analogy: a health check-up that gets more frequent with age
Most people take an annual medical check-up more seriously after 50 than at 25, and doctors recommend some tests more often as the years pass. Nobody finds that insulting. It reflects the fact that problems that were unlikely become likely, and that catching them early is far cheaper than treating them late.
The law treats buildings the same way. A building at 15 years gets checked every five years under the society's bye-laws; past 30, every three years, and the municipality requires its own certificate at 30 and every decade after. The frequency rises because the risk does.
The two clocks
A Mumbai society in an old building runs on two separate obligations, set by different laws, at different intervals.
| Municipal certificate | Society's own audit | |
|---|---|---|
| Source | Section 353B, Mumbai Municipal Corporation Act | Bye-law 76, model bye-laws for co-operative housing societies |
| Who must act | The owners and occupiers of the building | The housing society |
| When | Within a year after the building turns 30, then every 10 years, or when the corporation asks | Every 5 years at 15 to 30 years of age; every 3 years beyond 30 |
| By whom | A structural engineer registered with the corporation | An engineer on the corporation's panel, within municipal limits |
| What it produces | A certificate that the building is fit for human habitation, submitted to the corporation | An audit report for the society, with recommended repairs |
Revised model bye-laws were in draft in 2026, so confirm the bye-law number and interval in the version your society has adopted.
The building's age is not always obvious. For the municipal clock, section 353B counts 30 years from the earliest of the completion certificate, the permission to occupy, and the date at least half its built-up area was physically occupied. A building that "looks newer" may already be past 30 by the rule that counts.
What the categories mean
Audit reports in Mumbai place a building in one of a small number of categories, and the category is the line of the report that matters most to a buyer.
- C1: dangerous. The building must be vacated and demolished. It cannot be made safe by repair.
- C2: major structural repairs. C2-A needs the building, or its dangerous part, vacated for the repairs; C2-B can be repaired with residents in place. Serious, expensive, and fixable.
- C3: minor repairs. Normal maintenance of an ageing structure, due within a reasonable time.
How many buildings reach the worst category
Source: BMC pre-monsoon survey of dangerous and dilapidated buildings, figures as of 30 April 2026
Of 174 buildings BMC placed in C1 in its 2026 pre-monsoon survey, 141 were private, and the largest numbers of dilapidated private structures were in the western suburbs, in wards including H-East, H-West, K-East, K-West and P-North, with H-West and K-West holding the most C1 buildings. Many remained occupied: 79 of the 141 private buildings at the end of April, some because action was held up in court. These are the buildings at the end of a long decline. The purpose of the audit cycle is to catch the rest of the city's roughly 33,200 housing societies while their buildings are still in C3 or C2, when repair is still the answer.
The other exit from an ageing building is redevelopment, and it is running at scale. Knight Frank India counted 910 Mumbai housing societies that have signed redevelopment agreements since 2020, together set to add 44,277 new homes worth about Rs 1.3 lakh crore by 2030, with the western suburbs accounting for 73 percent of them. The same suburbs lead the C1 list. An audit report is often the first document in a society's redevelopment file, because a building's category is what tells its members whether they are choosing redevelopment or having it chosen for them.
Where buyers get it wrong
Treating the occupation certificate as permanent reassurance. An occupation certificate says the building was fit when it was completed. It says nothing about the building 30 years later.
Not asking for the report. The society holds it. A seller who says "the building is solid" is describing an opinion; the report is the evidence, and asking for it is ordinary diligence, alongside the twelve documents to check.
Reading the category and not the recommendations. A C2 or C3 report lists repairs. Ask whether they were done, when, by whom, and at what cost.
Ignoring how the repairs will be paid for. A society with a thin sinking fund pays for major repairs by special levy, and the levy falls on whoever owns the flat when it is raised. A buyer should know the repair fund and sinking fund balances before paying for a flat in a building that needs work.
Assuming redevelopment will rescue it. A building in C2 may be heading towards redevelopment, which can be good news for an owner and a long disruption for a resident. The realistic path is in self-redevelopment and what the old owner gets in a redevelopment.
Ask two questions before paying a token amount on a flat in a building over 30 years old: when was the last structural audit, and what category did it assign? A society that cannot produce a report from the last three years has not done what its own bye-laws require, and one with no certificate from the last ten years is also outside section 353B. The cost of that gap will eventually fall on its members.
What Suresh and Kavita found
The seven-year-old report had placed the building in C2, recommending repairs to corroded columns in the parking level. The society's minutes showed the repairs had been approved and only partly carried out, with the balance postponed for lack of funds. A new audit was overdue under the bye-laws, and the likely outcome was a special levy on every flat. They made an offer that priced in their share of the levy, and the seller, who knew about the report and had hoped nobody would ask, accepted most of the difference.
Where the filings come in
Old buildings sold on resale generally sit outside the MahaRERA register; the society's audit report, repair records and fund balances are the documents that matter. Where an old building is being replaced, the new project is registered, and the filing names the architect and engineer who certify its progress, the permissions on file and the construction progress. For any covered Maharashtra project, the Rs 499 ReraGenie buyer report reads that record, including the certifying architect, engineer and chartered accountant, which certificates are on file and when, and the promoter's delivery history across its other projects. Look the project up first. The certificate a structural engineer signs before a new building is permitted, and what happens when one is declared unsafe elsewhere in Maharashtra, is covered in who signed for your building.
The one-line summary
A Mumbai building over 30 must be certified by a registered structural engineer every 10 years, and its society must audit it every three: before buying in one, read the latest report, its category and whether the repairs were done, and price in the levy that will pay for the ones that were not.
Methodology and sources
- Section 353B of the Mumbai Municipal Corporation Act, 1888, which sets how a building's age is counted, and BMC's public notice on compulsory structural audit of private buildings, 11 June 2013.
- Bye-law 76 of the model bye-laws for co-operative housing societies, 2014.
- C1 figures: BMC pre-monsoon survey of dangerous and dilapidated buildings, as of 30 April 2026.
- C1 occupancy: Free Press Journal, reporting BMC's figures as of 30 April 2026.
- Redevelopment figures: Knight Frank India, Upgrading Mumbai: the redevelopment story, 2025.
- Society count: about 33,200 co-operative housing societies in Mumbai, as reported by the Free Press Journal in 2026.
This article is educational and not legal or engineering advice. For a specific building, rely on a structural engineer's report and a lawyer's reading of the society's records.
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