Informality is a very prevalent issue especially in the urban areas of developing countries in Africa, the Middle East, Latin America
and South Asia. In the city of Nairobi, Kenya, informality is everywhere so much that it appears to be a ‘normal’ part of the urban built fabric. Muthurwa market was designed and built in 2007 for the hawkers who were operating in the CBD. However, over time since
the market came into use, informal transformations have happened and are happening to the design. These have brought about various architectural problems in the market, including: informal extensions at vendor place, dead spaces inside of market buildings as extensions head towards circulation, congestion along circulation, difficulty in way finding and lack of quality public spaces. This study examined how and why informality was happening in a formal design. Non probability sampling methods were used to select a sample from the population. Observations and interviews were used to collect the data. Quantitative and qualitative analytical procedures
were used to analyse the findings. The results of the study indicate that market was designed poorly, and without proper analysis of
the intended users. It did not consider actual effects it would bring: rather it assumed that there would be compliance. This made the users to informally transform formal spaces into informal spaces. The study recommends an inclusive design model that is as a result of understanding the ‘what is’ in the market, and recognising the limitations of the formal design.