After decades of renting being the norm, companies with offices in the world’s major cities are seeing more financial sense in buying their own buildings, prompted by a mix of cheap debt, stockpiled cash and new accounting rules.

Having culled staff in the wake of the financial crisis, businesses are now scrutinising real estate costs and capitalising on an opportunity not present for at least half a century to cut what is often their second-highest outgoing.

As central banks keep interest rates historically low to kickstart economic growth, the resulting cheap cost of borrowing ends “fifty years of perceived wisdom” that companies shouldn’t tie up cash in property, said Chris Simmons, founder of Real Estate Forecasting.

There was a fivefold increase in the value of occupier deals in London last year versus 2011, a tenfold increase in New York and a sevenfold increase in Hong Kong, data produced for Reuters by research company Real Capital Analytics shows.

Among companies that have recently bought their own real estate are WPP Group and Google in New York and Manulife and Hang Seng Bank in Hong Kong, according to RCA data.

“We are at a moment in time when all the planets are aligned for companies to buy property,” said Chris Lewis, a real estate advisor at accountant Deloitte. “The idea is starting to gain traction and you’ll see a sustained increase over the next several years.”

Cigarette producer British American Tobacco, which bought its headquarters on the north bank of London’s River Thames for 190 million pounds ($298 million) last year, described the deal as “financially attractive”.

The rental yield of about 5.5 percent, or the annual rent as a percentage of the property’s value, was more than double its current ten-year corporate bond yield of 2.4 percent, according to Thomson Reuters data.

In other words, if it funded the purchase by issuing ten-year bonds, the annnual interest bill would be less than half the annual rent bill, a saving that would come on top of any future rise in the property’s value.

Such office deals are “at unprecedented levels” due to cheap loans as well as the cash many have hoarded in choppy economic times, said Robert Matthews, head of international real estate at Scottish Widows Investment Partnership (SWIP), which has 8.2 billion pounds of property under management.

“We recently sold two properties in greater Paris for exactly these reasons,” he said.

Proposed changes under International Financial Reporting Standards expected in 2016 or 2017 could strengthen the case for ownership. Under the new rules, all outstanding payments over a lease’s term must appear on the balance sheet. Currently, only the annual rent goes through the profit and loss account.

The appearance of larger liabilities may affect how a company is viewed by lenders and ratings agencies and hurt its ability to borrow, said Michael Evans at real estate consultant Jones Lang LaSalle.

“The changes give property costs a higher profile in the minds of CEOs and FDs,” he said.

Buying is not always an option and wouldn’t work for a building with several tenants, for example. Other companies would be reluctant to tie up cash in such long-term deals, particularly those with smaller cash holdings or that need it for more pressing issues like overseas growth or acquisitions.

If problems arose, companies would also be hit by the double impact of a business doing badly and a property that drops in value because it houses a financially shaky tenant.

Overall property costs are typically between eight and ten percent of total costs but can be shrunk by squeezing more staff into re-configured space.

Efficient designs which can save companies millions, are a major selling point of new buildings like Land Securities’ Walkie Talkie skyscraper in London.

“Real estate decisions have become a board level issue and are no longer the preserve of the property manager,” Lewis said. “Most FTSE 350 companies are taking a long hard look at their property costs.”