Interventions on the continent that seek to stimulate affordable housing supply typically focus on the formal, developer-built segment of the market with an emphasis on ownership, often facilitated by mortgage finance. In contrast with this focus, actual housing supply is dominated by what we might call informal and/or incremental development predominantly for rental.

A particularly responsive form of supply is by existing property owners who may or may not have formal title for their properties. They develop rental units in their backyards or redevelop the entire property for rental. The quality of this housing varies, but is largely characterised as sub-standard, contributing to what is known as the qualitative backlog.

Rental units are commonly developed near employment opportunities where demand for affordable housing is high. The neighbourhoods in which they are located are often unpaved and with poor or no stormwater drainage, and in most cases the units lack reliable access to critical services such as piped water on the stand and waterborne sewage. An additional characteristic they share is the lack of adherence to official building codes.

This lack of compliance / governance is not necessarily always a problem for someone to solve. When single storey structures are in a backyard and are made from less durable materials they can be redeveloped in time when there is sufficient financial incentive. These structures can be easily demolished in the next generation to make way for 100-year durable, taller and hopefully compliant structures to be inhabited by a new recognisably ‘middle class’ middle class that is likely to exist by then.

On the other hand, lack of governance and compliance spells total disaster in the context of newly constructed high rise, durable housing. Based on available data, these appear to be the exception – currently. But the exception is noteworthy because it should sound a warning to cities across the continent, particularly those that are budget- and capacity-constrained, and experiencing rapid urbanisation. For example, in Pipeline in Nairobi, landowners have built multi-storey units that are often not serviced and not built to code to meet the demand for well-located, affordable housing (rental in the region of USD40-100 per month depending on the unit). The building footprint typically is edge to edge, with many units lacking natural light and ventilation as only street-facing units have windows. Obviously, there are no elevators.

Photographs: Pipeline, Nairobi (own pictures)

In contrast with vertical slums that go wrong as originally compliant, serviced high-rise buildings degenerate over time, newly built vertical slums start wrong. They are not built to code and are located in areas that lack infrastructure making upgrading difficult. The context is also much trickier to upgrade than the standard low-rise slum as many solutions are simply infeasible. Land readjustment that frees up land for development by densification is obviously impossible as the densities are already maximised (or are arguably over-extended). Retrofitting infrastructure is that much more costly as the built environment cannot be easily dismantled. Relocating households is that much more difficult because there are so many more of them. Demolition, even when it is called for, is rare because the property owner is unlikely to stand idly by. There is simply too much capital tied up in a multi-storey building.

And then of course, because the dominant tenure is rental, there are concerns about rents in the economic sense of the word. If the city were to upgrade the roads for instance, landlords might simply capture all the value. They would probably put up the rent and displace sitting tenants in the process. They would also probably continue to avoid paying taxes, so there is no business case to be made for the investment.

The appealing alternative is to do nothing. Bad buildings will eventually collapse on their own and with a bit of luck there will be few injuries or fatalities. Those buildings that stand the test of time will probably continue to provide sub-standard but very affordable housing. And hopefully the households who live there will move up and out in time.

Clearly, the lesson for cities is not to allow a Pipeline to develop in the first place. Investing in infrastructure is critical but so too is governance and compliance. Preventing Pipeline will require ‘whack a mole’ vigilance which might stand a chance of success if it is enabled by good tech. But beyond stopping illegal activity, cities will have to develop the capacity to manage and support high-rise incrementalism. They will also have to develop the capacity to engage productively with property owners who may not welcome the imposition of additional taxes or restrictions on what and how they build.

It is not clear what this capacity looks like and how it can be created. As a first step it may be useful for global development institutions that have experience in this sphere to share their knowledge. Beyond this, it may also be useful to establish local pilot support centres in specific locations. Where risks of failure are high, it may be ideal for these not to be run by local government but rather by independent organisations that work in loose collaboration with local government, with on-going feedback and interaction between the support centre and city officials at executive and operational level. These support centres would seek to understand and influence landlords by providing access to affordable (or fully subsidised) professional services including design, drafting, engineering and construction management. They could also provide information on finance, green building materials and technologies, sanitation and water solutions. Services might also include tenant and property management solutions where these are not available.

By documenting case studies carefully, the pilot projects would develop an in-depth, client-based understanding of city planning submission and approval processes. They would also generate good data on costs of construction. Case studies could also shed light on landlord incentives to comply with planning processes and to pay for services and taxes. They might also shed light on landlord investment decision-making processes. Through this, these pilot centres would be able to identify specific, implementable interventions including opportunities to streamline processes and realign building codes to support the development of better quality, affordable, high rise residential accommodation in rapidly growing cities.