Can backyard extensions cure global housing shortage?

Backyard extensions have been identified in a United Nations-sanctioned report as one of the solutions countries can adopt to cure the housing crisis.

The World Cities Report 2026, unveiled during the 13th World Urban Forum held in Baku, Azerbaijan, notes that some of the solutions being deployed by governments to address housing shortage are slow and unresponsive in some segments of the market.

As such, some sections of the housing market have been devising their own community-bred solutions which offer a faster and cost-effective way to address the shortage.

One of them is infill housing, where backyard extension falls.

The persistent and complex nature of the housing crisis, combined with slow responses, small in scale and often still unaffordable, has led to growing interest in more flexible, temporary approaches to housing delivery, occupation and management,” the report says.

The report presents infill housing, flexible housing and temporary housing as the three adaptive solutions.

The report by UN-Habitat says infill housing is used as an umbrella term that encompasses secondary and accessory dwelling units.

These units include tiny homes, resident-initiated extensions, the restoration of previously habitable units, the subdivision of larger homes, and the conversion of non-residential spaces such as offices into housing units.

“These forms of development generally help fill gaps in the housing market, particularly for smaller units and for specific population groups,” the report says.

It explains that infill housing often operates in grey areas of existing regulatory frameworks.

“For instance, secondary units built in backyards are typically smaller and lighter structures, meaning they may face less stringent building codes, fewer requirements for environmental impact assessments, and no need to upgrade local infrastructure,” the report says.

The report says in some jurisdictions, regulations have been amended to encourage infill, such as by easing land-use restrictions.

It gives the city of Los Angeles (United States) as an example, noting that it has adopted policies on accessory dwelling units that have broadened where and how these units can be constructed.

The mushrooming of backyard extensions is quite common in Nairobi, particularly within government housing and private stand-alone dwellings, which are usually gated. Some of these structures are permanent, while others are temporary.

Iron sheet and wood are the most used materials by the landlords of these structures, as they know they are likely to be demolished since they have not been authorised by the county government.

Modern developers, however, are building main units with extensions that come as either a rental property, a guest house or where workers can stay.

The World Cities Report 2026 debunks that such units are not only a preserve of the developing world, where Kenya falls.

“Informal housing practices are present and increasingly prevalent worldwide, driven significantly by the current housing crisis. In the US, informally built Accessory Dwelling Units have been widely adopted: in Los Angeles, California, it is estimated that about 10 per cent of single-family housing units have an informal second unit,” the report says.

In Europe, it says, the informal adaptation of formal or state-built housing complexes is a widespread practice.

“In London, United Kingdom, incremental backyard extensions are common in both high- and low-income areas,” the report adds.

The report says informally built housing and neighbourhoods are constantly undergoing self-initiated maintenance, repairs and upgrading, even though formal land and housing policies are often poorly aligned with their needs and realities.

“Informal housing is also widespread in high-income countries, where backyard units, basement apartments, rooftop dwellings, accessory dwelling units and unauthorised subdivisions have become an increasingly important source of low-cost housing,” the report says.

In Kenya, the government has been trying to regularise these informal backyard extensions through the enactment of laws and subsequent regulations.

This is through the Nairobi City County Regularisation of Unauthorised Developments Act, 2025 and the Physical and Land Use Planning Act, 2022. 

Nairobi City County, evidently, is the most affected urban area in the country, considering the migration of job seekers invading the city for job opportunities, which deepens the housing crisis. Countrywide, the housing unit shortage stands at two million. 

The Physical and Land Use Planning Act, 2022 states that any person who intends to erect a new building or make alterations or additions to an existing building, whether permanent or temporary, shall be required to submit building plans before obtaining development permission.

The Act does exempt some structures from this provision, among them a dog kennel, a poultry house, a greenhouse not more than 500 square metres in an urban setting, a car shade, a gazebo, a site house and a temporary tent that will be in use for not more than 30 days.

The Nairobi City County Regularisation of Unauthorised Developments Act, 2025, provides instances where the county will not regularise an already put-up development.

These include unauthorised development done on land belonging to the county government and not allotted, or developments done on land earmarked for public utility.

Developments on water bodies like tank beds, river beds, natural drainage and such are also not to be regularised.

 The Act provides that once the owner submits to regularise their development, any case filed against them by the County will be withdrawn.

 “On regularisation of unauthorised development under this Act, all court cases or other proceedings, filed by the Executive Committee Member, the occupant, and owner or otherwise and pending in any court in so far as they relate to the state of being unauthorised, shall stand abated,” the Act states.