Public Protector Thuli Madonsela accused Mr Zuma of conduct "inconsistent with his office" and said he should repay a reasonable part of the unnecessary renova-tions, which also included a chicken run and a swimming pool that had been justified as "fire-fighting equipment".
The findings were likely to further hurt the image of the scandal-plagued Mr Zuma and his ruling African National Congress (ANC) in May elections, although the former liberation movement that has ruled since the 1994 end of apartheid is still expected to win.
Ms Madonsela said in her report: "The President tacitly accepted the implementation of all measures at his residence and has unduly benefited from the enormous capital investment in the non- security installations at his residence."
The 444-page summary of the two-year investigation into the renovations at Mr Zuma's sprawling homestead at Nkandla in rural KwaZulu-Natal province painted a picture of systemic government incompetence and flouting of normal tender procedures.
Ms Madonsela described the cost overruns as "exponential" and said ministers had handled the project in an "appalling manner".
When news of the security upgrade first broke in 2009, the cost was estimated at £3.7m. However, despite intense public scrutiny, the bill ballooned to £13.8m.
The total spending amounted to eight times the estimated present-day value of securing the home of Nelson Mandela, South Africa's first black president, who died in December, aged 95.
Nic Borain, an independent political analyst, said: "This is negative for the ANC. They will lose votes as a result of this."
However, some other analysts saw it having little electoral impact because of the blanket publicity the case had already received.
Ms Madonsela's report, entitled Secure in Comfort, said public funds had to be diverted from inner-city regeneration projects to upgrade Mr Zuma's home.
It added that at no point did Mr Zuma express misgivings at its scale or opulence even though the construction would have raised the eyebrows of a reasonable person.
The report said: "A substantial amount of public money would have been saved had the president raised his concerns in time."
It detailed how a swimming pool was justified in official documents as "fire-fighting" equipment, and how Mr Zuma personally requested changes to the design of bullet-proof windows.
It also criticised the placing of a medical clinic and police facilities inside the gated compound, saying they could have been moved outside for the benefit of the public in what is one of the poorest region's of Africa's wealthiest country.
Despite concerns about fraud and shoddy public services, the ANC is almost certain to win the May 7 election, handing Mr Zuma another five years at the helm.
The government had previously gone to court to try to prevent Ms Madonsela releasing her findings on the grounds they might jeopardise Mr Zuma's security.