When establishing the conditions for managing the interventions on heritage-value properties, it is necessary avoiding transformations that lead to decay processes and make loss those characteristics defining their architecture as physical witnesses of the heritage. Therefore, the urban rules become indispensable tools when it comes to provide the guidelines for the architectonic heritage conservation. The definition of a regulatory framework for the protection of the historic downtown in Mompox started with a series of recommendations in 1970, but it is just in 1994 when they adopted the first regulations known as the Agreement No. 1. In 2010 the Special Plan for Management and Protection comes into force, which resumes some of the management conditions from the former regulations while provides some newer ones. This works presents the analysis of the provisions set out in both regulations for enlargement interventions, both in work at heights and at ground level. Both of them were based on a typological analysis of the properties and pave the road for some drastic modifications in the architecture, which would lead to the loss of the architectonic values that made the town renowned as World Heritage up to date.