For months, Veronique and Faustin Kla have looked for a home in Abidjan, tired of juggling their finances in the hunt for a place to raise their one-year-old son, Junior.

As in many fast-growing cities across Africa, finding affordable, decent housing is an increasingly costly headache for residents of Ivory Coast's economic capital.

"We had a budget of 80,000 CFA francs ($142), but as the search dragged on, we increased it a bit to 100,000," Faustin told AFP during a viewing, with a look of discouragement.

A report published in May by the United Nations' cities and housing agency UN Habitat said that Sub-Saharan Africa, at 55 percent, had the world's highest rate of "rental unaffordability" -- defined as households spending more than 30 percent of their income on rent.

Although Ivory Coast has enjoyed an economic boom for more than a decade, the minimum wage of 75,000 CFA francs is not enough to secure decent accommodation. 

Standing beside her husband, Veronique was running out of patience.

"Houses are too expensive," she complained, criticising also their poor condition and difficult access, with narrow sandy roads full of bumps and potholes.

Africa's urban population is expected to grow from 700 million to 1.4 billion by 2050, creating around 20 additional megacities with more than 10 million inhabitants, according to the African Union.

Abidjan's population has doubled in 20 years to exceed six million people, but the housing supply remains insufficient.

Thousands of people end up settling in precarious areas, sometimes flood-prone and officially off-limits for construction -- prompting the Ivorian government to enforce violent evictions and demolitions.

In Abidjan, estate agents charge between 5,000 and 10,000 CFA francs just to view a property, even if it is eventually judged unsuitable.

Eric Djedje said he went through that during the two months he spent searching, before finding a house in the Cocody district.

Relieved after his final viewing, he signed his rental agreement only to face another hurdle: the payments he had to make before he could move in.

With the monthly rent for the property set at 180,000 CFA francs, he was told by landlord Aboubacar Bamba that he would have to pay "a total amount of one million francs" up-front.

The sum included "two months' deposit, two months' rent in advance, one month's rent for the estate agent, water and electricity meter installation fees, as well as other additional charges", Bamba said.

Payment in instalments was not accepted, added Bamba, who owns dozens of flats in several districts of the sprawling metropolis.

Others face yet another obstacle: proving their ability to pay in a country where the informal sector employs around 90 percent of the workforce.

"The situation is unprecedented at the moment," said Yao Ernest Kouadio, a geography lecturer and researcher at Cocody University, who specialises in urban planning.

Regarding the housing supply, "government policy has not kept pace with Abidjan's population explosion," he said.

"There have never been so many informal settlements."

Urban planner Wayiribe Ouattara believes that most Ivorians migrate to Abidjan in search of work opportunities.

The city "concentrates economic activity through the port, the airport, major educational institutions and above all the government ministries", he said.

Paul Coulibaly, a student, was looking for a house for his aunt from Gagnoa in central Ivory Coast, who has recently been transferred to the economic capital.

The budget for that too had to be raised, as it was impossible to find a home for 150,000 CFA francs, he said.

Strong pressure on land prices is also driving up the cost of the tens of thousands of so-called social housing units that are supposed to be affordable, according to the urban planner.

Yet purchase prices can reach "25, 27 or even 30 million" CFA francs -- more than $53,000, Ouattara said. "How many people can afford that kind of housing?"

According to the government, Ivory Coast faces a housing deficit of 800,000 units, which grows by at least five percent every year.

It has announced plans to build 150,000 homes by 2030.